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功能性组织的，但很少有实验工具可以探测纳米级膜结构。使用溴化脂质作为冷冻电镜的对比探针和由人 CHMP1B 和 IST1 组成的模型 ESCRT-III 膜重塑系统，我们在高度收缩和薄的膜纳米管内观察到小叶水平和蛋白质定位的结构脂质模式。这些纳米管在小叶厚度、脂质扩散速率以及脂质成分和构象不对称性方面与无蛋白质的扁平双层显着不同。溴化硬脂酰基-二十二碳六烯酰基-磷酸胆碱的模拟和冷冻电镜成像显示，一对苯丙氨酸残基如何在外叶上刻划出螺旋疏水缺陷，其中多不饱和二十二碳六烯酰尾部在双层表面积累。因此，将卤化脂质的冷冻电镜与分子动力学相结合，可以在分子长度尺度上对膜的组成和结构进行新的表征。