Figure 4.

Target membrane deformations in virion–liposome complexes observed by ECT. Samples had been acidified at pH 5.5 for 5–8 min. Microscope defocus was set at 3–5 μm; 5.3 nm-thick slices through reconstructed cryo-tomographic density are shown. Scalebars 50 nm. (A) At early stages of docking, the liposomal bilayer is pulled into ∼5 nm-wide dimples (black arrowheads). (B) Some liposomes make glancing contacts (arrowhead in slice 3) with the viral envelope. (C) Liposomes can form extended planar contacts with virus envelope. (D) The liposome in this complex is engaged by two virions, one above and one to the left hand side. The liposome in this case forms a nearly planar contact with the virus on the left and appears to be coordinated by HA. The boxed HA spike in slices 2 and 3 exhibits density in a ‘Y' shape bridging the virus surface and liposome. This resembles features seen at virus membrane junctions in HSV-1 entry studies (Maurer et al, 2008). The interaction with the upper virus is more localized, with the liposomal membrane being pinched into an acute angle (arrowhead, slice 1).