X-ray diffraction reconstruction of the inverted hexagonal (HII) phase in lipid-water systems.
X-ray diffraction reconstruction of the inverted hexagonal (HII) phase in lipid-water systems.
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DOI：
10.1021/bi00120a009
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发表时间：
1992-02
期刊：
影响因子：
2.9
通讯作者：
D. Turner;S. Gruner
中科院分区：
文献类型：
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作者：
D. Turner;S. Gruner
研究生物脂质-水系统中倒六方（HII）相的结构，以检查驱动多晶相行为的物理相互作用，并且也被认为在生物膜功能中发挥相关作用。导出了一种方法，该方法通过检查单个样品来产生 HII 相位衍射振幅的复杂相位因子。该方法应用于二油酰磷脂酰乙醇胺 (DOPE) + 水中的 HII 相的低分辨率傅里叶重建，特别是检查与假定的 HII 相圆形模型的偏差。研究发现，通过傅里叶重建确定的水核平均半径 Rw 与之前通过更耗时的传统方法获得的 Rw 测量值非常一致 [Tate, M. W., & Gruner, S. M. (1989) Biochemistry 28, 4245]。除了Rw的平均值外，还可以利用傅里叶重构来确定水核的真实形状。研究发现，当晶胞尺寸小于约 75 A 时，水核的圆形度在 Rw 的 5% 以内。然而，在 75 A 以上，一定的形状变形变得明显，径向非圆形度为 5-10%，这可能是由于将烃链填充到 HII 晶胞的各向异性环境中的熵成本增加所致 [Kirk, G. L., Gruner, S. M., & Stein D. E. (1984) 生物化学 23, 1093]。作为堆积各向异性的更直接的探测，DOPE + 十二烷和 DOPE + 角鲨烯系统的傅立叶重建与 DOPE 的重建进行了比较。已知这些油可以促进 HII 相的低温出现，大概是通过减少烃堆积应力来实现的。为了支持这一假设，观察到烷烃将水核松弛成圆形，甚至形成大晶格。此外，当添加烷烃时，脂质链末端附近的电子密度的各向异性会降低，这意味着烃堆积环境更加均匀，这与添加氘代癸烷时的中子衍射结果一致[Turner, D. C., Gruner, S. M., & Huang, J. (1992) Biochemistry (本期下一篇文章)]。
The structure of the inverted hexagonal (HII) phase in biological lipid-water systems is studied to examine the physical interactions which drive the polymorphic phase behavior and which are also thought to play a relevant role in biological membrane function. A method is derived which yields the complex phase factors of the HII phase diffraction amplitudes from examination of a single sample. This method is applied to a low-resolution Fourier reconstruction of the HII phase in dioleoylphosphatidylethanolamine (DOPE) + water, specifically to examine deviations from the presumed circular model of the HII phase. It is found that the average radius of the water core, Rw, as determined from a Fourier reconstruction, is in good agreement with previously measured values of Rw obtained from more time-consuming traditional methods [Tate, M. W., & Gruner, S. M. (1989) Biochemistry 28, 4245]. In addition to the average value of Rw, the Fourier reconstruction also can be used to determine the true shape of the water core. It is found that the water core is circular to within 5% of Rw when the unit cell size is less than approximately 75 A. Above 75 A, however, a definite shape deformation becomes apparent, with radial noncircularities of 5-10%, probably in response to the increased entropic cost of packing the hydrocarbon chains into the anisotropic environment of the HII unit cell [Kirk, G. L., Gruner, S. M., & Stein D. E. (1984) Biochemistry 23, 1093]. As a more direct probe of the packing anisotropy, Fourier reconstructions of DOPE + dodecane and DOPE + squalene systems were compared with the reconstruction of DOPE. These oils are known to promote the low temperature occurrence of the HII phase, presumably by a reduction in the hydrocarbon packing stress. In support of this hypothesis, the alkanes were observed to relax the water core to a circular shape for even large lattices. In addition, anisotropy of the electron density near the end of the lipid chains is reduced when alkane is added, implying a more uniform hydrocarbon packing environment, consistent with the results of neutron diffraction upon the addition of deuterated decane [Turner, D. C., Gruner, S. M., & Huang, J. (1992) Biochemistry (following paper in this issue)].