Peptide-Induced Lipid Flip-Flop in Asymmetric Liposomes Measured by Small Angle Neutron Scattering

摘要: Despite the prevalence of lipid transbilayer asymmetry in natural plasma membranes, most biomimetic model membranes studied are symmetric. Recent advances have helped to overcome difficulties preparing asymmetric liposomes vitro, allowing for examination a larger set relevant biophysical questions. Here, we investigate stability bilayers by measuring flip-flop with time-resolved small-angle neutron scattering (SANS). Asymmetric large unilamellar vesicles inner bilayer leaflets containing predominantly 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and outer composed mainly 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) displayed slow spontaneous at 37 ◦C (half-time, t1/2 = 140 h). However, inclusion peptides, namely, gramicidin, alamethicin, melittin, or pHLIP (i.e., pH-low insertion peptide), accelerated flip-flop. For three these peptides pHLIP, melittin), each which was added externally preformed vesicles, observed completely scrambled less than 2 h. Gramicidin, on other hand, preincorporated during formation showed time resolvable 8-fold increase rate loss. These results point membrane surface-related (e.g., adsorption/insertion) event as primary driver scrambling this study. We discuss implications peptide binding, conformation, asymmetry.