Peptidases acyl transfer

Clearly, the oxyanion hole is now as significant a feature of the binding site of such acyl transfer abzymes as it is already for esterases and peptidases — and not without good reason. Knossow has analysed the structures of three esterase-like catalytic antibodies, each elicited in response to the same phosphonate TSA hapten (Charbonnier et al., 1997). Catalysis for all three is accounted for by transition state stabilization and in each case there is an... 

One particularly interesting area which has not been subjected to detailed study is metal-promoted acyl transfer. Studies on esterases and peptidases have shown that acyl transfer occurs to a nucleophilic group of the enzyme within an enzyme-substrate complex and the acyl group is then hydrolyzed in the second step. Many of these enzymes, e.g. carboxypeptidase, contain zinc(II). 

An understanding of the molecular interactions between the acylenzyme and the attacking nucleophilic amine component allows an optimization of the acyl transfer efficiency. The efficiency of the nucleophilic attack of the amine component depends essentially on an optimal binding within the active site by S - P interactions (Fig. 12.5-11). Consequently, more information on the specificity of the S subsites of serine and cysteine peptidases are useful, which can be obtained by systematic acyl transfer studies using libraries of nucleophilic amine components. According to the definition of the p value (see above) small values of p indicate high S subsite specificity for the appropriate amine component in peptidase-catalyzed acyl transfer reactions. 

Figure 72.5-77. Schematic representation of subsite-substrate interactions in the course of the acyl transfer from the acylenzyme to the nucleophilic amine component catalyzed by a serine peptidase.

Gln-Gln-Phe-Gly9-OMe was formed by chymotrypsin-catalyzed transpeptidation in the presence of H-Phe-GIy-OMe. In a papain-catalyzed acyl transfer reaction and subsequent tryptic cleavage, the resulting dodecapeptide ester was converted into substance P. These results indicate that peptides can be readily produced by a combination of recombinant DNA technology and peptidase-catalyzed conversion with the advantage of possible incorporation of groups other than coded amino acids into the recombinant product. 

Acyl transfer processes are of immense strategic and synthetic importance in synthesis and biology. In Fignre 12, the ability of peptidases snch as chymotrypsin to cleave amide bonds using a nncleophilic serine-195 residne to generate an activated acyl-enzyme intermediate was described. Numerous supramolecular structures have been designed that mimic these natural enzymatic acyl transfer processes, such as Lehn s crown ether/ammonium ion complexation... 

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