Yang Lin, Huang Huey W
National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973, USA.
Biophys J. 2003 Mar;84(3):1808-17. doi: 10.1016/S0006-3495(03)74988-1.
We constructed the electron density distribution from the x-ray diffraction of a phase of phospholipid that exhibited rhombohedral symmetry. To determine the phases of the diffraction amplitudes, we first extended the well-known one-dimensional swelling method for planar bilayers to a three-dimensional method applicable to a layered system containing in-plane structures, such as rhombohedral structures. The complete phase determination was accomplished by a combination of the swelling method and Luzzati's pattern recognition method. The constructed electron density distribution showed that in each unit cell, two apposed monolayers merged across the water layer and developed into an hourglass structure consistent with a postulated membrane fusion intermediate state called a stalk. The observation of the stalk structure lends a strong support to the stalk hypothesis for membrane fusion and opens a way to measure the structural parameters in the fusion pathway.
我们通过对呈现菱面体对称性的磷脂相进行X射线衍射构建了电子密度分布。为了确定衍射振幅的相位，我们首先将适用于平面双层的著名一维溶胀方法扩展为适用于包含面内结构（如菱面体结构）的层状系统的三维方法。通过溶胀方法和卢扎蒂模式识别方法的结合完成了完整的相位确定。构建的电子密度分布表明，在每个晶胞中，两个相对的单层跨水层合并并发展成沙漏结构，这与一种被称为茎的假定膜融合中间状态一致。茎结构的观察为膜融合的茎假说提供了有力支持，并为测量融合途径中的结构参数开辟了道路。
