Lysosome: Difference between revisions
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{{short description|Cell membrane organelle}} |
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[[Image:Illu cell structure.jpg|thumb|350px|Various [[organelles]] labeled. The '''lysosome''' is labeled in the upper left.]] |
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{{Distinguish|Lysozyme|lectins}} |
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{{Use dmy dates|date=August 2017}} |
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{{Organelle diagram}} |
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A '''lysosome''' ({{IPAc-en|ˈ|l|aɪ|s|ə|ˌ|s|oʊ|m}}) is a single [[membrane-bound organelle]] found in many<!--red blood cells and some other specialized cells don't have lysosomes--> animal [[Cell (biology)|cell]]s.<ref>{{cite journal |vauthors=Wu Y, Huang P, Dong XP |title=Lysosomal Calcium Channels in Autophagy and Cancer |journal=Cancers |volume=13 |issue=6 |date=March 2021 |page=1299 |pmid=33803964 |pmc=8001254 |doi=10.3390/cancers13061299 |doi-access=free |url=}}</ref><ref>By convention similar cells in plants are called [[vacuoles]], see {{Section link||Controversy in botany}}</ref> They are spherical [[Vesicle (biology and chemistry)|vesicles]] that contain [[Hydrolysis|hydrolytic]] [[enzyme]]s that digest many kinds of [[biomolecule]]s. A lysosome has a specific composition, of both its [[membrane protein]]s and its [[lumen (anatomy)|lumenal]] proteins. The lumen's pH (~4.5–5.0)<ref>{{cite journal | vauthors = Ohkuma S, Poole B | title = Fluorescence probe measurement of the intralysosomal pH in living cells and the perturbation of pH by various agents | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 75 | issue = 7 | pages = 3327–3331 | date = July 1978 | pmid = 28524 | pmc = 392768 | doi = 10.1073/pnas.75.7.3327 | doi-access = free | bibcode = 1978PNAS...75.3327O }}</ref> is optimal for the enzymes involved in hydrolysis, analogous to the activity of the [[stomach]]. Besides degradation of polymers, the lysosome is involved in cell processes of secretion, [[plasma membrane]] repair, [[apoptosis]], [[cell signaling]], and [[energy metabolism]].<ref>{{cite journal | vauthors = Settembre C, Fraldi A, Medina DL, Ballabio A | title = Signals from the lysosome: a control centre for cellular clearance and energy metabolism | journal = Nature Reviews. Molecular Cell Biology | volume = 14 | issue = 5 | pages = 283–296 | date = May 2013 | pmid = 23609508 | pmc = 4387238 | doi = 10.1038/nrm3565 }}</ref> |
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[[File:Lysosomes Digestion.svg|thumb|Lysosomes digest material. Step one shows material entering a food vacuole through the plasma membrane, a process known as endocytosis. In step two a lysosome with an active hydrolytic enzyme comes into the pictures as the food vacuole moves away from the plasma membrane. Step three consists of the lysosome fusing with the food vacuole and hydrolytic enzymes entering the food vacuole. In the final step, step four, hydrolytic enzymes digest the food particles.<ref>{{cite book | vauthors = Holtzclaw FW, etal | title = AP* Biology: to Accompany Biology | edition = 8th AP | publisher = Pearson Benjamin Cummings | date = 2008 }}</ref>]] |
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[[image:biological_cell.svg|thumb|350px|Schematic of typical animal cell, showing subcellular components. [[Organelle]]s:<br/> |
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(1) [[nucleolus]]<br/> |
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(2) [[cell nucleus|nucleus]]<br/> |
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(3) [[ribosomes]] (little dots)<br/> |
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(4) [[vesicle (biology)|vesicle]]<br/> |
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(5) rough [[endoplasmic reticulum]] (ER)<br/> |
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(6) [[Golgi apparatus]]<br/> |
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(7) [[Cytoskeleton]]<br/> |
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(8) smooth [[endoplasmic reticulum]]<br/> |
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(9) [[mitochondrion|mitochondria]]<br/> |
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(10) [[vacuole]]<br/> |
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(11) [[cytoplasm]]<br/> |
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(12) [[lysosome]]<br/> |
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(13) [[centriole]]s within [[centrosome]]]] |
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Lysosomes are degradative organelles that act as the waste disposal system of the cell by digesting used materials in the [[cytoplasm]], from both inside and outside the cell. Material from outside the cell is taken up through [[endocytosis]], while material from the inside of the cell is digested through [[autophagy]].<ref name = "Underwood_2018" /> The sizes of the organelles vary greatly—the larger ones can be more than 10 times the size of the smaller ones.<ref>{{cite book| veditors = Zaftig P | title = Lysosomes | chapter = History and Morphology of Lysosome | vauthors = Lüllmznn-Rauch R | date = 2005 | publisher = Landes Bioscience/Eurekah.com | location=Georgetown, Tex. | isbn = 978-0-387-28957-1 | edition = Online-Ausg. 1 | pages = 1–16 | chapter-url = https://books.google.com/books?id=mTgNUPS5tcUC}}</ref> They were discovered and named by Belgian biologist [[Christian de Duve]], who eventually received the [[Nobel Prize in Physiology or Medicine]] in 1974. |
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'''poop''' are [[organelle]]s that contain [[digestive enzyme]]s (acid [[hydrolase]]s). They digest excess or worn-out [[organelle]]s, food particles, and engulfed [[virus]]es or [[bacteria]]. The [[biological membrane|membrane]] surrounding a lysosome allows the [[digestive enzyme]]s to work at the 4.5 [[pH]] they require. Lysosomes fuse with [[vacuole]]s and dispense their enzymes into the [[vacuole]]s, digesting their contents. They are created by the addition of hydrolytic enzymes to early endosomes from the [[Golgi apparatus]]. The name ''lysosome'' derives from the Greek words ''lysis'', which means dissolution or destruction, and ''soma'', which means body. They are frequently nicknamed "suicide-bags" or "suicide-sacs" by cell biologists due to their role in [[autolysis]]. Lysosomes were discovered by the Belgian cytologist [[Christian de Duve]] in 1949. |
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Lysosomes contain more than 60 different enzymes, and have more than 50 membrane proteins.<ref>{{cite journal | vauthors = Xu H, Ren D | title = Lysosomal physiology | journal = Annual Review of Physiology | volume = 77 | issue = 1 | pages = 57–80 | date = 2015 | pmid = 25668017 | pmc = 4524569 | doi = 10.1146/annurev-physiol-021014-071649 }}</ref><ref>{{cite web|title=Lysosomal Enzymes|url=https://www.rndsystems.com/research-area/lysosomal-enzymes|website=www.rndsystems.com|publisher=R&D Systems|access-date=4 October 2016}}</ref> Enzymes of the lysosomes are synthesized in the [[rough endoplasmic reticulum]] and exported to the [[Golgi apparatus]] upon recruitment by a complex composed of [[CLN6]] and [[CLN8]] proteins.<ref name="di Ronza, A. 2018">{{cite journal | vauthors = di Ronza A, Bajaj L, Sharma J, Sanagasetti D, Lotfi P, Adamski CJ, Collette J, Palmieri M, Amawi A, Popp L, Chang KT, Meschini MC, Leung HE, Segatori L, Simonati A, Sifers RN, Santorelli FM, Sardiello M | display-authors = 6 | title = CLN8 is an endoplasmic reticulum cargo receptor that regulates lysosome biogenesis | journal = Nature Cell Biology | volume = 20 | issue = 12 | pages = 1370–1377 | date = December 2018 | pmid = 30397314 | pmc = 6277210 | doi = 10.1038/s41556-018-0228-7 }}</ref><ref name="pmid32597833">{{cite journal | vauthors = Bajaj L, Sharma J, di Ronza A, Zhang P, Eblimit A, Pal R, Roman D, Collette JR, Booth C, Chang KT, Sifers RN, Jung SY, Weimer JM, Chen R, Schekman RW, Sardiello M | display-authors = 6 | title = A CLN6-CLN8 complex recruits lysosomal enzymes at the ER for Golgi transfer | journal = The Journal of Clinical Investigation | volume = 130 | issue = 8 | pages = 4118–4132 | date = August 2020 | pmid = 32597833 | pmc = 7410054 | doi = 10.1172/JCI130955 | doi-access = free }}</ref> The enzymes are transported from the [[Golgi apparatus]] to lysosomes in small vesicles, which fuse with larger acidic vesicles. Enzymes destined for a lysosome are tagged with the molecule [[mannose 6-phosphate]], so that they are properly sorted into acidified vesicles.<ref>{{cite journal | vauthors = Saftig P, Klumperman J | title = Lysosome biogenesis and lysosomal membrane proteins: trafficking meets function | journal = Nature Reviews. Molecular Cell Biology | volume = 10 | issue = 9 | pages = 623–635 | date = September 2009 | pmid = 19672277 | doi = 10.1038/nrm2745 | s2cid = 24493663 }}</ref><ref>{{cite journal | vauthors = Samie MA, Xu H | title = Lysosomal exocytosis and lipid storage disorders | journal = Journal of Lipid Research | volume = 55 | issue = 6 | pages = 995–1009 | date = June 2014 | pmid = 24668941 | pmc = 4031951 | doi = 10.1194/jlr.R046896 |doi-access=free }}</ref> |
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At [[pH]] 4.8, the interior of the lysosomes is more acidic than the [[cytosol]] (pH 7.2). The lysosome's single [[Cell membrane|membrane]] stabilizes the low pH by pumping in [[proton]]s (H<sup>+</sup>) from the cytosol via [[proton pump]]s and chloride [[ion channel]]s. The membrane also protects the cytosol, and therefore the rest of the [[cell (biology)|cell]], from the [[degradative enzyme]]s within the lysosome. For this reason, should a lysosome's acid [[hydrolases]] leak into the cytosol, their potential to damage the cell will be reduced, because they will not be at their optimum pH. |
