Studies on chymotrypsin-like catalysis by synthetic peptides

Area of Science:

• Biochemistry
• Enzyme kinetics
• Peptide chemistry

Background:

• The synthetic peptide Chymohelizyme-1 (CHZ-1) was previously reported to have broad catalytic activity.
• Earlier studies suggested CHZ-1 could hydrolyze various esters and amides.

Purpose of the Study:

• To re-evaluate the catalytic activity of Chymohelizyme-1 (CHZ-1).
• To identify the mechanism and substrate specificity of CHZ-1 esterase activity.
• To clarify discrepancies with previous reports on CHZ-1's catalytic function.

Main Methods:

• Enzyme activity assays using specific ester substrates like carbobenzoxytyrosine p-nitrophenyl ester (ZTONP), carbobenzoxyalanine p-nitrophenyl ester (ZAONP), and t-butyloxy-carbonyltyrosine p-nitrophenyl ester (BocTONP).
• pH dependence studies to elucidate the catalytic mechanism.
• Analysis of substrate preference to understand structure-activity relationships.

Main Results:

• CHZ-1 exhibits esterase activity against ZTONP, ZAONP, and BocTONP.
• Previous reports of activity against less labile esters and amides were found to be incorrect, attributed to omitted controls.
• Catalytic triad does not function as designed, but activity depends on primary structure integrity.
• pH dependence suggests general-base catalysis for ZTONP hydrolysis.
• Preference for hydrophobic substrates indicates a structural role in catalysis.

Conclusions:

• CHZ-1 possesses specific esterase activity, correcting prior overestimations of its catalytic scope.
• The peptide's catalytic mechanism is not a typical triad-based serine protease mechanism.
• CHZ-1's structure plays a crucial role in its observed esterase activity, potentially through general-base catalysis and hydrophobic interactions.