Cloning and nucleotide sequence analysis of the Lactobacillus delbrueckii ssp. lactis DSM7290 cysteine aminopeptidase gene pepC.

A genomic library of Lactobacillus delbrueckii ssp. lactis DSM7290 in the low copy number vector pLG339, was screened for the presence of peptidase genes. Using the chromogenic substrate gly-ala-beta-naphthylamide, which is not a substrate for any of the recently cloned peptidases of DSM7290, and the multiple peptidase deficient Escherichia coli strain CM89, allowed the isolation of clones, which contained the equivalent hydrolytic activity. To identify genes encoding the conserved catalytic active site of cysteine proteases, partial nucleotide sequencing with a degenerate oligonucleotide was performed on recombinant plasmids isolated from such clones. This allowed to identify two out of nine clones to carry the Lactobacillus pepC gene. A total of 2026 nucleotides were determined, and sequence analysis revealed a gene with strong homology to the recently cloned Lb. helveticus (73.2%) and Lactococcus lactis (51.03%) pepC genes, and the derived protein showed homology with the active site of a large number of cysteine proteases. The predicted open reading frame consists of 449 codons, coding for a protein of 50,909 Da. The enzyme is functional and extremely overexpressed in E. coli.