Design of protease inhibitors on the basis of substrate stereospecificity

✍ Scribed by Dong H. Kim

• Publisher: Wiley (John Wiley & Sons)
• Year: 1999
• Tongue: English
• Weight: 77 KB
• Volume: 51
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/(sici)1097-0282(1999)51:1<3::aid-bip2>3.0.co;2-q

✦ Synopsis

The substrate stereospecificity in enzymic reactions, which is one of characteristics of enzymes along with the substrate and regiospecificity can provide a basis for the rational design of inhibitors. This has been demonstrated using ␣-chymotrypsin, a prototypic serine protease as a model enzyme. On the basis of the structure-activity relationships for substrates as well as inhibitors and mechanism of the enzymic reaction, a schematic three-dimensional model of the S 1 subsite of ␣-chymotrypsin is constructed. It was envisioned from the three-dimensional active site model that 2-benzyl-3,4-epoxybutanoic acid methyl ester (1) having a (2S)-configuration would bind the enzyme with its oxirane ring being rested at the catalytic site, in which the oxirane ring is subject to a nucleophilic attack by the Ser-195 hydroxyl to form a ether linkage. Kinetic analysis of the enzymic reaction in the presence of the potential inhibitors showed that (2S,3R)-1 inactivates ␣-chymotrypsin, while (2S,3S)-1 inhibits the enzyme competitively. The lack of inactivating activity in the case of (2S,3S)-1 may be due to the unfavorable alignment of the C 3 -O bond with respect to the hydroxyl of Ser-195 for the S N 2-type ring cleave reaction of the oxirane moiety. When the design protocol was applied to papain, a representative cysteine protease, (2S,3S)-1 inhibited the enzyme irreversibly, while (2S,3R)-1 inhibited reversibly. On the basis of the stereospecificity shown in the inactivation of the enzymes, it was inferred that in the case of ␣-chymotrypsin, the nucleophilic attack of the Ser-195 hydroxyl at the scissile carbonyl carbon of substrates occurs in a si fashion, while the thiolate of Cys-25 in papain attacks the substrate amide bond in a re fashion. The inhibitor design protocol may be applied to other proteases.