Saccharomyces cerevisiae KEX1 gene product
Structure of wheat serine carboxypeptidase II at 3.5-A resolution. A new class of serine proteinase.
Refined atomic model of wheat serine carboxypeptidase II at 2.2-A resolution.
Structure of the complex of L-benzylsuccinate with wheat serine carboxypeptidase II at 2.0-A resolution.
X-ray crystallography (2.1/2.5 Angstroms)
Peptide aldehyde complexes with wheat serine carboxypeptidase II: implications for the catalytic mechanism and substrate specificity.
This enzyme belongs to the peptidase family-S10. According to the literature [2], [3] & [4], this enzyme has got a catalytic triad, Ser146/His397/Asp338, and an oxyainon hole, made of the backbone amides of Tyr147 and Gly53. Thus, this enzyme also performs two-step reaction, acylation and deacylation, like other serine hydrolases. Ser146 acts as a nucleophile to attack on the carbonyl carbon atom to form an acyl-enzyme intermediate in the acylation process. Meanwhile, an Asp-His pair acts to deprotonate the hydroxyl of the catalytic serine to make it nucleophilic. In this pair of residues, a strong electrostatic interaction between the sidechains stabilizes the imidazolium cation developed during the catalysis, according to the paper [2]. Although the catalytic mechanism of this enzyme is very similar to those of other serine hydrolases, it has several distinct features (see [3] & [4]). Firstly, according to the paper [3], a C-terminal carboxylate of the substrate might atc as a proton sink for the catalytic His397. Here, in an acid-base preequilibrium, transfer of a proton from the protonated histidine to the substrate carboxylate neutralizes both the residue itself and the substrate, and then the conventional mechanism of serine hydrolases can proceed [3]. For this preequilibrium, the interaction of Glu145 with the substrate carboxylate might play an important role in the transition state [3]. Secondly, the stereochemistry of an enzymatic reaction seems to be opposite to that of other serine hydrolases, such as proteinase A (see [4]). This dissimilarity can distinguish these enzymes which have such a catalytic triad, Ser/His/Asp, in terms of evolution [4].