Molecular dynamics and H-2-NMR study of the influence of an amphiphilic peptide on membrane order and dynamics

A molecular dynamics simulation of a fully hydrated model membrane consisti ng of 12 molecules of 1,2-dimyristoyl-sn-glycero-3-phosphocholine, one amph iphilic peptide with the sequence acetyl-Lys-Lys-Gly-Leu(16)-Lys-Lys-Ala-am ide, and 593 water molecules was performed for 1.06 ns (Belohorcova, K., J. H. Davis, T.B. Woolf, and B. Roux. 1997. Biophys. J. 73:3039-3055). The ana lysis presented here is primarily focused on the phospholipid component and the results are compared with experimental H-2-NMR studies of the lipid co mponent of mixtures of the same peptide and lipid at a molar ratio of 1:32, and with earlier studies of closely related peptide/lipid mixtures. The ph ospholipid chain and headgroup isomer populations and isomerization rates c ompare favorably with previous simulations and experimental measurements. O f particular interest is the effect of the peptide on the phospholipid head group and hydrocarbon chain orientational order calculated from the simulat ion, which also agree well with experimental measurements performed on this and closely related systems. Comparison of the experimental results with t he simulations not only shows that there is significant agreement between t he two methods, but also provides new insight into the effect of the peptid e on the lipid dynamics. In particular, these results confirm that a membra ne spanning peptide has little effect on lipid chain order, and bilayer thi ckness if its hydrophobic length closely matches the lipid hydrocarbon thic kness. In addition, we find that the peptide can have a strong ordering eff ect if it is longer than the lipid hydrophobic thickness.