New Insights into Nisin's Antibacterial Mechanism Revealed by Binding Studies with Synthetic Lipid II Analogues

Nisin is the preeminent lantibiotic and to date its antibacterial mechanism has been investigated using a variety of techniques. While nisin's lipid II-mediated mode of action is well established, a detailed analysis of the thermodynamic parameters governing this interaction has not been previously reported. We here describe an approach employing isothermal titration calorimetry to directly measure the affinity of nisin for lipid II and a number of synthetic lipid II precursors and analogues. Our measurements confirm the pyrophosphate unit of lipid II as the primary site of nisin binding and also indicate that the complete MurNAc moiety is required for a high affinity interaction. Additionally, we find that while the pentapeptide unit of the lipid II molecule is not required for strong binding by nisin, it does play an important role in stabilizing the subsequently formed nisin-lipid II pore-complex, albeit at an entropic cost. The anchoring of lipid II in a membrane environment was also found to play a significant role in enhancing nisin binding and is required to achieve a high affinity interaction