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In 2009, Marco Sardiello and co-workers discovered that the synthesis of most lysosomal enzymes and membrane proteins is controlled by transcription factor EB ([[TFEB]]), which promotes the transcription of [[nuclear gene]]s.<ref name = "Underwood_2018">{{cite journal|title=When the brain's waste disposal system fails |journal=Knowable Magazine | vauthors = Underwood E |doi=10.1146/knowable-121118-1 |url=https://www.knowablemagazine.org/article/living-world/2018/when-brains-waste-disposal-system-fails|year=2018 |s2cid=187669426 |doi-access=free }}</ref><ref name="pmid19556463">{{cite journal | vauthors = Sardiello M, Palmieri M, di Ronza A, Medina DL, Valenza M, Gennarino VA, Di Malta C, Donaudy F, Embrione V, Polishchuk RS, Banfi S, Parenti G, Cattaneo E, Ballabio A | display-authors = 6 | title = A gene network regulating lysosomal biogenesis and function | journal = Science | volume = 325 | issue = 5939 | pages = 473–477 | date = July 2009 | pmid = 19556463 | doi = 10.1126/science.1174447 | s2cid = 20353685 | bibcode = 2009Sci...325..473S | doi-access = free }}</ref> [[Mutation]]s in the genes for these enzymes are responsible for more than 50 different human [[genetic disorder]]s collectively known as [[lysosomal storage disease]]s. These diseases result in an accumulation of specific [[Substrate (chemistry)|substrates]], due to the inability to break them down. These genetic defects are related to several [[neurodegenerative disorders]], cancers, [[cardiovascular diseases]], and [[ageing|aging-related]] diseases.<ref name="platt">{{cite journal | vauthors = Platt FM, Boland B, van der Spoel AC | title = The cell biology of disease: lysosomal storage disorders: the cellular impact of lysosomal dysfunction | journal = The Journal of Cell Biology | volume = 199 | issue = 5 | pages = 723–734 | date = November 2012 | pmid = 23185029 | pmc = 3514785 | doi = 10.1083/jcb.201208152 }}</ref><ref>{{cite journal | vauthors = He LQ, Lu JH, Yue ZY | title = Autophagy in ageing and ageing-associated diseases | journal = Acta Pharmacologica Sinica | volume = 34 | issue = 5 | pages = 605–611 | date = May 2013 | pmid = 23416930 | pmc = 3647216 | doi = 10.1038/aps.2012.188 }}</ref><ref name="The crucial impact of lysosomes in">{{cite journal | vauthors = Carmona-Gutierrez D, Hughes AL, Madeo F, Ruckenstuhl C | title = The crucial impact of lysosomes in aging and longevity | journal = Ageing Research Reviews | volume = 32 | pages = 2–12 | date = December 2016 | pmid = 27125853 | pmc = 5081277 | doi = 10.1016/j.arr.2016.04.009 }}</ref> |
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==Enzymes== |
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Some important enzymes in these are: |
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==Etymology and pronunciation== |
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*[[Lipase]], which digests [[lipid]]s |
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The word ''lysosome'' ({{IPAc-en|ˈ|l|aɪ|s|oʊ|s|oʊ|m}}, {{IPAc-en|ˈ|l|aɪ|z|ə|z|oʊ|m}}) is [[Neo-Latin]] that uses the [[classical compound|combining forms]] ''lyso-'' (referring to [[wikt:lysis#Noun|lysis]] and derived from the Latin ''[[wikt:lysis#Latin|lysis]]'', meaning "to loosen", via Ancient Greek λύσις [lúsis]), and ''[[wikt:-some#Etymology 3|-some]]'', from ''[[soma (biology)|soma]]'', "body", yielding "body that lyses" or "lytic body". The adjectival form is ''lysosomal''. The forms ''*lyosome'' and ''*lyosomal'' are much rarer; they use the ''[[wikt:lyo-#Prefix|lyo-]]'' form of the prefix but are often treated by readers and editors as mere unthinking replications of [[typographical error|typos]], which has no doubt been true as often as not. |
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*[[Carbohydrase]]s, which digest [[carbohydrate]]s (e.g., sugars) |
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*[[Protease]]s, which digest [[protein]]s |
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*[[Nuclease]]s, which digest [[nucleic acid]]s |
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*[[phosphoric acid]] monoesters. |
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==Discovery== |
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Lysosomal enzymes are synthesized in the cytosol and the [[endoplasmic reticulum]], where they receive a [[mannose|mannose-6-phosphate]] tag that targets them for the lysosome. Aberrant lysosomal targeting causes [[inclusion-cell disease]], whereby enzymes do not properly reach the lysosome, resulting in accumulation of waste within these organelles. |
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[[File:The Biological bulletin (19756543133).jpg|thumb|TEM views of various vesicular compartments. Lysosomes are denoted by "Ly". They are dyed dark due to their acidity; in the center of the top image, a Golgi Apparatus can be seen, distal from the cell membrane relative to the lysosome .]] |
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[[Christian de Duve]], at the Laboratory of Physiological Chemistry at the [[Université Catholique de Louvain|Catholic University of Louvain]] in Belgium, had been studying the mechanism of action of [[insulin]] in liver cells. By 1949, he and his team had focused on the enzyme called [[glucose 6-phosphatase]], which is the first crucial enzyme in sugar metabolism and the target of insulin. They already suspected that this enzyme played a key role in regulating [[blood sugar levels]]. However, even after a series of experiments, they failed to purify and isolate the enzyme from the cellular extracts. Therefore, they tried a more arduous procedure of [[cell fractionation]], by which cellular components are separated based on their sizes using [[centrifugation]]. |
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They succeeded in detecting the enzyme activity from the [[microsome|microsomal]] fraction. This was the crucial step in the serendipitous discovery of lysosomes. To estimate this enzyme activity, they used that of the standardized enzyme [[acid phosphatase]] and found that the activity was only 10% of the expected value. One day, the enzyme activity of purified cell fractions which had been refrigerated for five days was measured. Surprisingly, the enzyme activity was increased to normal of that of the fresh sample. The result was the same no matter how many times they repeated the estimation, and led to the conclusion that a membrane-like barrier limited the accessibility of the enzyme to its substrate, and that the enzymes were able to diffuse after a few days (and react with their substrate). They described this membrane-like barrier as a "saclike structure surrounded by a membrane and containing acid phosphatase."<ref>{{cite journal |author= Susana Castro-Obregon|year= 2010 |title= The Discovery of Lysosomes and Autophagy |url= http://www.nature.com/scitable/topicpage/the-discovery-of-lysosomes-and-autophagy-14199828|journal= Nature Education |volume=3 |issue= 9 | pages=49 }}</ref> |
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==Functions== |
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The lysosomes are used for the digestion of [[macromolecule]]s from [[phagocytosis]] (ingestion of other dying cells or larger extracellular material), [[endocytosis]] (where [[Receptor (biochemistry)|receptor protein]]s are recycled from the cell surface), and [[autophagy]] (wherein old or unneeded organelles or proteins, or microbes that have invaded the cytoplasm are delivered to the lysosome). Autophagy may also lead to [[autophagy|autophagic cell death]], a form of [[programmed cell death|programmed self-destruction]], or [[autolysis]], of the cell, which means that the cell is digesting itself. |
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It became clear that this enzyme from the cell fraction came from membranous fractions, which were definitely cell organelles, and in 1955 De Duve named them "lysosomes" to reflect their digestive properties.<ref>{{cite journal | vauthors = de Duve C | title = The lysosome turns fifty | journal = Nature Cell Biology | volume = 7 | issue = 9 | pages = 847–849 | date = September 2005 | pmid = 16136179 | doi = 10.1038/ncb0905-847 | s2cid = 30307451 }}</ref> The same year, [[Alex B. Novikoff]] from the [[University of Vermont]] visited de Duve's laboratory, and successfully obtained the first [[electron microscope|electron micrographs]] of the new organelle. Using a staining method for acid phosphatase, de Duve and Novikoff confirmed the location of the [[hydrolase|hydrolytic enzymes]] of lysosomes using [[light microscope|light]] and electron microscopic studies.<ref>{{cite journal | vauthors = Novikoff AB, Beaufay H, De Duve C | title = Electron microscopy of lysosomerich fractions from rat liver | journal = The Journal of Biophysical and Biochemical Cytology | volume = 2 | issue = 4 Suppl | pages = 179–184 | date = July 1956 | pmid = 13357540 | pmc = 2229688 | doi = 10.1083/jcb.2.4.179 }}</ref><ref>{{cite journal | vauthors = Klionsky DJ | title = Autophagy revisited: a conversation with Christian de Duve | journal = Autophagy | volume = 4 | issue = 6 | pages = 740–743 | date = August 2008 | pmid = 18567941 | doi = 10.4161/auto.6398 | doi-access = }}</ref> de Duve won the [[Nobel Prize in Physiology or Medicine]] in 1974 for this discovery. |
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Other functions include digesting foreign bacteria (or other forms of waste) that invade a cell and helping repair damage to the [[plasma membrane]] by serving as a membrane patch, sealing the wound. In the past, lysosomes were thought to kill cells that were no longer wanted, such as those in the tails of [[tadpole]]s or in the web from the fingers of a 3- to 6-month-old [[fetus]]. While lysosomes digest some materials in this process, it is actually accomplished through programmed cell death, called [[apoptosis]].<ref>[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/L/Lysosomes.html Lysosomes and Peroxisomes<!-- Bot generated title -->]</ref><ref>Mader, Sylvia. (2007). Biology 9th ed. McGraw Hill. New York. ISBN 978-0072464634</ref> |
