Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, CA, USA.
SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
Nat Struct Mol Biol. 2023 Feb;30(2):167-175. doi: 10.1038/s41594-022-00898-1. Epub 2023 Jan 9.
Lipids in biological membranes are thought to be functionally organized, but few experimental tools can probe nanoscale membrane structure. Using brominated lipids as contrast probes for cryo-EM and a model ESCRT-III membrane-remodeling system composed of human CHMP1B and IST1, we observed leaflet-level and protein-localized structural lipid patterns within highly constricted and thinned membrane nanotubes. These nanotubes differed markedly from protein-free, flat bilayers in leaflet thickness, lipid diffusion rates and lipid compositional and conformational asymmetries. Simulations and cryo-EM imaging of brominated stearoyl-docosahexanenoyl-phosphocholine showed how a pair of phenylalanine residues scored the outer leaflet with a helical hydrophobic defect where polyunsaturated docosahexaenoyl tails accumulated at the bilayer surface. Combining cryo-EM of halogenated lipids with molecular dynamics thus enables new characterizations of the composition and structure of membranes on molecular length scales.
生物膜中的脂质被认为是具有功能组织的，但很少有实验工具可以探测纳米级膜结构。我们使用溴化脂质作为冷冻电镜的对比探针，以及由人源 CHMP1B 和 IST1 组成的 ESCRT-III 膜重塑系统，观察到高度收缩和变薄的膜纳米管内小叶层和蛋白质定位的结构脂质模式。这些纳米管与无蛋白的、平坦的双层膜在小叶层厚度、脂质扩散率以及脂质组成和构象不对称性方面有明显的不同。对溴化硬脂酰二十二碳六烯酰磷酸胆碱的模拟和冷冻电镜成像表明，一对苯丙氨酸残基如何在外小叶层上标记出一个螺旋状的疏水性缺陷，其中多不饱和二十二碳六烯酰尾巴在双层膜表面聚集。因此，将卤化脂质的冷冻电镜与分子动力学相结合，使我们能够在分子长度尺度上对膜的组成和结构进行新的表征。
