CLONING AND SEQUENCE-ANALYSIS OF THE X-PROLYL-DIPEPTIDYL-AMINOPEPTIDASE GENE (PEPX) FROM LACTOBACILLUS-DELBRUCKII SSP LACTIS DSM7290

Lactobacillus delbruckii ssp. lactis DSM7290 possesses an X-prolyl-dip eptidyl-aminopeptidase, designated PepX, which catalyses the hydrolyti c removal of N-terminal dipeptidyl residues from peptides containing p roline in the penultimate position. Using the specific substrate L-Ala -L-Pro-p-nitroanilide, PepX was purified by a four-step procedure incl uding ammonium sulphate fractionation, hydrophobic interaction chromat ography, ion exchange chromatography, and affinity chromatography. The N-terminus of the purified protein was sequenced. Screening of a gene library of chromosomal Lactobacillus delbruckii ssp. lactis DSM7290 D NA in the low-copy-number vector pLG339 resulted in the identification of the pepX gene in Escherichia coli using a specific plate assay wit h Gly-L-Pro-beta-naphthylamide as substrate. Nucleotide sequence analy sis revealed an open reading frame of 2376 bp, coding for a protein of 792 amino acids with a molecular mass of 88449 Da.