Cloning and nucleotide sequence analysis of pepV, a carnosinase gene from Lactobacillus delbrueckiisubsp. lactisDSM 7290, and partial characterization of the enzyme
Cell extracts of Lactobacillus delbrueckiisubsp. lactisDSM 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 pepVwere identified by their ability to allow the utilization of carnosine (β-alanyl-histidine) as a source of histidine by the E. colimutant strain UK197 (pepD, hisG). Complementation was observed in a colony harbouring a recombinant plasmid (pKV101), carrying pepV.A 2.4 kb fragment containing pepVwas 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 pepVor 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 pepVis of the metalloprotease type. A second ORF present in the sequenced fragment showed extensive homology to a variety of amino acid permeases from E. coliand Saccharomyces cerevisiae.
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Cloning and nucleotide sequence analysis of pepV, a carnosinase gene from Lactobacillus delbrueckiisubsp. lactisDSM 7290, and partial characterization of the enzyme