Figure 6.

Electron cryo-tomograms of a funnel-shaped deformation in the liposomal membrane induced by interaction with virions at pH 5.5. Also see Supplementary Movie 3. (A) The virus has grabbed hold of a liposome and drawn its membrane towards the viral envelope. A putative opening at the funnel's mouth is indicated by the white arrowheads in slice 1. The viral envelope appears to be intact; 5.3 nm-thick serial sections are shown. Samples have been acidified to pH 5.5 for 5 min; 50 nm scalebar. (B) A cross-sectional density plot (path indicated by black arrowheads in (A), slice 1) maps the ∼5 nm-wide channel through the lipid funnel. The channel is lined by the liposomal bilayer with 3–4 nm leaflet spacings. (C) A 10 nm-thick volume section shows density that is interpreted to be HA spikes in a ‘Y' shaped conformation (white arrowheads) coordinating the liposomal funnel. Density rendered using Chimera. Inset shows a schematic of the key density features.