Mechanism of membrane perforation in rotavirus cell entry

Cell entry of nonenveloped animal viruses requires translocation of a macromolecular assembly across a cellular membrane. Double-stranded RNA viruses introduce into the target cell an inner capsid particle that does not uncoat further. Instead, it extrudes capped viral mRNA by virtue of polymerase and capping activities within it. As described here, we used cryogenic electron tomography to visualize the full course of rhesus rotavirus entry, from cell attachment and virion uptake to release of the subviral particle. The cryo-tomograms and subtomogram averaging of classified subparticles link high-resolution structures of the virion and its components with time series from live-cell fluorescence microscopy. We outline the mechanism of each step in the entry process, including the membrane perforation step that transfers a subviral particle into the cytosol. Viruses that lack a lipid envelope need strategies to interact with and cross the outer membrane of a potential host cell. de Sautu et al. used cryo’electron tomography to visualize how the surface proteins of rhesus rotavirus interact with the plasma membrane to mediate viral entry into intact cells. Viral surface proteins executed two sequential membrane insertions and calcium flux events, first driving endocytosis of the virus and then maturation of viral particles and perforation of the endosomes that contain them. This in situ reconstruction illustrates how the structure of the viral surface proteins can induce the membrane changes and cellular signals needed for viral uptake. —Cheri Sirois