Cysteine protease inhibition by azapeptide esters

Area of Science:

• Biochemistry
• Enzymology
• Medicinal Chemistry

Background:

• Papain is a well-characterized cysteine protease.
• Cysteine proteases play crucial roles in various biological processes.
• Developing selective inhibitors for cysteine proteases is of therapeutic interest.

Purpose of the Study:

• To design and synthesize novel azapeptide esters as potential inhibitors of papain.
• To investigate the mechanism and kinetics of papain inhibition by these novel compounds.
• To assess the selectivity of these inhibitors towards cysteine proteases over serine proteases.

Main Methods:

• Synthesis of azapeptide esters containing an azaglycine moiety.
• Enzyme inhibition assays to determine inhibition rates (k_inact/K_i).
• Time-dependent inhibition studies.
• Enzyme reactivation experiments.
• Selectivity assays against serine proteases.

Main Results:

• Azapeptide esters demonstrated time-dependent inhibition of papain.
• Inhibition rates varied significantly based on the ester group (e.g., >11,000 M-1s-1 for Ac-L-PheAglyOPh).
• Inhibition was substrate-dependent and irreversible upon dialysis.
• Reactivation was achieved with valine methyl ester, suggesting active-site thiol acylation.
• Azaalanine-based peptides showed slower inhibition.
• Azapeptide alkyl esters were unreactive towards serine proteases, indicating selectivity.

Conclusions:

• Azapeptide esters are potent and selective inhibitors of cysteine proteases, exemplified by papain.
• The mechanism involves time-dependent acylation of the active-site thiol.
• These findings support the development of azapeptide esters as targeted therapeutic agents for diseases involving cysteine proteases.