Dyck Martina, Krüger Peter, Lösche Mathias
Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.
Phys Chem Chem Phys. 2005 Jan 7;7(1):150-6. doi: 10.1039/b410863a.
Subtle differences in the molecular conformation of fully hydrated phospholipids, and in their interaction with the water reservoir, were assessed as functions of headgroup methylation with surface-sensitive X-ray scattering. To achieve such a structural and functional comparison, diacylphosphatidylethanolamines (PEs) and their mono-, di- and trimethylated (diacylphosphatidylcholine, PC) derivatives in surface monolayers on water have been studied. While the molecular structures of these lipids are quite similar, their subtle distinctions lead to surprisingly large differences in their overall organization. Independent of the surface pressure, pi, the amine function in PE extends 1-2 A further into the subphase than those of the methylated headgroups. Not only is the exposure of the amine moiety to water in PE thus larger than that of the other lipids, but also the phosphate and lipid backbone of PE are more hydrated than that of PC. Overall, the PE headgroup hydration is approximately 25% larger than that of PE-N-Me, PE-N-Me2 or PC. The main reason for these differences resides in their distinct capabilities to donate hydrogen bonds, but differences in the hydrophobicities of the amine functions on the lipid headgroups may also play a role. While the impact of amine methylation on the headgroup interaction with the water subphase appears rather straightforward, there are also differences in lipid backbone organization and acyl chain packing. The results presented here provide a deeper understanding of lipid conformation as the hydrophobicity of the terminal headgroup fragment is systematically altered and may also impact on our understanding of the molecular details of membrane fusion.
利用表面敏感X射线散射技术，评估了完全水合磷脂分子构象及其与水库相互作用中的细微差异，这些差异是作为头部基团甲基化的函数来评估的。为了进行这种结构和功能的比较，研究了水表面单分子层中的二酰基磷脂酰乙醇胺（PEs）及其单甲基、二甲基和三甲基化（二酰基磷脂酰胆碱，PC）衍生物。虽然这些脂质的分子结构非常相似，但它们的细微差别导致其整体组织存在惊人的巨大差异。与表面压力π无关，PE中的胺官能团比甲基化头部基团的胺官能团向亚相延伸1-2埃。因此，PE中胺部分暴露于水的程度不仅比其他脂质大，而且PE的磷酸盐和脂质主链比PC更水合。总体而言，PE头部基团的水合程度比PE-N-Me、PE-N-Me2或PC大约大25%。这些差异的主要原因在于它们提供氢键的不同能力，但脂质头部基团上胺官能团的疏水性差异也可能起作用。虽然胺甲基化对头部基团与水亚相相互作用的影响似乎相当直接，但脂质主链组织和酰基链堆积也存在差异。这里给出的结果提供了对脂质构象更深入的理解，因为末端头部基团片段的疏水性被系统地改变，并且也可能影响我们对膜融合分子细节的理解。
