Sequence analysis, distribution and expression of an aminopeptidase N-encoding gene from Lactobacillus helveticus CNRZ32.

Lactobacillus (Lb.) helveticus CNRZ32 possesses a 97-kDa metalloenzyme with aminopeptidase activity (PepN; EC 3.4.11.2). A 3.8-kb fragment encoding PepN was cloned into pIL253 and designated pSUW34. Transformation of lactococcus (Lc.) lactis LM0230 with pSUW34 resulted in > 180-fold increase in general aminopeptidase (AP) activity using L-lysine-p-nitroanilide. Southern hybridization was conducted to determine the distribution of homology to the CNRZ32 pepN gene among lactic-acid bacteria (LAB). Hybridization was observed with strains of lactobacilli, pediococci, leuconostoc, streptococci and lactococci. The pepN gene was sequenced and found to encode a protein containing 844 amino acid (aa) residues. A comparison of Lb. helveticus CNRZ32 pepN to Lb. delbrueckii ssp. lactis DSM7290 pepN indicated 69.5% nucleotide (nt) identity and 71.8% aa identity, while comparison to pepN from Lc. lactis ssp. cremoris MG1363 indicated 61.1% nt identity and 49.2% aa identity. Alignment of peptidase aa sequences of LAB, Escherichia coli, yeast and mammalian origin display homology in the zinc-binding domain, as well as a conserved region upstream from the putative active site.