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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.
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
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.
Oxyanion hole of a serine protease (black) stabilises negative charge build-up on the transition state of the substrate (red) using hydrogen bonds from enzyme's backbone amides (blue). An oxyanion hole is a pocket in the active site of an enzyme that stabilizes transition state negative charge on a deprotonated oxygen or alkoxide. [1]
These enzymes differ from serine proteases in that they use a nucleophilic cysteine residue, rather than a serine, in their active site. [42] Nonetheless, the enzymatic chemistry is similar, and the mechanism of inhibition by serpins is the same for both classes of protease. [ 43 ]
The catalytic serine residue in the protease target attacks the stressed conformation of the RSL loop to form an acyl intermediate. The loop then undergoes a conformational change to the relaxed state irreversibly trapping the protease in an inactive state. Hence the serpin functions as a suicide inhibitor of the protease. [11]
In vivo, chymotrypsin is a proteolytic enzyme (serine protease) acting in the digestive systems of many organisms. It facilitates the cleavage of peptide bonds by a hydrolysis reaction, which despite being thermodynamically favorable, occurs extremely slowly in the absence of a catalyst. The main substrates of chymotrypsin are peptide bonds in ...
Transmembrane protease, serine 2 is an enzyme that in humans is encoded by the TMPRSS2 gene. [ 5 ] [ 6 ] [ 7 ] It belongs to the TMPRSS family of proteins, whose members are transmembrane proteins which have a serine protease activity. [ 8 ]