Enterococcus faecalis cytolysin and lactocin S of Lactobacillus sake

Abstract

Strains of Enterococcus faecalis and Lactobacillus sake have been found to express lantibiotics with unusual properties. The enterococcal lantibiotic is unusual in that it consists of two dissimilar subunits, both putatively containing modifications consistent with those found in other lantibiotics. The enterococal lantibiotic is also unusual in the number of proteolytic steps involved in secretion signal removal and activation. Moreover, it has been observed to contribute to enterococcal disease in humans and in animal models. Structrural studies of lactocin S, expressed by a strain of L. sake highlight unique properties including the presence of D-alanine within its structure, and a protease putatively responsible for lactocin S secretion signal peptide removal which, itself, lacks a signal or propeptide sequence. Despite the unusual properties of each of these lantibiotics, the operons encoding each, and accompanying auxiliary functions, are collinear suggeting a common ancestry. The accretion of interdigitating DNA sequences between genes encoded within the lactocin S determinant are unique to that determinant, however, and are of unknown function.