STRUCTURAL-ANALYSIS AND PROTEOLYTIC ACTIVATION OF ENTEROCOCCUS-FAECALIS CYTOLYSIN, A NOVEL LANTIBIOTIC

Clinical isolates of Enterococcus faecalis more commonly produce a cyt olysin than do commensal isolates. Epidemiologic evidence and animal-m odel studies have established a role for the cytolysin in the pathogen esis of enterococcal disease. The cytolysin consists of two structural subunits, CylL(L) and CylL(S), that are activated by a third componen t, CylA. Genetic and biochemical characterization of CylA indicate tha t it is a serine protease, and that activation putatively results from cleavage of one or both cytolysin subunits. Genetic evidence also sug gests that the cytolysin subunits are related to the rapidly growing c lass of bacteriocins termed lantibiotics. However, unlike lantibiotics , the cytolysin is lytic for eukaryotic as well as prokaryotic cells, and it consists of two structural subunits. This report describes the purification and characterization of the cytolysin subunits and detect ion of lanthionine-type post-translational modifications within their structures. Furthermore, the cleavage specificity of the CylA activato r is reported and it is shown that proteolytic activation of both subu nits is essential for activity.