BIOCHEMICAL AND GENETIC-CHARACTERIZATION OF ENTEROCIN-A FROM ENTEROCOCCUS-FAECIUM, A NEW ANTILISTERIAL BACTERIOCIN IN THE PEDIOCIN FAMILY OF BACTERIOCINS

A new bacteriocin has been isolated from an Enterococcus faecium strai n. The bacteriocin, termed enterocin A, was purified to homogeneity as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, N-terminal amino acid sequencing, and mass spectrometry analysis. By c ombining the data obtained from amino acid and DNA sequencing, the pri mary structure of enterocin A was determined. It consists of 47 amino acid residues, and the molecular weight was calculated to be 4,829, as suming that the four cysteine residues form intramolecular disulfide b ridges. This molecular weight was confirmed by mass spectrometry analy sis. The amino acid sequence of enterocin A shared significant homolog y with a group of bacteriocins (now termed pediocin-like bacteriocins) isolated from a variety of lactic acid-producing bacteria, which incl ude members of the genera Lactobacillus, Pediococcus, Leuconostoc, and Carnobacterium. Sequencing of the structural gene of enterocin A,whic h is located on the bacterial chromosome, revealed an N-terminal leade r sequence of 18 amino acid residues, which was removed during the mat uration process. The enterocin A leader belongs to the double-glycine leaders which are found among most other small nonlantibiotic bacterio cins, some lantibiotics, and colicin V. Downstream of the enterocin A gene was located a second open reading frame, encoding a putative prot ein of 103 amino acid residues. This gene may encode the immunity fact or of enterocin A, and it shares 40% identity with a similar open read ing frame in the operon of leucocin AUL 187, another pediocin-like bac teriocin.