Cloning and nucleotide sequence analysis of pepV, a carnosinase gene from Lactobacillus delbrueckii subsp. lactis DSM 7290, and partial characterization of the enzyme

摘要

Cell extracts of Lactobacillus delbrueckii subsp. lactis DSM 7290 were found to exhibit unique peptolytic ability against unusual β-alanyl-dipeptides. In order to clone the gene encoding this activity, designated pepV, a gene library of strain DSM 7290 genomic DNA, prepared in the low-copy-number plasmid pLG339, was screened for heterologous expression in Escherichia coli. Recombinant clones harbouring pepV were identified by their ability to allow the utilization of carnosine (β-alanyl-histidine) as a source of histidine by the E. coli mutant strain UK197 (pepD, hisG). Complementation was observed in a colony harbouring a recombinant plasmid (pKV101), carrying pepV. A 2.4 kb fragment containing pepV was subcloned and its nucleotide sequence revealed an open reading frame (ORF) of 1413 nucleotides, corresponding to a protein with predicted molecular mass of 51998 Da. A single transcription initiation site 71 bp upstream of the ATG translational start codon was identified by primer extension. No significant homology was detected between pepV or its deduced amino acid sequence with any entry in the databases. The only similarity was found in a region conserved in the ArgE/DapE/CPG2/YscS family of proteins. This observation, and protease inhibitor studies, indicated that pepV is of the metalloprotease type. A second ORF present in the sequenced fragment showed extensive homology to a variety of amino acid permeases from E. coli and Saccharomyces cerevisiae.