Dipeptidyl peptidase from Streptococcus anginosus with substrate specificity for Xaa-Pro/Ala and potential impact on...

Streptococcus anginosus, an oral commensal bacterium, is a potential risk factor for malignancies of the oral cavity and upper gastrointestinal tract. Although this species harbors an Xaa-Pro dipeptidyl peptidase (DPP), its enzymatic characteristics and potential role in tumor-associated immune modulation remain unclear. In this study, S. anginosus Xaa-Pro DPP was characterized and its ability to cleave chemokine-related peptides was evaluated.

Six oral streptococcal strains were analyzed for DPP activity using fluorogenic dipeptidyl substrates. The gene encoding S. anginosus Xaa-Pro DPP was cloned and the recombinant enzyme was purified and characterized. The enzymatic activity of the peptidase against synthetic dipeptidyl 7-amino-4-methylcoumarin (MCA) and chemokine-derived peptides was assessed using fluorescence assays and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The effect of the DPP4 inhibitor, P32/98, was also examined.

S. anginosus had the highest DPP activity among the tested oral streptococci, particularly towards Gly-Pro- and Lys-Ala-MCA. The recombinant enzyme selectively removed Xaa-Pro and Xaa-Ala dipeptides and the N-terminal Lys-Pro dipeptide from the CXCL12-derived peptide, whereas incretins were minimally affected. The enzymatic activity of Xaa-Pro DPP against synthetic substrates was markedly inhibited by P32/98.

S. anginosus Xaa-Pro DPP has specificity for N-terminal Xaa-Pro/Ala in peptides and exhibits the ability to inactivate chemokine-related peptides, suggesting a potential contribution to immune dysregulation in the tumor microenvironment.