Serine

Serine (abbreviated as Ser or S) is an organic compound with the formula HO₂CCH(NH₂)CH₂OH. It is one of the 20 naturally occurring proteinogenic amino acids. Its codons are UCU, UCC, UCA, UCG, AGU and AGC. Only the L-stereoisomer appears naturally in proteins. It is not essential to the human diet, since it is synthesized in the body from other metabolites, including glycine. Serine was first obtained from silk protein, a particularly rich source, in 1865. Its name is derived from the Latin for silk, sericum. Serine's structure was established in 1902. The hydroxyl group attached makes it a polar amino acid.

Biosynthesis

The synthesis of serine starts with the oxidation of 3-phosphoglycerate forming 3-phosphohydroxypyruvate and NADH. Reductive amination of this ketone followed by hydrolysis affords serine. Serine hydroxymethyltransferase catalyzes the reversible, simultaneous conversions of L-serine to glycine (retro-aldol cleavage) and 5,6,7,8-tetrahydrofolate to 5,10-methylenetetrahydrofolate (hydrolysis).

Function

Metabolic

Serine is important in metabolism in that it participates in the biosynthesis of purines and pyrimidines. It is also the precursor to several amino acids, including glycine, cysteine, tryptophan (in bacteria). It is also the precursor to numerous of other metabolites, including sphingolipids. Serine is also a precursor to folate, which is the principal donor of one carbon fragments in biosynthesis.

Structural

Serine plays an important role in the catalytic function of many enzymes. It has been shown to occur in the active sites of chymotrypsin, trypsin, and many other enzymes. The so-called nerve gases and many substances used in insecticides have been shown to act by combining with a residue of serine in the active site of acetylcholine esterase, inhibiting the enzyme completely. The unmetabolized acetylcholine cannot be recycled into the nerve for signaling. This results in depletion of acetylcholine at the neuromuscular junction, resulting in the inability to control muscles, which results in asphyxiation, and death.

As a constituent (residue) of proteins, its side chain can undergo O-linked glycosylation. This might be important in explaining some of the devastating consequences of diabetes. It is one of three amino acid residues that are commonly phosphorylated by kinases during cell signaling in eukaryotes. Phosphorylated serine residues are often referred to as phosphoserine. Serine proteases are a common type of protease.

Signaling

D-serine, synthesized by serine racemase from L-serine, serves as a neuronal signaling molecule by activating NMDA receptors in the brain.. Some evidence suggests that a deficiency in D-serine leads to hypoactivity of NMDA receptors and a resulting psychosis in some cases of schizophrenia. Oral administration of D-serine was therapeutically beneficial in schizophrenia in at least one clinical trial .

Chemical Synthesis

Serine is prepared from methyl acrylate.

See also

• Serine aggregation properties in Serine octamer clusters
• Computational Chemistry Wiki