Heterodimer and pore formation of magainin 2 and PGLa: The anchoring and tilting of peptides in lipid bilayers

Mixtures of Magainin 2 and PGLa are simulated with 94 nm-sized bilayers composed of phospholipids and lysophospholipids for 3 mu s using coarse-grained force fields. Calculation of the bilayer bending modulus shows that bilayers become more flexible in the presence of lyso-lipids or peptides, in agreement with experiments. Starting with the initial configuration of peptides randomly distributed on the bilayer surface, peptides aggregate, insert to the bilayer, and form pores. Aggregated peptides do not retain side-by-side heterodimeric structure but instead show the anchoring between C-terminal groups of magainin 2 and PGLa, which allows the deeper insertion of PGLa into the bilayer. In particular, due to the anchoring of magainin 2 and PGLa, the deeply inserted PGLa pull magainin 2 into contact with the edge of the opposite leaflet of the bilayer, which stabilizes the pore. In addition to these biophysical insights, anionic unsaturated-phospholipid bilayers are also simulated to mimic bacterial cell membranes, showing less extent of PGLa insertion and no pore formation. These simulation findings indicate that these synergistic heterodimers have the anchoring structure rather than the side-by-side structure, which supports the experimental observations suggesting the deeper insertion of PGLa and pore formation via the anchoring between anionic C-terminus of magainin 2 and cationic C-terminus of PGLa.