Phospholipid Ether Linkages Significantly Modulate the Membrane Affinity of the Antimicrobial Peptide Novicidin

The biological activity of antimicrobial peptides is believed to be closely linked to their ability to perturb bacterial membranes. This makes it important to understand the basis of their membrane-binding properties. Here, we present a biophysical analysis of the interactions of the antimicrobial peptide Novicidin (Nc) with ether- and ester-linked C14 phospholipid vesicles below and above the lipid phase transition temperature (t p). These interactions are strongly dependent on whether the lipids contain ether or ester linkages. Nc is in random coil state in solution but undergoes a large increase in α-helicity in ether vesicles, and to a much smaller extent in ester vesicles, around the t p. This structure is lost at higher temperatures. Steady-state fluorescence and stopped-flow kinetics using fluorophore-labeled Nc reveal that Nc binds more strongly to ether vesicles than to ester vesicles below the t p, while there is no significant difference above the t p. This may reflect ether lipid interdigitation in the gel phase. Isothermal titration calorimetry reveals that partitioning of Nc into both lipids is exothermic and thus enthalpy driven. The higher enthalpy associated with binding to ether lipid may be linked to Nc's higher propensity to form α-helical structure in this lipid. The large effect of the ether-ester interchange reveals that membrane-AMP interactions can be strongly modulated by charge-neutral head group changes.