Structural Mechanisms of Alphavirus Membrane Fusion

Alphaviruses, a group of enveloped RNA viruses, cause persistent arthritis and encephalitis among horses and humans. Currently, no licensed vaccine or antiviral therapy is available to prevent or cure the disease. A critical step in enveloped virus infection is membrane fusion between the viral and the host cellular membranes, a process leading to cytoplasmic delivery of the viral genome. Alphaviruses enter the host cell via receptor- mediated endocytosis. The viral E1 protein mediates membrane fusion through conformational changes upon acidification in the early endosomes. The other viral envelope protein, E2, functions as a molecular chaperon for the E1 protein during virus assembly and plays a role in virus capsid core uptake at the budding site and release after membrane fusion. We have obtained exciting, unprecedented images that captured robust alphavirus membrane fusion events with target liposomes by cryo-electron microscopy. Using coordinated biochemical, biophysical, cryo-electron microscopy, and cryo-electron tomography methods, we will investigate the molecular structures of the E1 and E2 proteins in a prototype alphavirus, Sindbis virus, at specific fusion stages. We will test specific predictions about the alphavirus membrane fusion mechanism based on our structural results by generating and characterizing mutants of the glycoproteins. We will test the fusion function of key mutations in the context of recombinant viruses. Completing this research will advance our understanding about how alphavirus glycoproteins promote membrane fusion.