Amino acid residues essential for catalysis by peptidyl dipeptidase-4 from Pseudomonas maltophilia

Area of Science:

• Biochemistry
• Enzymology
• Protein Chemistry

Background:

• Prokaryotic peptidyl dipeptidase-4 (PDP) is an enzyme with a critical role in biological processes.
• Understanding the enzyme's catalytic mechanism requires identifying key amino acid residues involved in its active site.

Purpose of the Study:

• To investigate the essential residues responsible for the catalytic activity of prokaryotic peptidyl dipeptidase-4.
• To determine the location of these essential residues within the enzyme's catalytic site.

Main Methods:

• Chemical modification of the enzyme using various reagents (tetranitromethane, N-acetylimidazole, trinitrobenzenesulfonic acid, diethyl pyrocarbonate).
• Assessing enzyme activity loss after chemical modification.
• Reversal of inactivation using hydroxylamine.
• Protection assays using a competitive inhibitor (Phe-Arg) and a substrate (Hip-Phe-Arg).

Main Results:

• Tetranitromethane and N-acetylimidazole inactivated the enzyme, with N-acetylimidazole's effect reversed by hydroxylamine, indicating an essential tyrosine residue.
• Trinitrobenzenesulfonic acid and diethyl pyrocarbonate also quenched activity, suggesting an essential lysine residue, as inactivation was not reversed by hydroxylamine.
• The competitive inhibitor protected against inactivation by tetranitromethane and N-acetylimidazole, while the substrate protected against inactivation by trinitrobenzenesulfonic acid and diethyl pyrocarbonate.

Conclusions:

• Both tyrosine and lysine residues are essential for the catalytic activity of prokaryotic peptidyl dipeptidase-4.
• These identified residues are located at the enzyme's catalytic site, as evidenced by protection studies.