Molecular-scale insights into the lipid–leaflet, lipid–lipid and lipid–protein dynamics that generate extreme membrane curvature could clarify the mechanisms of membrane remodeling. A better understanding of membrane and lipid structure during remodeling is crucial to understanding both the mechanisms of membrane remodeling and, more broadly, the interactions between proteins and membranes. Further, the structural evolution of lipids and lipid bilayers during these processes are challenging to study, as is quantifying the energetic contributions of individual lipid species to membrane remodeling. However, the precise mechanisms by which proteins generate mechanical force to catalyze membrane fission, fusion and shape changes remain elusive. The regulated activity of these membrane-remodeling machines drives processes such as vesicular traffic and organelle homeostasis. Combining cryo-EM of halogenated lipids with molecular dynamics thus enables new characterizations of the composition and structure of membranes on molecular length scales.Ĭells use molecular machines to form and remodel their membrane-defined compartments’ compositions, shapes and connections.

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. These nanotubes differed markedly from protein-free, flat bilayers in leaflet thickness, lipid diffusion rates and lipid compositional and conformational asymmetries. 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. Lipids in biological membranes are thought to be functionally organized, but few experimental tools can probe nanoscale membrane structure.

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