Assembly and stability of nisin-lipid II pores.

The peptide antibiotic nisin was the first reported example of an antibiotic that kills bacteria via targeted pore formation. The specific target of nisin is Lipid II, an essential intermediate in the bacterial cell-wall synthesis. High-affinity binding of the antibiotic to Lipid II is followed by rapid permeabilization of the membrane. Here, we investigated the assembly and stability of nisin-Lipid II pore complexes by means of pyrene fluorescence and circular dichroism. We demonstrated that nisin uses all available Lipid II molecules in the membrane to form pore complexes. The pore complexes have a uniform structure and consist of 8 nisin and 4 Lipid II molecules. Moreover, the pores displayed a remarkable stability, because they were able to resist the solubilization of the membrane environment by mild detergents. Similar experiments with [N20P/M21P]nisin showed that the hinge region is essential for the assembly into stable pore complexes. The new insights were used to propose a refined model for nisin pore formation.