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Originally, De Duve had termed the organelles the "suicide bags" or "suicide sacs" of the cells, for their hypothesized role in [[apoptosis]].<ref>Hayashi, Teru, and others. "Subcellular Particles." ''Subcellular Particles.'', 1959.</ref> However, it has since been concluded that they only play a minor role in [[cell death]].<ref>{{cite journal | vauthors = Turk B, Turk V | title = Lysosomes as "suicide bags" in cell death: myth or reality? | journal = The Journal of Biological Chemistry | volume = 284 | issue = 33 | pages = 21783–21787 | date = August 2009 | pmid = 19473965 | pmc = 2755904 | doi = 10.1074/jbc.R109.023820 | doi-access = free }}</ref> |
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==Clinical relevance== |
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There are a number of illnesses that are caused by the malfunction of the lysosomes or one of their digestive proteins, e.g., [[Tay-Sachs disease]], or [[Pompe's disease]]. These are caused by a defective or missing digestive protein, which leads to the accumulation of substrates within the cell, impairing [[metabolism]]. |
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== Function and structure == |
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In the broad sense, these can be classified as [[mucopolysaccharidosis|mucopolysaccharidoses]], [[GM2 gangliosidosis|GM<sub>2</sub> gangliosidoses]], [[lipid storage disorder]]s, [[glycoproteinosis|glycoproteinoses]], [[mucolipidosis|mucolipidoses]], or [[leukodystrophy|leukodystrophies]]. |
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Lysosomes contain a variety of enzymes, enabling the cell to break down various biomolecules it engulfs, including [[peptides]], [[nucleic acid]]s, [[carbohydrate]]s, and [[lipid]]s ([[lysosomal lipase]]). The enzymes responsible for this hydrolysis require an acidic environment for optimal activity. |
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==Additional images== |
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<gallery> |
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Image:Localisations02eng.jpg|Proteins in different [[cellular compartment]]s and structures tagged with [[green fluorescent protein]]. |
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</gallery> |
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In addition to being able to break down polymers, lysosomes are capable of fusing with other organelles & digesting large structures or cellular debris; through cooperation with [[phagosome]]s, they are able to conduct [[autophagy]], clearing out damaged structures. Similarly, they are able to break down virus particles or bacteria in [[phagocytosis]] of [[macrophage]]s. |
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==External links== |
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* [http://opm.phar.umich.edu/localization.php?localization=Lysosome%20membrane 3D structures of proteins associated with lysosome membrane] |
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The size of lysosomes varies from 0.1 [[micrometre|μm]] to 1.2 [[micrometre|μm]].<ref>{{cite book | vauthors = Kuehnel W | title=Color Atlas of Cytology, Histology, & Microscopic Anatomy | publisher=Thieme | year=2003 | edition=4th | pages=34 | isbn=978-1-58890-175-0 }}</ref> With a [[pH]] ranging from ~4.5–5.0, the interior of the lysosomes is acidic compared to the slightly basic [[cytosol]] (pH 7.2). The lysosomal membrane protects the cytosol, and therefore the rest of the [[cell (biology)|cell]], from the [[degradative enzyme]]s within the lysosome. The cell is additionally protected from any lysosomal acid [[hydrolases]] that drain into the cytosol, as these enzymes are pH-sensitive and do not function well or at all in the alkaline environment of the cytosol. This ensures that cytosolic molecules and organelles are not destroyed in case there is leakage of the hydrolytic enzymes from the lysosome. |
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==References== |
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<references /> |
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The lysosome maintains its pH differential by pumping in [[proton]]s (H<sup>+</sup> ions) from the cytosol across the [[Cell membrane|membrane]] via [[proton pump]]s and [[chloride channel|chloride ion channel]]s. [[V-ATPase|Vacuolar-ATPase]]s are responsible for transport of protons, while the counter transport of chloride ions is performed by [[CLCN7|ClC-7]] Cl<sup>−</sup>/H<sup>+</sup> antiporter. In this way a steady acidic environment is maintained.<ref name="Lysosomal acidification mechanisms">{{cite journal | vauthors = Mindell JA | title = Lysosomal acidification mechanisms | journal = Annual Review of Physiology | volume = 74 | issue = 1 | pages = 69–86 | year = 2012 | pmid = 22335796 | doi = 10.1146/annurev-physiol-012110-142317 | url = https://zenodo.org/record/894445 }}</ref><ref>{{cite journal | vauthors = Ishida Y, Nayak S, Mindell JA, Grabe M | title = A model of lysosomal pH regulation | journal = The Journal of General Physiology | volume = 141 | issue = 6 | pages = 705–720 | date = June 2013 | pmid = 23712550 | pmc = 3664703 | doi = 10.1085/jgp.201210930 }}</ref> |
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It sources its versatile capacity for degradation by import of enzymes with specificity for different substrates; [[cathepsin]]s are the major class of hydrolytic enzymes, while [[Acid alpha-glucosidase|lysosomal alpha-glucosidase]] is responsible for carbohydrates, and [[ACP2|lysosomal acid phosphatase]] is necessary to release phosphate groups of phospholipids. |
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Recent research also indicates that lysosomes can act as a source of intracellular calcium.<ref>{{cite journal | vauthors = Medina DL, Di Paola S, Peluso I, Armani A, De Stefani D, Venditti R, Montefusco S, Scotto-Rosato A, Prezioso C, Forrester A, Settembre C, Wang W, Gao Q, Xu H, Sandri M, Rizzuto R, De Matteis MA, Ballabio A | display-authors = 6 | title = Lysosomal calcium signalling regulates autophagy through calcineurin and TFEB | journal = Nature Cell Biology | volume = 17 | issue = 3 | pages = 288–299 | date = March 2015 | pmid = 25720963 | pmc = 4801004 | doi = 10.1038/ncb3114 }}</ref> |
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== Formation == |
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[[File:Endocytic pathway of animal cells showing EGF receptors, transferrin receptors and mannose-6-phosphate receptors.jpg|alt=This is crucial for many disease pathways|thumb|The lysosome is shown in purple, as an endpoint in endocytotic sorting. AP2 is necessary for vesicle formation, whereas the mannose-6-receptor is necessary for sorting hydrolase into the lysosome's lumen.]] |
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Many components of animal cells are recycled by transferring them inside or embedded in sections of membrane. For instance, in [[endocytosis]] (more specifically, [[macropinocytosis]]), a portion of the cell's plasma membrane pinches off to form vesicles that will eventually fuse with an organelle within the cell. Without active replenishment, the plasma membrane would continuously decrease in size. It is thought that lysosomes participate in this dynamic membrane exchange system and are formed by a gradual maturation process from [[endosomes]].<ref name=Alberts>{{cite book| vauthors = Alberts B | title = Molecular biology of the cell|year=2002|publisher=Garland Science|location=New York|isbn=978-0-8153-3218-3|edition=4th|display-authors=etal}}</ref><ref name="endo18">{{cite journal | vauthors = Falcone S, Cocucci E, Podini P, Kirchhausen T, Clementi E, Meldolesi J | title = Macropinocytosis: regulated coordination of endocytic and exocytic membrane traffic events | journal = Journal of Cell Science | volume = 119 | issue = Pt 22 | pages = 4758–4769 | date = November 2006 | pmid = 17077125 | doi = 10.1242/jcs.03238 | doi-access = }}</ref> |
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The production of lysosomal proteins suggests one method of lysosome sustainment. Lysosomal protein genes are transcribed in the [[Cell nucleus|nucleus]] in a process that is controlled by transcription factor EB ([[TFEB]]).<ref name="pmid19556463"/> mRNA transcripts exit the nucleus into the cytosol, where they are translated by [[ribosomes]]. The nascent peptide chains are [[Protein targeting#Protein translocation|translocated]] into the rough [[endoplasmic reticulum]], where they are modified. Lysosomal soluble proteins exit the endoplasmic reticulum via [[COPII]]-coated vesicles after recruitment by the [[EGRESS complex]] ('''E'''R-to-'''G'''olgi '''r'''elaying of '''e'''nzymes of the ly'''s'''osomal '''s'''ystem), which is composed of [[CLN6]] and [[CLN8]] proteins.<ref name="di Ronza, A. 2018"/><ref name="pmid32597833"/> COPII vesicles then deliver lysosomal enzymes to the [[Golgi apparatus]], where a specific lysosomal tag, [[mannose 6-phosphate]], is added to the peptides. The presence of these tags allow for binding to [[mannose 6-phosphate receptor]]s in the Golgi apparatus, a phenomenon that is crucial for proper packaging into vesicles destined for the lysosomal system.<ref name=Lodish>{{cite book| vauthors = Lodish H |title=Molecular cell biology|year=2000|publisher=Scientific American Books|location=New York|isbn=978-0-7167-3136-8|edition=4th|display-authors=etal|url-access=registration|url=https://archive.org/details/molecularcellbio00lodi}}</ref> |
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Upon leaving the Golgi apparatus, the lysosomal enzyme-filled vesicle fuses with a [[Endosome#Types|late endosome]], a relatively acidic organelle with an approximate pH of 5.5. This acidic environment causes dissociation of the lysosomal enzymes from the mannose 6-phosphate receptors. The enzymes are packed into vesicles for further transport to established lysosomes.<ref name=Lodish /> The late endosome itself can eventually grow into a mature lysosome, as evidenced by the transport of endosomal membrane components from the lysosomes back to the endosomes.<ref name=Alberts /> |
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== Pathogen entry == |
