Phospholipid flip-flop modulated by transmembrane peptides WALP and melittin

Abstract

Select transmembrane proteins found in biogenic membranes are known to facilitate rapid bidirectional flip-flop of lipids between the membrane leaflets, while others have no little or no effect. The particular characteristics which determine the extent to which a protein will facilitate flip-flop are still unknown. To determine if the relative polarity of the transmembrane protein segment influences its capacity for facilitation of flip-flop, we have studied lipid flip-flop dynamics for bilayers containing the peptides WALP 23 and melittin. WALP 23 is used as a model hydrophobic peptide, while melittin consists of both hydrophobic and hydrophilic residues. Sum-frequency vibrational spectroscopy (SFVS) was used to characterize the bilayers and determine the kinetics of flip-flop for the lipid component, 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), within the mixed bilayers. The kinetics data were utilized to determine the activation thermodynamics for DSPC flip-flop in the presence of the peptides. Melittin was found to significantly reduce the free energy barrier to DSPC flip-flop when incorporated into the bilayer at 1 mol%, while incorporation of WALP 23 at the same concentration led to a more modest reduction of the free energy barrier. The possible mechanisms by which these peptides facilitate flip-flop are analyzed and discussed in terms of the observed activation thermodynamics.

Multistep Molecular Dynamics Simulations Identify the Highly Cooperative Activity of Melittin in Recognizing and Stabilizing Membrane Pores

“…It is worth noting in this context, that a number of experimental studies have concluded that antimicrobial peptide adsorption can induce more rapid lipid flip-flop rates in the bilayers. Fattal et al 47 and Matsuzaki et al 48 attributed the increased rate to a peptide-induced membrane pore, whereas Anglin et al 49 suggest instead that melittin facilitates Figure 2A shows that this (small) pore first appears when the lipid head is constrained to lie 0.4 nm away from the bilayer centre. Figure 2B shows a sequence of snapshots from the sampled umbrella window at this lipid distance.…”

Current Understanding of the Mechanisms by which Membrane-Active Peptides Permeate and Disrupt Model Lipid Membranes

“…We note that melittin has also been reported to enhance lipid flip-flop rates [98]. However, a thermodynamic study by Anglin et al indicates that melittin facilitates lipid flip-flop by thinning the lipid bilayer, rather than by generating membrane pores [98].…”

Antimicrobial peptide dendrimer interacts with phosphocholine membranes in a fluidity dependent manner: A neutron reflection study combined with molecular dynamics simulations

“…A large fraction of the lipids in the upper monolayer were clearly displaced by the dendrimer and transferred to the proximal leaflet until full surface coverage was reached (100%). Flip-flop of lipids in a gel-phase membrane is typically extremely slow with a half-life of several hours, but it is speeded up by defects [49] as well as by membrane-penetrating molecules such as peptides [50,51]. Therefore, it is not surprising that flip-flop of gel-phase DPPC was observed in the incomplete supported bilayer upon dendrimer penetration.…”