Atomistic simulation of hydrophobic matching effects on lipid composition near a helical peptide embedded in mixed-lipid bilayers.

The local lipid composition near a transmembrane helical peptide in mixed-lipid bilayers has been studied using a mixed molecular dynamics (MD) and configuration-bias Monte Carlo method that allows the lateral distribution of lipids to equilibrate much more quickly than is possible by diffusive mixing alone. Gramicidin-A peptide was embedded in bilayer mixtures of DMPC with either DDPC (shorter by four carbons per tail) or DSPC (longer by four carbons per tail) at 330 K to investigate the possibility of lipid sorting by tail length. Conventional MD simulations showed local thickening of the bilayer near the peptide in pure DDPC and local thinning of the bilayer in pure DSPC, with comparatively little perturbation to the thickness of pure DMPC bilayers, suggesting that DMPC has the best matched tail length to the peptide of these three. In 1:1 DMPC:DDPC mixtures, the DMPC lipid was weakly enriched (by about 5%) near the peptide, while in DSPC:DMPC mixtures, no consistent trend was observed. The results underscore the weakness of the coupling between membrane deformation and local composition fluctuations in the absence of spontaneous phase separation.