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As the endpoint of endocytosis, the lysosome also acts as a safeguard in preventing pathogens from being able to reach the cytoplasm before being degraded. Pathogens often hijack endocytotic pathways such as [[pinocytosis]] in order to gain entry into the cell. The lysosome prevents easy entry into the cell by hydrolyzing the biomolecules of pathogens necessary for their replication strategies; reduced lysosomal activity results in an increase in viral infectivity, including HIV.<ref name="Wei, Bangdong L. 2005">{{cite journal | vauthors = Wei BL, Denton PW, O'Neill E, Luo T, Foster JL, Garcia JV | title = Inhibition of lysosome and proteasome function enhances human immunodeficiency virus type 1 infection | journal = Journal of Virology | volume = 79 | issue = 9 | pages = 5705–5712 | date = May 2005 | pmid = 15827185 | pmc = 1082736 | doi = 10.1128/jvi.79.9.5705-5712.2005 }}</ref> In addition, [[AB5 toxin|AB<sub>5</sub>]] toxins such as [[Cholera toxin|cholera]] hijack the endosomal pathway while evading lysosomal degradation.<ref name="Wei, Bangdong L. 2005"/> |
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==Clinical significance== |
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Lysosomes are involved in a group of genetically inherited deficiencies, or mutations called [[lysosomal storage diseases]] (LSD), [[inborn errors of metabolism]] caused by a dysfunction of one of the enzymes. The rate of incidence is estimated to be 1 in 5,000 births, and the true figure expected to be higher as many cases are likely to be undiagnosed or misdiagnosed. The primary cause is deficiency of an [[acid hydrolase]]. Other conditions are due to defects in lysosomal membrane proteins that fail to transport the enzyme, non-enzymatic soluble lysosomal proteins. The initial effect of such disorders is accumulation of specific macromolecules or monomeric compounds inside the endosomal–autophagic–lysosomal system.<ref name=platt/> This results in abnormal signaling pathways, [[calcium homeostasis]], [[Lipid synthesis|lipid biosynthesis]] and degradation and intracellular trafficking, ultimately leading to pathogenetic disorders. The organs most affected are [[Central nervous system|brain]], [[viscera]], bone and [[cartilage]].<ref>{{cite journal | vauthors = Schultz ML, Tecedor L, Chang M, Davidson BL | title = Clarifying lysosomal storage diseases | journal = Trends in Neurosciences | volume = 34 | issue = 8 | pages = 401–410 | date = August 2011 | pmid = 21723623 | pmc = 3153126 | doi = 10.1016/j.tins.2011.05.006 }}</ref><ref>{{cite journal | vauthors = Lieberman AP, Puertollano R, Raben N, Slaugenhaupt S, Walkley SU, Ballabio A | title = Autophagy in lysosomal storage disorders | journal = Autophagy | volume = 8 | issue = 5 | pages = 719–730 | date = May 2012 | pmid = 22647656 | pmc = 3378416 | doi = 10.4161/auto.19469 }}</ref> |
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There is no direct medical treatment to cure LSDs.<ref>.{{cite journal | vauthors = Parenti G, Pignata C, Vajro P, Salerno M | title = New strategies for the treatment of lysosomal storage diseases (review) | journal = International Journal of Molecular Medicine | volume = 31 | issue = 1 | pages = 11–20 | date = January 2013 | pmid = 23165354 | doi = 10.3892/ijmm.2012.1187 | doi-access = free }}</ref> The most common LSD is [[Gaucher's disease]], which is due to deficiency of the enzyme [[glucocerebrosidase]]. Consequently, the enzyme substrate, the fatty acid [[glucosylceramide]] accumulates, particularly in [[white blood cells]], which in turn affects spleen, liver, kidneys, lungs, brain and bone marrow. The disease is characterized by bruises, fatigue, [[anaemia]], low blood platelets, [[osteoporosis]], and enlargement of the liver and spleen.<ref>{{cite journal | vauthors = Rosenbloom BE, Weinreb NJ | title = Gaucher disease: a comprehensive review | journal = Critical Reviews in Oncogenesis | volume = 18 | issue = 3 | pages = 163–175 | year = 2013 | pmid = 23510062 | doi = 10.1615/CritRevOncog.2013006060 }}</ref><ref>{{cite journal | vauthors = Sidransky E | title = Gaucher disease: insights from a rare Mendelian disorder | journal = Discovery Medicine | volume = 14 | issue = 77 | pages = 273–281 | date = October 2012 | pmid = 23114583 | pmc = 4141347 }}</ref> As of 2017, [[enzyme replacement therapy]] is available for treating 8 of the 50-60 known LDs.<ref name="Solomon">{{cite journal | vauthors = Solomon M, Muro S | title = Lysosomal enzyme replacement therapies: Historical development, clinical outcomes, and future perspectives | journal = Advanced Drug Delivery Reviews | volume = 118 | pages = 109–134 | date = September 2017 | pmid = 28502768 | pmc = 5828774 | doi = 10.1016/j.addr.2017.05.004 }}</ref> |
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The most severe and rarely found, lysosomal storage disease is [[inclusion cell disease]].<ref name="Alberts2004">{{cite book | vauthors = Alberts B |title=Molecular Biology of the Cell |publisher=Garland Science |isbn=978-0815340720 |page=744 |edition=4th|year=2002 }}</ref> |
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[[Metachromatic leukodystrophy]] is another lysosomal storage disease that also affects [[sphingolipid metabolism]]. |
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Dysfunctional lysosome activity is also heavily implicated in the biology of [[Ageing|aging]], and age-related diseases such as Alzheimer's, Parkinson's, and cardiovascular disease.<ref name="The crucial impact of lysosomes in"/><ref>{{cite journal | vauthors = Finkbeiner S | title = The Autophagy Lysosomal Pathway and Neurodegeneration | journal = Cold Spring Harbor Perspectives in Biology | volume = 12 | issue = 3 | pages = a033993 | date = March 2020 | pmid = 30936119 | pmc = 6773515 | doi = 10.1101/cshperspect.a033993 }}</ref> |
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== Different enzymes present in Lysosomes == |
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<ref>{{Cite book | vauthors = Kumar P, Mina U |title=Life Sciences: Fundamentals and practice. |date=2013|publisher=Pathfinder Academy |isbn=978-81-906427-0-5|edition=3rd|location=New Delhi|oclc=857764171}}</ref> |
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{| class="wikitable" |
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|+ |
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!Sr. No |
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!Enzymes |
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!Substrate |
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|- |
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|1 |
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|'''Phosphates''' |
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| |
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|- |
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| |
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|A- Acid phosphatase |
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|Most phosphomonoesters |
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|- |
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| |
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|B- Acid phosphodiesterase |
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|Oligonucleotides and phosphodiesterase |
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|- |
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| |
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| |
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| |
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|- |
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|2 |
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|'''Nucleases''' |
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| |
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|- |
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| |
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|A- Acid ribonuclease |
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|RNA |
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|- |
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| |
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|B- Acid deoxyribonuclease |
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|DNA |
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|- |
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| |
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| |
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| |
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|- |
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|3 |
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|'''Polysaccharides/ mucopolysaccharides hydrolyzing enzymes''' |
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| |
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|- |
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| |
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|A- β-Galactosidase |
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|Galactosides |
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|- |
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| |
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|B- α'''-'''Glucosidase |
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|Glycogen |
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|- |
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| |
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|C- α'''-'''Mannosidase |
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|Mannosides, glycoproteins |
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|- |
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| |
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|D- β- Glucoronidase |
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|Polysaccharides and mucopolysaccharides |
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|- |
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| |
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|E- Lysozymes |
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|Bacterial cell walls and mucopolysaccharides |
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|- |
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| |
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|F- Hyaluronidase |
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|Hyaluronic acids, chondroitin sulfates |
