Mechanism of acid protease catalysis based on the crystal structure of penicillopepsin.

A proposed mechanism for the catalytic hydrolysis of peptide bonds by acid proteases is similar in many respects to the Zn-carbonyl mechanism previously derived for carboxypeptidase A. In the acid proteases the electrophilic component is the proton shared by Asp-32 and Asp-215; Tyr-75 donates its proton to the amide nitrogen of the scissile bond and an OH- ion from a water molecule bound between the carboxyl group of Asp-32 and the substrate attacks the carbonyl carbon atom.