Correlation between Single-Molecule Dynamics and Biological Functions of Antimicrobial Peptide Melittin.

Many fundamental biological processes occur on cell membranes, and a typical example is the membrane permeabilization by peptides for an antimicrobial purpose. Previous studies of the underlying mechanism mostly focus on structural changes of membranes and peptides during their interactions. Herein, from a new perspective of single-molecule dynamics, the real-time three-dimensional motions of individual phospholipid and peptide molecules were monitored, and specifically, their correlation with the membrane poration function of melittin, a most representative natural antimicrobial peptide, was studied. We found that the adsorption and accumulation of melittin on the membrane surface significantly sped up the lateral diffusion of lipids surrounding the peptides, which in turn facilitated the peptide insertion at such heterogeneous regions. A unique "U"-bending pathway of melittin during membrane insertion and the ultimate formation of toroidal pores with dynamical translocations of peptides and lipids with several metastable states between the two leaflets of bilayer were observed.