Biochemical and genetic characterization of PepF, an oligopeptidase from Lactococcus lactis

Lactococcus lactis possesses a complex proteolytic system which is essential for its growth in milk. We characterized one of the peptidases of this system, oligopeptidase PepF, together with its structural gene. PepF hydrolyzed peptides containing between 7 and 17 amino acids with a rather wide specificity. It was purified to homogeneity. The N-terminal sequences of PepF and of peptides resulting from tryptic digestion of PepF were determined and used to design degenerate oligonucleotides which served to amplify a DNA fragment internal to pepF. This fragment was used as a probe to screen a lactococcal genomic library in Escherichia coli and to clone the entire gene pepF. The gene coded for a 70 kDa protein and was located on a 55-kilobase lactose-protease plasmid. A motif His-Glu-X-X-His, characteristic of metallopeptidases was evidenced. Two regions of PepF were found similar, first to a stretch of 43 amino acids around the zinc-binding site of several other peptidases, second to a stretch of 33 amino acids well conserved among creatine and arginine kinases. Preliminary results suggest the presence of a second copy of pepF.