Glycine flanked by hydrophobic bulky amino acid residues as minimal sequence for effective subtilisin catalysis

The specificity of alkaline mesentericopeptidase (a proteinase closely related to subtilisin BPN9) for the C-terminal moiety of the peptide substrate (Pi9 specificity) has been studied in both hydrolysis and aminolysis reactions. N-Anthraniloylated peptide p-nitroanilides as fluorogenic substrates and amino acid or peptide derivatives as nucleophiles were used in the enzymic peptide hydrolysis and synthesis. Both hydrolysis and aminolysis kinetic data suggest a stringent specificity of mesentericopeptidase and related subtilisins to glycine as P1′ residue and predilection for bulky hydrophobic P2′ residues. A synergism in the action of S1′ and S2′subsites has been observed. It appears that glycine flanked on both sides by hydrophobic bulky amino acid residues is the minimal amino acid sequence for an effective subtilisin catalysis.