ROLE OF LIPID-BOUND PEPTIDOGLYCAN PRECURSORS IN THE FORMATION OF PORES BY NISIN, EPIDERMIN AND OTHER LANTIBIOTICS

It is generally assumed that type A lantibiotics primarily kill bacter ia by permeabilization of the cytoplasmic membrane, As previous studie s had demonstrated that nisin interacts with the membrane-bound peptid oglycan precursors lipid I and lipid II, we presumed that this interac tion could play a role in the pore formation process of lantibiotics. Using a thin-layer chromatography system, we found that only nisin and epidermin, but not Pep5, can form a complex with [C-14]-lipid II. Lip id II was then purified from Micrococcus luteus and incorporated into carboxyfluorescein-loaded liposomes made of phosphatidylcholine and ch olesterol (1:1). Liposomes supplemented with 0.05 or 0.1 mol% of lipid II did not release any marker when treated with Pep5 or epilancin K7 (peptide concentrations of up to 5 mol% were tested). In contrast, as little as 0.01 mol% of epidermin and 0.1 mol% of nisin were sufficient to induce rapid marker release; phosphatidylglycerol-containing lipos omes were even more susceptible. Controls with moenomycin-, undecapren ol- or dodecaprenolphosphate-doped liposomes demonstrated the specific ity of the lantibiotics for lipid II. These results were correlated wi th intact cells in an in vivo model, M. luteus and Staphylococcus simu lans were depleted of lipid II by preincubation with the lipopeptide r amoplanin and then tested for pore formation. When applied in concentr ations below the minimal inhibitory concentration (MIC) and up to 5-10 times the MIC, the pore formation by nisin and epidermin was blocked; at higher concentrations of the lantibiotics the protective effect of ramoplanin disappeared. These results demonstrate that, in vitro and in vivo, lipid II serves as a docking molecule for nisin and epidermin , but not for Pep5 and epilancin K7, and thereby facilitates the forma tion of pores in the cytoplasmic membrane.