Transition metal ions induce carnosinase activity in PepD-homologous protein from Porphyromonas gingivalis

Aminoacylhistidine dipeptidase (EC 3.4.13.3; also Xaa-His dipeptidase, carnosinase, or PepD) catalyzes the cleavage and release of an N-terminal amino acid, which is usually a neutral or hydrophobic residue, from an Xaa-His dipeptide or degraded peptide fragment. PepD enzyme is found extensively in prokaryotes and eukaryotes, and belongs to the metallopeptidase family M20, a part of the metallopeptidase H (MH) clan. Carnosine is a naturally occurring dipeptide (β-alanyl-l-histidine) present in mammalian tissues that has protective functions in addition to anti-oxidant and free-radical scavenging roles. During bacterial infections, degradation of l-carnosine via carnosinase or PepD-like enzymes may enhance the destructive potential of bacteria, resulting in a pathological impact. This process has been proposed to act in an anti-oxidant manner in vivo. In the present study, the recombinant PepD protein encoded by Porphyromonas gingivalis TDC60 pepD was generated and biochemically characterized. In addition, a recombinant dipeptidase enzyme was found to function not only as an alanine-aminopeptidase, but also as a carnosinase. Furthermore, when carnosine was used as substrate for PepD, the transition metals, Mn²⁺, Fe²⁺, Co²⁺, and Ni²⁺ stimulated the hydrolyzing activity of rPepD with β-alanine and l-histidine. Based on its metal ion specificity, we propose that this enzyme should not only be termed l-aminopeptidase, but also a carnosinase.