Characterization of the Lactococcus lactis pepN gene encoding an aminopeptidase homologous to mammalian aminopeptidase N

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Abstract
The nucleotide sequence of the pepN gene from Lactococcus lactis encoding a zinc‐metallo aminopeptidase has been determined. The open reading frame of 2,538 base pairs encodes a protein with a calculated M r of 95,368, which agrees with the apparent M r of 95,000 of the gene product which was identified by polyclonal antibodies raised against the purified aminopeptidase. The amino acid sequence of the aminopeptidase of L. lactis was found to be similar to the corresponding enzymes of human, rat and mouse, with almost 30% of the residues identical. Also, a highly conserved area was identified which has similarity with the active site of thermolysin. A zinc‐binding site, as well as the catalytic site for PepN, is predicted to lie within this conserved stretch. Putative promoter regions upstream of PepN were confirmed by primer extension analysis.