Leikin S, Kozlov M M, Fuller N L, Rand R P
Laboratory of Structural Biology, National Institutes of Health, Bethesda, Maryland 20892, USA.
Biophys J. 1996 Nov;71(5):2623-32. doi: 10.1016/S0006-3495(96)79454-7.
Diacylglycerol, a biological membrane second messenger, is a strong perturber of phospholipid planar bilayers. It converts multibilayers to the reverse hexagonal phase (HII), composed of highly curved monolayers. We have used x-ray diffraction and osmotic stress of the HII phase to measure structural dimensions, spontaneous curvature, and bending moduli of dioleoylphosphatidylethanolamine (DOPE) monolayers doped with increasing amounts of dioleoylglycerol (DOG). The diameter of the HII phase cylinders equilibrated in excess water decreases significantly with increasing DOG content. Remarkably, however, all structural dimensions at any specific water/lipid ratio that is less than full hydration are insensitive to DOG. By plotting structural parameters of the HII phase with changing water content in a newly defined coordinate system, we show that the elastic deformation of the lipid monolayers can be described as bending around a pivotal plane of constant area. This dividing surface includes 30% of the lipid volume independent of the DOG content (polar heads and a small fraction of hydrocarbon chains). As the mole fraction of DOG increases to 0.3, the radius of spontaneous curvature defined for the pivotal surface decreases from 29 A to 19 A, and the bending modulus increases from approximately 11 to 14 (+/-0.5) kT. We derive the conversion factors and estimate the spontaneous curvatures and bending moduli for the neutral surface which, unlike the pivotal plane parameters, are intrinsic properties that apply to other deformations and geometries. The spontaneous curvature of the neutral surface differs from that of the pivotal plane by less than 10%, but the difference in the bending moduli is up to 40%. Our estimate shows that the neutral surface bending modulus is approximately 9kT and practically does not depend on the DOG content.
二酰基甘油作为一种生物膜第二信使，是磷脂平面双层的强力扰动剂。它能将多层膜转变为反向六方相（HII），该相由高度弯曲的单分子层组成。我们利用HII相的X射线衍射和渗透压来测量掺杂不同量二油酰甘油（DOG）的二油酰磷脂酰乙醇胺（DOPE）单分子层的结构尺寸、自发曲率和弯曲模量。在过量水中平衡的HII相圆柱体的直径会随着DOG含量的增加而显著减小。然而，值得注意的是，在任何特定的水/脂比（小于完全水合）下，所有结构尺寸对DOG都不敏感。通过在一个新定义的坐标系中绘制HII相的结构参数随含水量的变化，我们表明脂质单分子层的弹性变形可以描述为围绕一个恒定面积的枢轴平面弯曲。这个分隔面包含30%的脂质体积，与DOG含量无关（极性头部和一小部分烃链）。随着DOG的摩尔分数增加到0.3，为枢轴表面定义的自发曲率半径从29 Å减小到19 Å，弯曲模量从大约11增加到14（±0.5）kT。我们推导了转换因子，并估计了中性表面的自发曲率和弯曲模量，与枢轴平面参数不同，这些是适用于其他变形和几何形状的固有属性。中性表面的自发曲率与枢轴平面的自发曲率相差不到10%，但弯曲模量的差异高达40%。我们的估计表明，中性表面弯曲模量约为9kT，实际上不依赖于DOG含量。