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|- |
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| |
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|H- Arylsulphatase |
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|Organic sulfates |
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|- |
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| |
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| |
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| |
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|- |
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|4 |
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|'''Proteases''' |
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| |
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|- |
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| |
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|A- Cathepsin(s) |
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|Proteins |
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|- |
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| |
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|B- Collagenase |
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|Collagen |
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|- |
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| |
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|C- Peptidase |
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|Peptides |
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|- |
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| |
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| |
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| |
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|- |
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|5 |
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|'''Lipid degrading enzymes''' |
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| |
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|- |
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| |
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|A- Esterase |
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|Fatty acyl esters |
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|- |
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| |
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|B- Phospholipase |
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|Phospholipids |
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|- |
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| |
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| |
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| |
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|- |
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|6 |
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|'''Sulfatases''' |
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| |
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|- |
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| |
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|A- Arylsulfatase(A, B & G) |
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|O- and N-Sulfate esters |
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|- |
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| |
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|B- Glucosamine (N-acetyl)-6-Sulfatase/GNS |
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|Glycosaminoglycans |
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|- |
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| |
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|C- Iduronate 2-Sulfatase/IDS |
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|O- and N-Sulfate esters |
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|} |
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===Lysosomotropism=== |
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Weak [[Base (chemistry)|bases]] with [[Lipophilicity|lipophilic]] properties accumulate in acidic intracellular compartments like lysosomes. While the plasma and lysosomal membranes are permeable for neutral and uncharged species of weak bases, the charged protonated species of weak bases do not permeate biomembranes and accumulate within lysosomes. The concentration within lysosomes may reach levels 100 to 1000 fold higher than extracellular concentrations. This phenomenon is called [[wikt:lysosomotropism|lysosomotropism]],<ref>{{cite journal | vauthors = de Duve C, de Barsy T, Poole B, Trouet A, Tulkens P, Van Hoof F | title = Commentary. Lysosomotropic agents | journal = Biochemical Pharmacology | volume = 23 | issue = 18 | pages = 2495–2531 | date = September 1974 | pmid = 4606365 | doi = 10.1016/0006-2952(74)90174-9 }}</ref> "acid trapping" or "proton pump" effect.<ref>{{cite book | vauthors = Traganos F, Darzynkiewicz Z | title = Lysosomal proton pump activity: supravital cell staining with acridine orange differentiates leukocyte subpopulations | chapter = Chapter 12 Lysosomal Proton Pump Activity: Supravital Cell Staining with Acridine Orange Differentiates Leukocyte Subpopulations | series = Methods in Cell Biology | volume = 41 | pages = 185–194 | year = 1994 | pmid = 7532261 | doi = 10.1016/S0091-679X(08)61717-3 | isbn = 978-0-12-564142-5 }}</ref> The amount of accumulation of lysosomotropic compounds may be estimated using a cell-based mathematical model.<ref>{{cite journal | vauthors = Trapp S, Rosania GR, Horobin RW, Kornhuber J | title = Quantitative modeling of selective lysosomal targeting for drug design | journal = European Biophysics Journal | volume = 37 | issue = 8 | pages = 1317–1328 | date = October 2008 | pmid = 18504571 | pmc = 2711917 | doi = 10.1007/s00249-008-0338-4 }}</ref> |
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A significant part of the clinically approved drugs are lipophilic weak bases with lysosomotropic properties. This explains a number of pharmacological properties of these drugs, such as high tissue-to-blood concentration gradients or long tissue elimination half-lives; these properties have been found for drugs such as [[haloperidol]],<ref>{{cite journal | vauthors = Kornhuber J, Schultz A, Wiltfang J, Meineke I, Gleiter CH, Zöchling R, Boissl KW, Leblhuber F, Riederer P | display-authors = 6 | title = Persistence of haloperidol in human brain tissue | journal = The American Journal of Psychiatry | volume = 156 | issue = 6 | pages = 885–890 | date = June 1999 | pmid = 10360127 | doi = 10.1176/ajp.156.6.885 | s2cid = 7258546 }}</ref> [[levomepromazine]],<ref>{{cite journal | vauthors = Kornhuber J, Weigmann H, Röhrich J, Wiltfang J, Bleich S, Meineke I, Zöchling R, Härtter S, Riederer P, Hiemke C | display-authors = 6 | title = Region specific distribution of levomepromazine in the human brain | journal = Journal of Neural Transmission | volume = 113 | issue = 3 | pages = 387–397 | date = March 2006 | pmid = 15997416 | doi = 10.1007/s00702-005-0331-3 | s2cid = 24735371 }}</ref> and [[amantadine]].<ref>{{cite journal | vauthors = Kornhuber J, Quack G, Danysz W, Jellinger K, Danielczyk W, Gsell W, Riederer P | title = Therapeutic brain concentration of the NMDA receptor antagonist amantadine | journal = Neuropharmacology | volume = 34 | issue = 7 | pages = 713–721 | date = July 1995 | pmid = 8532138 | doi = 10.1016/0028-3908(95)00056-c | s2cid = 25784783 }}</ref> However, high tissue concentrations and long elimination half-lives are explained also by lipophilicity and absorption of drugs to fatty tissue structures. Important lysosomal enzymes, such as acid sphingomyelinase, may be inhibited by lysosomally accumulated drugs.<ref>{{cite journal | vauthors = Kornhuber J, Tripal P, Reichel M, Terfloth L, Bleich S, Wiltfang J, Gulbins E | title = Identification of new functional inhibitors of acid sphingomyelinase using a structure-property-activity relation model | journal = Journal of Medicinal Chemistry | volume = 51 | issue = 2 | pages = 219–237 | date = January 2008 | pmid = 18027916 | doi = 10.1021/jm070524a | citeseerx = 10.1.1.324.8854 }}</ref><ref>{{cite journal | vauthors = Kornhuber J, Muehlbacher M, Trapp S, Pechmann S, Friedl A, Reichel M, Mühle C, Terfloth L, Groemer TW, Spitzer GM, Liedl KR, Gulbins E, Tripal P | display-authors = 6 | title = Identification of novel functional inhibitors of acid sphingomyelinase | journal = PLOS ONE | volume = 6 | issue = 8 | pages = e23852 | year = 2011 | pmid = 21909365 | pmc = 3166082 | doi = 10.1371/journal.pone.0023852 | veditors = Riezman H | doi-access = free | bibcode = 2011PLoSO...623852K }}</ref> Such compounds are termed FIASMAs (functional inhibitor of acid sphingomyelinase)<ref>{{cite journal | vauthors = Kornhuber J, Tripal P, Reichel M, Mühle C, Rhein C, Muehlbacher M, Groemer TW, Gulbins E | display-authors = 6 | title = Functional Inhibitors of Acid Sphingomyelinase (FIASMAs): a novel pharmacological group of drugs with broad clinical applications | journal = Cellular Physiology and Biochemistry | volume = 26 | issue = 1 | pages = 9–20 | year = 2010 | pmid = 20502000 | doi = 10.1159/000315101 | doi-access = }}</ref> and include for example [[fluoxetine]], [[sertraline]], or [[amitriptyline]]. |
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[[Ambroxol]] is a lysosomotropic drug of clinical use to treat conditions of productive cough for its mucolytic action. Ambroxol triggers the exocytosis of lysosomes via neutralization of lysosomal pH and [[Calcium channel opener|calcium release]] from acidic calcium stores.<ref>{{cite journal | vauthors = Fois G, Hobi N, Felder E, Ziegler A, Miklavc P, Walther P, Radermacher P, Haller T, Dietl P | display-authors = 6 | title = A new role for an old drug: Ambroxol triggers lysosomal exocytosis via pH-dependent Ca²⁺ release from acidic Ca²⁺ stores | journal = Cell Calcium | volume = 58 | issue = 6 | pages = 628–637 | date = December 2015 | pmid = 26560688 | doi = 10.1016/j.ceca.2015.10.002 }}</ref> Presumably for this reason, [[Ambroxol]] was also found to improve cellular function in some disease of lysosomal origin such as [[Parkinson's disease|Parkinson]]'s or [[lysosomal storage disease]].<ref>{{cite journal | vauthors = Albin RL, Dauer WT | title = Magic shotgun for Parkinson's disease? | journal = Brain | volume = 137 | issue = Pt 5 | pages = 1274–1275 | date = May 2014 | pmid = 24771397 | doi = 10.1093/brain/awu076 | doi-access = free }}</ref><ref>{{cite journal | vauthors = McNeill A, Magalhaes J, Shen C, Chau KY, Hughes D, Mehta A, Foltynie T, Cooper JM, Abramov AY, Gegg M, Schapira AH | display-authors = 6 | title = Ambroxol improves lysosomal biochemistry in glucocerebrosidase mutation-linked Parkinson disease cells | journal = Brain | volume = 137 | issue = Pt 5 | pages = 1481–1495 | date = May 2014 | pmid = 24574503 | pmc = 3999713 | doi = 10.1093/brain/awu020 }}</ref> |
