Inactivation of cysteine proteases

Area of Science:

• Biochemistry
• Enzymology
• Medicinal Chemistry

Background:

• Cysteine proteases are crucial enzymes involved in various biological processes.
• Understanding their inhibition mechanisms is vital for drug development.
• Peptidyl alpha, beta-unsaturated esters are known inhibitors of cysteine proteases.

Purpose of the Study:

• To investigate the inactivation mechanism of cysteine proteases papain and cathepsin B by a novel Michael acceptor.
• To elucidate the role of stereochemistry (cis vs. trans) of the inhibitor in enzyme inactivation.
• To characterize the binding and inhibition modes of different isomers.

Main Methods:

• Enzyme kinetics assays to determine inhibition constants and inactivation rates.
• Stoichiometric analysis of chloride release during inactivation.
• Comparison of inhibition by trans and cis isomers of the peptidyl-beta-chloro-alpha, beta-unsaturated ester.

Main Results:

• The peptidyl-beta-chloro-alpha, beta-unsaturated ester effectively inactivated papain and cathepsin B.
• Inactivation was stoichiometric with chloride release, suggesting nucleophilic attack by the active site cysteine.
• The trans isomer caused irreversible inactivation, while the cis isomer acted as a competitive inhibitor.
• Steric hindrance from the beta-chlorine substituent likely affects the binding of the cis isomer.

Conclusions:

• The study demonstrates a mechanism-based inactivation of cysteine proteases by a specific Michael acceptor.
• The trans configuration of the inhibitor is essential for effective inactivation.
• Stereochemistry plays a critical role in the inhibitory activity and binding mode of these compounds.