THE C-TERMINAL REGION OF NISIN IS RESPONSIBLE FOR THE INITIAL INTERACTION OF NISIN WITH THE TARGET MEMBRANE

The interaction of nisin Z and a nisin Z mutant carrying a negative ch arge in the C-terminus ([Glu-32]-nisin Z) with anionic lipids was char acterized in model membrane systems, and bacterial membrane systems. W e focused on three possible steps in the mode of action of nisin, i.e. , binding, insertion, and pore formation of nisin Z. Increasing amount s of anionic lipids in both model and natural membranes were found to strongly enhance the interaction of nisin Z with the membranes at all stages. The results reveal a good correlation between the anionic lipi d dependency of the three stages of interaction, of which the increase d binding is probably the major determinant for antimicrobial activity . Maximal nisin Z activity could be observed for negatively charged li pid concentrations exceeding 50-60%, both in model membrane systems as well as in bacterial membrane systems. We propose that the amount of negatively charged lipids of the bacterial target membrane is a major determinant for the sensitivity of the organism for nisin. Nisin Z ind uced leakage of the anionic carboxyfluorescein was more efficient as c ompared to the leakage of the potassium cation. This lead to the concl usion that an anion-selective pore is formed. In contrast to the resul ts obtained for nisin Z, the binding of [Glu-32]-nisin Z to vesicles r emained low even in the presence of high amounts of negatively charged lipids. The insertion and pore-forming ability of [Glu-32]-nisin Z we re also decreased. These results demonstrate that the C-terminus of ni sin is responsible for the initial interaction of nisin, i.e., binding to the target membrane.