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=== Systemic lupus erythematosus === |
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Impaired lysosome function is prominent in systemic lupus erythematosus preventing macrophages and monocytes from degrading neutrophil extracellular traps<ref>{{cite journal | vauthors = Hakkim A, Fürnrohr BG, Amann K, Laube B, Abed UA, Brinkmann V, Herrmann M, Voll RE, Zychlinsky A | display-authors = 6 | title = Impairment of neutrophil extracellular trap degradation is associated with lupus nephritis | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 107 | issue = 21 | pages = 9813–9818 | date = May 2010 | pmid = 20439745 | pmc = 2906830 | doi = 10.1073/pnas.0909927107 | doi-access = free | bibcode = 2010PNAS..107.9813H }}</ref> and immune complexes.<ref name=":0">{{cite journal | vauthors = Monteith AJ, Kang S, Scott E, Hillman K, Rajfur Z, Jacobson K, Costello MJ, Vilen BJ | display-authors = 6 | title = Defects in lysosomal maturation facilitate the activation of innate sensors in systemic lupus erythematosus | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 113 | issue = 15 | pages = E2142–E2151 | date = April 2016 | pmid = 27035940 | pmc = 4839468 | doi = 10.1073/pnas.1513943113 | doi-access = free | bibcode = 2016PNAS..113E2142M }}</ref><ref>{{cite journal | vauthors = Kavai M, Szegedi G | title = Immune complex clearance by monocytes and macrophages in systemic lupus erythematosus | journal = Autoimmunity Reviews | volume = 6 | issue = 7 | pages = 497–502 | date = August 2007 | pmid = 17643939 | doi = 10.1016/j.autrev.2007.01.017 }}</ref><ref name="pmid3787186">{{cite journal | vauthors = Kávai M, Csipö I, Sonkoly I, Csongor J, Szegedi GY | title = Defective immune complex degradation by monocytes in patients with systemic lupus erythematosus | journal = Scandinavian Journal of Immunology | volume = 24 | issue = 5 | pages = 527–532 | date = November 1986 | pmid = 3787186 | doi = 10.1111/j.1365-3083.1986.tb02167.x | s2cid = 23685272 }}</ref> The failure to degrade internalized immune complexes stems from chronic mTORC2 activity, which impairs lysosome acidification.<ref>{{cite journal | vauthors = Monteith AJ, Vincent HA, Kang S, Li P, Claiborne TM, Rajfur Z, Jacobson K, Moorman NJ, Vilen BJ | display-authors = 6 | title = mTORC2 Activity Disrupts Lysosome Acidification in Systemic Lupus Erythematosus by Impairing Caspase-1 Cleavage of Rab39a | journal = Journal of Immunology | volume = 201 | issue = 2 | pages = 371–382 | date = July 2018 | pmid = 29866702 | pmc = 6039264 | doi = 10.4049/jimmunol.1701712 }}</ref> As a result, immune complexes in the lysosome recycle to the surface of macrophages causing an accumulation of nuclear antigens upstream of multiple lupus-associated pathologies.<ref name=":0" /><ref>{{cite journal | vauthors = Kang S, Rogers JL, Monteith AJ, Jiang C, Schmitz J, Clarke SH, Tarrant TK, Truong YK, Diaz M, Fedoriw Y, Vilen BJ | display-authors = 6 | title = Apoptotic Debris Accumulates on Hematopoietic Cells and Promotes Disease in Murine and Human Systemic Lupus Erythematosus | journal = Journal of Immunology | volume = 196 | issue = 10 | pages = 4030–4039 | date = May 2016 | pmid = 27059595 | pmc = 4868781 | doi = 10.4049/jimmunol.1500418 }}</ref><ref>{{cite journal | vauthors = Kang S, Fedoriw Y, Brenneman EK, Truong YK, Kikly K, Vilen BJ | title = BAFF Induces Tertiary Lymphoid Structures and Positions T Cells within the Glomeruli during Lupus Nephritis | journal = Journal of Immunology | volume = 198 | issue = 7 | pages = 2602–2611 | date = April 2017 | pmid = 28235864 | pmc = 5360485 | doi = 10.4049/jimmunol.1600281 }}</ref> |
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== Controversy in botany == |
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By scientific convention, the term lysosome is applied to these vesicular organelles only in animals, and the term [[vacuole]] is applied to those in plants, fungi and algae (some animal cells also have vacuoles). Discoveries in plant cells since the 1970s started to challenge this definition. Plant vacuoles are found to be much more diverse in structure and function than previously thought.<ref>{{cite journal | vauthors = Marty F | title = Plant vacuoles | journal = The Plant Cell | volume = 11 | issue = 4 | pages = 587–600 | date = April 1999 | pmid = 10213780 | pmc = 144210 | doi = 10.2307/3870886 | jstor = 3870886 }}</ref><ref>{{cite journal | vauthors = Samaj J, Read ND, Volkmann D, Menzel D, Baluska F | title = The endocytic network in plants | journal = Trends in Cell Biology | volume = 15 | issue = 8 | pages = 425–433 | date = August 2005 | pmid = 16006126 | doi = 10.1016/j.tcb.2005.06.006 }}</ref> Some vacuoles contain their own hydrolytic enzymes and perform the classic lysosomal activity, which is autophagy.<ref>{{cite journal| vauthors = Matile P |title=Biochemistry and Function of Vacuoles|journal=Annual Review of Plant Physiology|year=1978|volume=29|issue=1|pages=193–213|doi=10.1146/annurev.pp.29.060178.001205}}</ref><ref>{{cite journal | vauthors = Moriyasu Y, Ohsumi Y | title = Autophagy in Tobacco Suspension-Cultured Cells in Response to Sucrose Starvation | journal = Plant Physiology | volume = 111 | issue = 4 | pages = 1233–1241 | date = August 1996 | pmid = 12226358 | pmc = 161001 | doi = 10.1104/pp.111.4.1233 }}</ref><ref>{{cite journal | vauthors = Jiao BB, Wang JJ, Zhu XD, Zeng LJ, Li Q, He ZH | title = A novel protein RLS1 with NB-ARM domains is involved in chloroplast degradation during leaf senescence in rice | journal = Molecular Plant | volume = 5 | issue = 1 | pages = 205–217 | date = January 2012 | pmid = 21980143 | doi = 10.1093/mp/ssr081 | doi-access = free }}</ref> These vacuoles are therefore seen as fulfilling the role of the animal lysosome. Based on de Duve's description that "only when considered as part of a system involved directly or indirectly in intracellular digestion does the term lysosome describe a physiological unit", some botanists strongly argued that these vacuoles are lysosomes.<ref>{{cite journal | vauthors = Swanson SJ, Bethke PC, Jones RL | title = Barley aleurone cells contain two types of vacuoles. Characterization Of lytic organelles by use of fluorescent probes | journal = The Plant Cell | volume = 10 | issue = 5 | pages = 685–698 | date = May 1998 | pmid = 9596630 | pmc = 144374 | doi = 10.2307/3870657 | jstor = 3870657 }}</ref> However, this is not universally accepted as the vacuoles are strictly not similar to lysosomes, such as in their specific enzymes and lack of phagocytic functions.<ref>{{cite book| vauthors = Holtzman E | title = Lysosomes|year=1989|publisher=Plenum Press|location=New York|isbn=978-0306-4-3126-5|pages=7, 15}}</ref> Vacuoles do not have catabolic activity and do not undergo [[exocytosis]] as lysosomes do.<ref>{{cite book| vauthors = De DN | title = Plant Cell Vacuoles: An Introduction | year = 2000 | publisher = Csiro Publishing | location = Australia | isbn =978-0-643-09944-9 | url = https://books.google.com/books?id=o5H13nnYXngC}}</ref> |
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== See also == |
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* [[Peroxisome]] |
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* [[Cathelicidin]] |
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* [[Antimicrobial peptides]] |
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* [[Innate immune system]] |
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* [[TMEM106B]] |
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== References == |
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{{Reflist|33em}} |
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== External links == |
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{{wiktionary}} |
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* {{NCBI-scienceprimer}} |
* {{NCBI-scienceprimer}} |
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* [http://opm.phar.umich.edu/localization.php?localization=Lysosome%20membrane 3D structures of proteins associated with lysosome membrane] |
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* [http://www.hideandseek.org Hide and Seek Foundation For Lysosomal Research] |
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*[http://www.lysosomaldiseasenetwork.org/ Lysosomal Disease Network, a research consortium funded by the NIH through its NCATS/Rare Diseases Clinical Research Network] |
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* [https://www.nytimes.com/2009/10/06/science/06cell.html Self-Destructive Behavior in Cells May Hold Key to a Longer Life] |
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* [http://content.nejm.org/cgi/content/full/NEJMoa0902630 Mutations in the Lysosomal Enzyme–Targeting Pathway and Persistent Stuttering] |
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* [http://highered.mcgraw-hill.com/olc/dl/120067/bio01.swf Animation showing how lysosomes are made, and their function] |
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{{organelles}} |
{{organelles}} |
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{{Authority control}} |
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[[Category:Organelles]] |
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[[Category:Vesicles]] |
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[[ar:جسيم حال]] |
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[[Category:Cell anatomy]] |
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[[id:Lisosom]] |
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[[Category:Eukaryotic cell anatomy]] |
