Summary: subsp. CNRZ 397 () is characterized by a high level of peptidase activities specific to proline-containing peptides. A prolidase (PepQ, EC was purified to homogeneity and characterized as a strict dipeptidase active on X-Pro dipeptides, except Gly-Pro and Pro-Pro. The values for and were, respectively, 2·2 mM and 0·33 mmol min mg, with Leu-Pro as the substrate. The enzyme exhibited optimal activity at 50 °C and pH 6·0, and required the presence of Zn. Size exclusion chromatographies and SDS-PAGE analysis led to the conclusion that this prolidase was a homodimer. Antibodies raised against the purified protein allowed the detection of PepQ among several species but not lactococci. The gene and the upstream region were isolated and sequenced. The deduced peptide sequence showed that PepQ belongs to the M24 family of metallopeptidases. The gene is located immediately upstream of and its product is homologous to the transcription factor CcpA, which is involved in catabolite repression of catabolic operons from Gram-positive bacteria. The intergenic region contains a consensus catabolite-responsive element (CRE) which could be a target for PepR1 protein. Moreover, in contrast to other proline-specific enzymes from PepQ biosynthesis was shown to be dependent on the composition of the culture medium, but not on the peptide concentration. A possible regulation mechanism is discussed.


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