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serine protease reaction mechanism. The main player in the catalytic mechanism in the serine proteases is the catalytic triad. The triad is located in the active site of the enzyme, where catalysis occurs, and is preserved in all superfamilies of serine protease enzymes.
Serine hydrolases are one of the largest known enzyme classes comprising approximately ~200 enzymes or 1% of the genes in the human proteome. [1] A defining characteristic of these enzymes is the presence of a particular serine at the active site , which is used for the hydrolysis of substrates .
The Serine-Histidine-Aspartate motif is one of the most thoroughly characterised catalytic motifs in biochemistry. [3] The triad is exemplified by chymotrypsin, [c] a model serine protease from the PA superfamily which uses its triad to hydrolyse protein backbones.
Acrosin is a typical serine proteinase with trypsin-like specificity. [3]Acrosin catalytic mechanism. The reaction proceeds according to the usual serine protease mechanism. . First, His-57 deprotonates Ser-195, allowing it to serve as a nucleophi
Serine and cysteine proteases operate by a two-step catalytic mechanism. First, the substrate (blue) is attacked by the cysteine or serine of the catalytic triad (red) to form an acyl-enzyme intermediate .
Catalytic triad of a serine protease The initial step of the serine protease catalytic mechanism involves the histidine of the active site accepting a proton from the serine residue. This prepares the serine as a nucleophile to attack the amide bond of the substrate.
It is structurally unrelated to the chymotrypsin-clan of serine proteases, but uses the same type of catalytic triad in the active site. This makes it a classic example of convergent evolution . Mechanism of catalysis
Many enzymes including serine protease, cysteine protease, protein kinase and phosphatase evolved to form transient covalent bonds between them and their substrates to lower the activation energy and allow the reaction to occur. This process can be divided into 2 steps: formation and breakdown.