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[[ca:Lisosoma]] |
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[[ |
[[Category:Organelles]] |
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[[Category:Lysosomal storage diseases]] |
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[[da:Lysosom]] |
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[[de:Lysosom]] |
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[[el:Λυσόσωμα]] |
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[[es:Lisosoma]] |
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[[eo:Lizosomo]] |
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[[fa:لیزوزوم]] |
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[[fr:Lysosome]] |
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[[gl:Lisosoma]] |
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[[ko:리소좀]] |
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[[hr:Lizosom]] |
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[[it:Lisosoma]] |
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[[he:ליזוזום]] |
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[[lv:Lizosoma]] |
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[[lb:Lysosom]] |
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[[lt:Lizosomos]] |
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[[hu:Lizoszóma]] |
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[[mk:Лизозом]] |
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[[nl:Lysosoom]] |
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[[ja:リソソーム]] |
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[[no:Lysosom]] |
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[[oc:Lisosòma]] |
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[[pl:Lizosom]] |
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[[pt:Lisossomo]] |
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[[ro:Lizozom]] |
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[[ru:Лизосома]] |
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[[sk:Lyzozóm]] |
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[[sl:Lizosom]] |
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[[sr:Лизозом]] |
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[[sh:Lizozom]] |
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[[fi:Lysosomi]] |
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[[sv:Lysosom]] |
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[[vi:Lysosome]] |
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[[tr:Lizozom]] |
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[[uk:Лізосома]] |
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[[zh:溶體]] |
Latest revision as of 17:47, 13 December 2024
Cell biology | |
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Animal cell diagram | |
A lysosome (/ˈlaɪsəˌsoʊm/) is a single membrane-bound organelle found in many animal cells.[1][2] They are spherical vesicles that contain hydrolytic enzymes that digest many kinds of biomolecules. A lysosome has a specific composition, of both its membrane proteins and its lumenal proteins. The lumen's pH (~4.5–5.0)[3] is optimal for the enzymes involved in hydrolysis, analogous to the activity of the stomach. Besides degradation of polymers, the lysosome is involved in cell processes of secretion, plasma membrane repair, apoptosis, cell signaling, and energy metabolism.[4]
Lysosomes are degradative organelles that act as the waste disposal system of the cell by digesting used materials in the cytoplasm, from both inside and outside the cell. Material from outside the cell is taken up through endocytosis, while material from the inside of the cell is digested through autophagy.[6] The sizes of the organelles vary greatly—the larger ones can be more than 10 times the size of the smaller ones.[7] They were discovered and named by Belgian biologist Christian de Duve, who eventually received the Nobel Prize in Physiology or Medicine in 1974.
Lysosomes contain more than 60 different enzymes, and have more than 50 membrane proteins.[8][9] Enzymes of the lysosomes are synthesized in the rough endoplasmic reticulum and exported to the Golgi apparatus upon recruitment by a complex composed of CLN6 and CLN8 proteins.[10][11] The enzymes are transported from the Golgi apparatus to lysosomes in small vesicles, which fuse with larger acidic vesicles. Enzymes destined for a lysosome are tagged with the molecule mannose 6-phosphate, so that they are properly sorted into acidified vesicles.[12][13]
In 2009, Marco Sardiello and co-workers discovered that the synthesis of most lysosomal enzymes and membrane proteins is controlled by transcription factor EB (TFEB), which promotes the transcription of nuclear genes.[6][14] Mutations in the genes for these enzymes are responsible for more than 50 different human genetic disorders collectively known as lysosomal storage diseases. These diseases result in an accumulation of specific substrates, due to the inability to break them down. These genetic defects are related to several neurodegenerative disorders, cancers, cardiovascular diseases, and aging-related diseases.[15][16][17]
Etymology and pronunciation
[edit]The word lysosome (/ˈlaɪsoʊsoʊm/, /ˈlaɪzəzoʊm/) is Neo-Latin that uses the combining forms lyso- (referring to lysis and derived from the Latin lysis, meaning "to loosen", via Ancient Greek λύσις [lúsis]), and -some, from soma, "body", yielding "body that lyses" or "lytic body". The adjectival form is lysosomal. The forms *lyosome and *lyosomal are much rarer; they use the lyo- form of the prefix but are often treated by readers and editors as mere unthinking replications of typos, which has no doubt been true as often as not.
Discovery
[edit]Christian de Duve, at the Laboratory of Physiological Chemistry at the Catholic University of Louvain in Belgium, had been studying the mechanism of action of insulin in liver cells. By 1949, he and his team had focused on the enzyme called glucose 6-phosphatase, which is the first crucial enzyme in sugar metabolism and the target of insulin. They already suspected that this enzyme played a key role in regulating blood sugar levels. However, even after a series of experiments, they failed to purify and isolate the enzyme from the cellular extracts. Therefore, they tried a more arduous procedure of cell fractionation, by which cellular components are separated based on their sizes using centrifugation.
They succeeded in detecting the enzyme activity from the microsomal fraction. This was the crucial step in the serendipitous discovery of lysosomes. To estimate this enzyme activity, they used that of the standardized enzyme acid phosphatase and found that the activity was only 10% of the expected value. One day, the enzyme activity of purified cell fractions which had been refrigerated for five days was measured. Surprisingly, the enzyme activity was increased to normal of that of the fresh sample. The result was the same no matter how many times they repeated the estimation, and led to the conclusion that a membrane-like barrier limited the accessibility of the enzyme to its substrate, and that the enzymes were able to diffuse after a few days (and react with their substrate). They described this membrane-like barrier as a "saclike structure surrounded by a membrane and containing acid phosphatase."[18]
It became clear that this enzyme from the cell fraction came from membranous fractions, which were definitely cell organelles, and in 1955 De Duve named them "lysosomes" to reflect their digestive properties.[19] The same year, Alex B. Novikoff from the University of Vermont visited de Duve's laboratory, and successfully obtained the first electron micrographs of the new organelle. Using a staining method for acid phosphatase, de Duve and Novikoff confirmed the location of the hydrolytic enzymes of lysosomes using light and electron microscopic studies.[20][21] de Duve won the Nobel Prize in Physiology or Medicine in 1974 for this discovery.
Originally, De Duve had termed the organelles the "suicide bags" or "suicide sacs" of the cells, for their hypothesized role in apoptosis.[22] However, it has since been concluded that they only play a minor role in cell death.[23]
Function and structure
[edit]Lysosomes contain a variety of enzymes, enabling the cell to break down various biomolecules it engulfs, including peptides, nucleic acids, carbohydrates, and lipids (lysosomal lipase). The enzymes responsible for this hydrolysis require an acidic environment for optimal activity.
In addition to being able to break down polymers, lysosomes are capable of fusing with other organelles & digesting large structures or cellular debris; through cooperation with phagosomes, they are able to conduct autophagy, clearing out damaged structures. Similarly, they are able to break down virus particles or bacteria in phagocytosis of macrophages.
The size of lysosomes varies from 0.1 μm to 1.2 μm.[24] With a pH ranging from ~4.5–5.0, the interior of the lysosomes is acidic compared to the slightly basic cytosol (pH 7.2). The lysosomal membrane protects the cytosol, and therefore the rest of the cell, from the degradative enzymes within the lysosome. The cell is additionally protected from any lysosomal acid hydrolases that drain into the cytosol, as these enzymes are pH-sensitive and do not function well or at all in the alkaline environment of the cytosol. This ensures that cytosolic molecules and organelles are not destroyed in case there is leakage of the hydrolytic enzymes from the lysosome.
The lysosome maintains its pH differential by pumping in protons (H+ ions) from the cytosol across the membrane via proton pumps and chloride ion channels. Vacuolar-ATPases are responsible for transport of protons, while the counter transport of chloride ions is performed by ClC-7 Cl−/H+ antiporter. In this way a steady acidic environment is maintained.[25][26]
It sources its versatile capacity for degradation by import of enzymes with specificity for different substrates; cathepsins are the major class of hydrolytic enzymes, while lysosomal alpha-glucosidase is responsible for carbohydrates, and lysosomal acid phosphatase is necessary to release phosphate groups of phospholipids.
