Determination of the hydrocarbon core structure of fluid dioleoylphosphocholine (DOPC) bilayers by x-ray diffraction using specific bromination of the double-bonds: Effect of hydration
Determination of the hydrocarbon core structure of fluid dioleoylphosphocholine (DOPC) bilayers by x-ray diffraction using specific bromination of the double-bonds: Effect of hydration
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DOI：
10.1016/s0006-3495(98)77950-0
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发表时间：
1998-05-01
影响因子：
3.4
通讯作者：
White, SH
中科院分区：
文献类型：
--
作者：
Hristova, K;White, SH
流体脂质双层的烃核心（HC）结构的变化可以揭示双层如何响应肽和其他溶质的分配（Jacobs，R. E、和S. H.白色。1989.生物化学。28：3421-3437）。二油酰磷酸胆碱（DOPC）双层的HC的结构可以由双键的跨双层分布确定（Wiener，M. C.的方法，和S. H.白色。1992. Biophys. J. 61：434-447）。该分布表示双键位置在双层法线（z）上的时间平均投影，可以通过中子衍射和双键特定氘代（Wiener，M. C.的方法，G. I. King和S. H.白色。1991. Biophys. J. 60：568-576）。对于完全分辨的双层分布，可以通过X射线衍射和在DOPC sn-2酰基链的双键处的同晶溴标记获得分布的近似值（Wiener，M. C.的方法，和S. H.白色。1991.生物化学。30：6997-7008）。我们已经修改了溴标记的方式，允许确定在高含水量下观察到的双层分布。我们使用这种新方法来确定DOPC的双键溴标记物在每个脂质5.4至16沃茨的水合范围内的跨双层分布，这揭示了HC结构如何随着水合而变化。我们发现溴的跨双层分布可以用一对位于相对于双层中心z = +/-Z（Br）的1/e半宽A（Br）的高斯分布来描述。对于每个脂质从5.4沃茨到9.4沃茨的水合，Z（Br）从7.97 +/- 0.27埃降低到6.59 +/- 0.15埃，而A（Br）从4.62 +/- 0.62埃增加到5.92 +/- 0.37埃，与预期的水合诱导的HC厚度降低和每个脂质面积增加一致。在磷酸胆碱水合壳以类似于12沃茨/脂质填充后，我们观察到Z（Br）偏移至类似于7.3埃，表明水合壳完成后的明显结构变化。对于每个脂质12-16个沃茨的水合，溴分布在Z（Br）= 7.33 +/- 0.25埃和A（Br）= 5.35 +/- 0.5埃处保持恒定。在实验中获得的绝对尺度结构因子提供了一个机会，以测试所谓的流体减去方法的结构因子缩放。我们发现，该方法是相当令人满意的确定结构因子的相位，但不是他们的绝对值。
Changes in the structure of the hydrocarbon core (HC) of fluid lipid bilayers can reveal how bilayers respond to the partitioning of peptides and other solutes (Jacobs, R. E., and S. H. White. 1989. Biochemistry. 28:3421-3437). The structure of the HC of dioleoylphosphocholine (DOPC) bilayers can be determined from the transbilayer distribution of the double-bonds (Wiener, M. C., and S. H. White. 1992. Biophys. J. 61:434-447). This distribution, representing the time-averaged projection of the double-bond positions onto the bilayer normal (z), can be obtained by means of neutron diffraction and double-bond specific deuteration (Wiener, M. C., G. I. King, and S. H. White. 1991. Biophys. J. 60:568-576), For fully resolved bilayer profiles, a close approximation of the distribution could be obtained by x-ray diffraction and isomorphous bromine labeling at the double-bonds of the DOPC sn-2 acyl chain (Wiener, M. C., and S. H. White. 1991. Biochemistry. 30:6997-7008). We have modified the bromine-labeling approach in a manner that permits determination of the distribution in under-resolved bilayer profiles observed at high water contents. We used this new method to determine the transbilayer distribution of the double-bond bromine labels of DOPC over a hydration range of 5.4 to 16 waters per lipid, which reveals how the HC structure changes with hydration. We found that the transbilayer distributions of the bromines can be described by a pair of Gaussians of 1/e half-width A(Br) located at z = +/-Z(Br) relative to the bilayer center. For hydrations from 5.4 waters up to 9.4 waters per lipid, Z(Br) decreases from 7.97 +/- 0.27 Angstrom to 6.59 +/- 0.15 Angstrom, while A(Br) increased from 4.62 +/- 0.62 Angstrom to 5.92 +/- 0.37 Angstrom, consistent with the expected hydration-induced decrease in HC thickness and increase in area per lipid. After the phosphocholine hydration shell was filled at similar to 12 waters per lipid, we observed a shift in Z(Br) to similar to 7.3 Angstrom, indicative of a distinct structural change upon completion of the hydration shell. For hydrations of 12-16 waters per lipid, the bromine distribution remains constant at Z(Br) = 7.33 +/- 0.25 Angstrom and A(Br) = 5.35 +/- 0.5 Angstrom. The absolute-scale structure factors obtained in the experiments provided an opportunity to test the so-called fluid-minus method of structure-factor scaling. We found that the method is quite satisfactory for determining the phases of structure factors, but not their absolute values.