Catalytic properties of the cysteine aminopeptidase PepC, a bacterial bleomycin hydrolase.

PepC is a cytoplasmic thiol aminopeptidase widely conserved among lactic acid bacteria. PepC from Lactococcus lactis shares 35-38% identity with aminopeptidases of eukaryotic origins: the yeast and mammalian bleomycin hydrolases (BLMase). In this work we investigated the hydrolytic activity of PepC towards various substrates: bleomycin A2, aminoacyl-p-nitroanilides (pNA) and peptides. First, we found the bleomycin hydrolase activity of lactococcal PepC and measured similar kinetics parameters to those reported for the mammalian BLMase. Second, the results obtained on aminoacyl-pNA confirmed the capacity of the enzyme to release a broad range of amino acids and the pH activity profile suggests the presence of an ionic interaction between the enzyme and the free alpha-amino group of the substrate. Third, the aminopeptidase activity measured on peptide substrates revealed that PepC possesses an extended binding site which interacts with the peptidic backbone of the substrate. The hydrolytic efficiency is highly dependent on the length of the peptide, optimal for tetrapeptides and further enhanced by the presence of hydrophobic residues in the P' positions of the substrate. These enzymatic properties are of importance for the design of specific inhibitors and the biological function of the bleomycin hydrolases.