Recent research also indicates that lysosomes can act as a source of intracellular calcium.[27]
Formation
[edit]Many components of animal cells are recycled by transferring them inside or embedded in sections of membrane. For instance, in endocytosis (more specifically, macropinocytosis), a portion of the cell's plasma membrane pinches off to form vesicles that will eventually fuse with an organelle within the cell. Without active replenishment, the plasma membrane would continuously decrease in size. It is thought that lysosomes participate in this dynamic membrane exchange system and are formed by a gradual maturation process from endosomes.[28][29]
The production of lysosomal proteins suggests one method of lysosome sustainment. Lysosomal protein genes are transcribed in the nucleus in a process that is controlled by transcription factor EB (TFEB).[14] mRNA transcripts exit the nucleus into the cytosol, where they are translated by ribosomes. The nascent peptide chains are translocated into the rough endoplasmic reticulum, where they are modified. Lysosomal soluble proteins exit the endoplasmic reticulum via COPII-coated vesicles after recruitment by the EGRESS complex (ER-to-Golgi relaying of enzymes of the lysosomal system), which is composed of CLN6 and CLN8 proteins.[10][11] COPII vesicles then deliver lysosomal enzymes to the Golgi apparatus, where a specific lysosomal tag, mannose 6-phosphate, is added to the peptides. The presence of these tags allow for binding to mannose 6-phosphate receptors in the Golgi apparatus, a phenomenon that is crucial for proper packaging into vesicles destined for the lysosomal system.[30]
Upon leaving the Golgi apparatus, the lysosomal enzyme-filled vesicle fuses with a late endosome, a relatively acidic organelle with an approximate pH of 5.5. This acidic environment causes dissociation of the lysosomal enzymes from the mannose 6-phosphate receptors. The enzymes are packed into vesicles for further transport to established lysosomes.[30] The late endosome itself can eventually grow into a mature lysosome, as evidenced by the transport of endosomal membrane components from the lysosomes back to the endosomes.[28]
Pathogen entry
[edit]As the endpoint of endocytosis, the lysosome also acts as a safeguard in preventing pathogens from being able to reach the cytoplasm before being degraded. Pathogens often hijack endocytotic pathways such as pinocytosis in order to gain entry into the cell. The lysosome prevents easy entry into the cell by hydrolyzing the biomolecules of pathogens necessary for their replication strategies; reduced lysosomal activity results in an increase in viral infectivity, including HIV.[31] In addition, AB5 toxins such as cholera hijack the endosomal pathway while evading lysosomal degradation.[31]
Clinical significance
[edit]Lysosomes are involved in a group of genetically inherited deficiencies, or mutations called lysosomal storage diseases (LSD), inborn errors of metabolism caused by a dysfunction of one of the enzymes. The rate of incidence is estimated to be 1 in 5,000 births, and the true figure expected to be higher as many cases are likely to be undiagnosed or misdiagnosed. The primary cause is deficiency of an acid hydrolase. Other conditions are due to defects in lysosomal membrane proteins that fail to transport the enzyme, non-enzymatic soluble lysosomal proteins. The initial effect of such disorders is accumulation of specific macromolecules or monomeric compounds inside the endosomal–autophagic–lysosomal system.[15] This results in abnormal signaling pathways, calcium homeostasis, lipid biosynthesis and degradation and intracellular trafficking, ultimately leading to pathogenetic disorders. The organs most affected are brain, viscera, bone and cartilage.[32][33]
There is no direct medical treatment to cure LSDs.[34] The most common LSD is Gaucher's disease, which is due to deficiency of the enzyme glucocerebrosidase. Consequently, the enzyme substrate, the fatty acid glucosylceramide accumulates, particularly in white blood cells, which in turn affects spleen, liver, kidneys, lungs, brain and bone marrow. The disease is characterized by bruises, fatigue, anaemia, low blood platelets, osteoporosis, and enlargement of the liver and spleen.[35][36] As of 2017, enzyme replacement therapy is available for treating 8 of the 50-60 known LDs.[37]
The most severe and rarely found, lysosomal storage disease is inclusion cell disease.[38]
Metachromatic leukodystrophy is another lysosomal storage disease that also affects sphingolipid metabolism.
Dysfunctional lysosome activity is also heavily implicated in the biology of aging, and age-related diseases such as Alzheimer's, Parkinson's, and cardiovascular disease.[17][39]
Different enzymes present in Lysosomes
[edit]Sr. No | Enzymes | Substrate |
---|---|---|
1 | Phosphates | |
A- Acid phosphatase | Most phosphomonoesters | |
B- Acid phosphodiesterase | Oligonucleotides and phosphodiesterase | |
2 | Nucleases | |
A- Acid ribonuclease | RNA | |
B- Acid deoxyribonuclease | DNA | |
3 | Polysaccharides/ mucopolysaccharides hydrolyzing enzymes | |
A- β-Galactosidase | Galactosides | |
B- α-Glucosidase | Glycogen | |
C- α-Mannosidase | Mannosides, glycoproteins | |
D- β- Glucoronidase | Polysaccharides and mucopolysaccharides | |
E- Lysozymes | Bacterial cell walls and mucopolysaccharides | |
F- Hyaluronidase | Hyaluronic acids, chondroitin sulfates | |
H- Arylsulphatase | Organic sulfates | |
4 | Proteases | |
A- Cathepsin(s) | Proteins | |
B- Collagenase | Collagen | |
C- Peptidase | Peptides | |
5 | Lipid degrading enzymes | |
A- Esterase | Fatty acyl esters | |
B- Phospholipase | Phospholipids | |
6 | Sulfatases | |
A- Arylsulfatase(A, B & G) | O- and N-Sulfate esters | |
B- Glucosamine (N-acetyl)-6-Sulfatase/GNS | Glycosaminoglycans | |
C- Iduronate 2-Sulfatase/IDS | O- and N-Sulfate esters |
Lysosomotropism
[edit]Weak bases with lipophilic properties accumulate in acidic intracellular compartments like lysosomes. While the plasma and lysosomal membranes are permeable for neutral and uncharged species of weak bases, the charged protonated species of weak bases do not permeate biomembranes and accumulate within lysosomes. The concentration within lysosomes may reach levels 100 to 1000 fold higher than extracellular concentrations. This phenomenon is called lysosomotropism,[41] "acid trapping" or "proton pump" effect.[42] The amount of accumulation of lysosomotropic compounds may be estimated using a cell-based mathematical model.[43]
A significant part of the clinically approved drugs are lipophilic weak bases with lysosomotropic properties. This explains a number of pharmacological properties of these drugs, such as high tissue-to-blood concentration gradients or long tissue elimination half-lives; these properties have been found for drugs such as haloperidol,[44] levomepromazine,[45] and amantadine.[46] However, high tissue concentrations and long elimination half-lives are explained also by lipophilicity and absorption of drugs to fatty tissue structures. Important lysosomal enzymes, such as acid sphingomyelinase, may be inhibited by lysosomally accumulated drugs.[47][48] Such compounds are termed FIASMAs (functional inhibitor of acid sphingomyelinase)[49] and include for example fluoxetine, sertraline, or amitriptyline.
Ambroxol is a lysosomotropic drug of clinical use to treat conditions of productive cough for its mucolytic action. Ambroxol triggers the exocytosis of lysosomes via neutralization of lysosomal pH and calcium release from acidic calcium stores.[50] Presumably for this reason, Ambroxol was also found to improve cellular function in some disease of lysosomal origin such as Parkinson's or lysosomal storage disease.[51][52]
Systemic lupus erythematosus
[edit]Impaired lysosome function is prominent in systemic lupus erythematosus preventing macrophages and monocytes from degrading neutrophil extracellular traps[53] and immune complexes.[54][55][56] The failure to degrade internalized immune complexes stems from chronic mTORC2 activity, which impairs lysosome acidification.[57] As a result, immune complexes in the lysosome recycle to the surface of macrophages causing an accumulation of nuclear antigens upstream of multiple lupus-associated pathologies.[54][58][59]
Controversy in botany
[edit]By scientific convention, the term lysosome is applied to these vesicular organelles only in animals, and the term vacuole is applied to those in plants, fungi and algae (some animal cells also have vacuoles). Discoveries in plant cells since the 1970s started to challenge this definition. Plant vacuoles are found to be much more diverse in structure and function than previously thought.[60][61] Some vacuoles contain their own hydrolytic enzymes and perform the classic lysosomal activity, which is autophagy.[62][63][64] These vacuoles are therefore seen as fulfilling the role of the animal lysosome. Based on de Duve's description that "only when considered as part of a system involved directly or indirectly in intracellular digestion does the term lysosome describe a physiological unit", some botanists strongly argued that these vacuoles are lysosomes.[65] However, this is not universally accepted as the vacuoles are strictly not similar to lysosomes, such as in their specific enzymes and lack of phagocytic functions.[66] Vacuoles do not have catabolic activity and do not undergo exocytosis as lysosomes do.[67]
See also
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External links
[edit]- This article incorporates public domain material from Science Primer. NCBI. Archived from the original on 8 December 2009.
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