Concentration-Dependent Modes of Melittin-Induced Membrane Destabilization: An Integration of Experimental and Computational Tools.

Melittin is a well-known antimicrobial peptide whose mechanism of action is still not entirely understood. In this study, we combine complementary experimental techniques with molecular dynamics simulations to determine melittin-membrane interactions at different scales. Using 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE): 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG) membranes that mimic the Escherichia coli inner membrane, this integrative approach reveals a clear transition in melittin's mode of action with increasing peptide loading. At low concentrations, melittin primarily perturbs the membrane interface, inducing modest surface expansion and subtle lipid reorganization. At higher concentrations, the membrane response shifts toward increased hydration, lipid disorder, membrane thinning, and morphological remodeling. Simulations support these observations, linking concentration-dependent membrane responses to enhanced lipid mobility and stronger effects on anionic DPPG. Melittin, therefore, affects the membrane in a concentration-dependent manner, transitioning from surface-bound carpet-like permeabilization at low loading to transient pore formation and membrane reorganization at higher concentrations.