STRUCTURE OF A FLUID DIOLEOYLPHOSPHATIDYLCHOLINE BILAYER DETERMINED BY JOINT REFINEMENT OF X-RAY AND NEUTRON-DIFFRACTION DATA .3. COMPLETE STRUCTURE
STRUCTURE OF A FLUID DIOLEOYLPHOSPHATIDYLCHOLINE BILAYER DETERMINED BY JOINT REFINEMENT OF X-RAY AND NEUTRON-DIFFRACTION DATA .3. COMPLETE STRUCTURE
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DOI：
10.1016/s0006-3495(92)81849-0
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发表时间：
1992-02-01
影响因子：
3.4
通讯作者：
WHITE, SH
中科院分区：
文献类型：
--
作者：
WIENER, MC;WHITE, SH
本文报道了1，2-二油酰基-3-甘油-3-磷胆碱在L(α)相(66%RH，23℃)中的完整结构。之前获得的结构细节需要大量的中子衍射实验，使用的是许多特定的氚磷脂同构体(Buldt等人，1978年)。自然(长)。271：182-184)。联合精炼方法通过利用独立的中子和X射线数据集，最大限度地减少了特定的氢化。该方法产生由一系列多原子片段组成的准分子结构，每个片段由一个或几个高斯分布表示，其位置和宽度可被确定为0.06到0.52埃(不包括亚甲基区)。DOPC在66%RH(5.36+/-0.08水分/脂)的图像与先前通过结构和光谱研究确定的双层结构的许多方面一致。这种结构最显著的特征是由准分子碎片的高斯包络的宽度和重叠所表明的大量的跨双层热运动。我们讨论了用水的热运动来描述碳氢化合物渗透层的最小有效厚度的“动态双层厚度”。热运动的梯度存在于远离甘油主链的任一方向上增加，甘油主链是双层的最受限制的部分。在我们实验的水合水平上，我们清楚地揭示了相对双分子层的头基之间的空间相互作用。准分子结构的一个有用的结果是，使用组成和体积数据以及特殊假设计算的双分子层内的平均边界可以与主要结构基团的位置相关。对于Luzzati‘s d(I)(Luzzati和Husson)，可以确定常用的几种“双分子层厚度”的胆碱的位置。1962年。J.细胞生物学。12：207219)和Small‘s d(L)的甘油(Small.1967年。J.Lipid Res.8：551-556)。我们不知道这些关系是否会在其他水合作用或其他脂质中成立。特别令人感兴趣的是，羰基的位置标志着碳氢化合物/主基的平均边界。然而，必须强调的是，由于双层的热运动，双层的这一区域通常必须被描述为一个混乱的化学不均匀区域。
We present in this paper the complete structure of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) in the L(alpha) phase (66% RH, 23-degrees-C) obtained by the joint refinement of neutron and x-ray lamellar diffraction data. The structural details obtained have previously required a large number of neutron diffraction experiments using numerous specifically-deuterated phospholipid isomorphs (Buldt et al., 1978. Nature (Lond.). 271:182-184). The joint-refinement approach minimizes specific deuteration by utilizing independent neutron and x-ray data sets. The method yields a quasimolecular structure consisting of a series of multiatomic fragments that are each represented by one or several Gaussian distributions whose positions and widths can be determined to within 0.06 to 0.52 angstrom exclusive of the methylene region. The image of DOPC at 66% RH (5.36 +/- 0.08 waters per lipid) is consistent with many aspects of bilayer structure previously determined by structural and spectroscopic studies. The most striking feature of the structure is the large amount of transbilayer thermal motion suggested by the widths and overlaps of the Gaussian envelopes of the quasimolecular fragments. We discuss the "dynamic bilayer thickness" which describes the minimum effective thickness of the hydrocarbon permeability barrier in terms of the thermal motion of the water. A gradient of thermal motion exists that increases in either direction away from the glycerol backbone which is the most constrained portion of the bilayer. The steric interactions between headgroups of apposed bilayers, expected at the hydration level of our experiments, are clearly revealed. A useful consequence of the quasimolecular structure is that average boundaries within bilayers calculated using composition and volumetric data and ad hoc assumptions can be related to the positions of the principal structural groups. Several measures of "bilayer thickness" in common use can be identified as the positions of the cholines for Luzzati's d(I) (Luzzati and Husson. 1962. J. Cell Biol. 12:207-219) and the glycerols for Small's d(L) (Small. 1967. J. Lipid Res. 8:551-556). We do not know if these relations will be true at other hydrations or for other lipids. Of particular interest is the fact that the position of the carbonyl groups marks the average hydrocarbon/headgroup boundary. It must be emphasized, however, that this region of the bilayer must be generally characterized as one of tumultuous chemical heterogeneity because of the thermal motion of the bilayer.