Extended Data Fig. 4: Compositional analysis of lipid bilayers in cryo-EM reconstructions and biophysical characterization of brominated lipids.

(a) Analysis of the structure and composition of the membrane-protein contact sites and the gaps between contact sites. To improve the signal to noise ratio, each Z slice of the cryo-EM reconstruction was rotated to align it with the previous frame, resulting in an ‘uncoiled’ nanotube that was projected in Z. (b) Radial averages for 30 ° at the contact sites (left) and between the contact sites (right), where the protein is farthest from the bilayer. Radial averages for cryo-EM reconstructions at the contact sites (c) and at the gaps between contact sites (d). Cryo-EM reconstructions from samples in which different fractions of the SDPC was brominated. (e) Quantification of the excess intensity in each leaflet, with normalization per leaflet. Reducing the SDPC-Br concentration results in attenuated Br scattering in each leaflet. The reduction is not linear with SDPC-Br concentration, suggesting that SDPC-Br is somewhat enriched in the lipid bilayer nanotubes relative to SDPC. Data are plotted as the mean from independent calculations from each of the two half maps, and error bars represent the standard deviation from the independent half maps. (f) Visualization of the SDPC-Br titration along a Z line scan of the outer leaflet from vertical slices of the cryo-EM reconstructions (g). (h, i) Langmuir pressure-area isotherms show that brominated lipids behave similarly to their unbrominated analogs in lipid monolayers. Although brominated lipids are less compressible than the unsaturated lipids, they are much more compressible than saturated lipids like DSPC. Data for graphs in c–e, g–i are available as source data.

Source data