Analysis of the Ebola virus glycoprotein

Ebola is among the most pathogenic of all known human viruses with mortality rates of up to 90%. Ebola is an enveloped virus with a single virally encoded glycoprotein studding the viral membrane. A model system was developed to study the function of this glycoprotein. We showed that the Ebola glycoprotein (EBO-GP) is responsible for mediating viral entry and that the cellular host range conferred by this protein is extremely broad. Interestingly, EBO-GP was not able to mediate entry into lymphoid cells suggesting the lack of a functional cellular receptor. The pH dependence of EBO-GP mediated entry was demonstrated, suggesting that the low pH environment of the endosome is the trigger for the conformational changes leading to membrane fusion. Epitope tagged forms of EBOGP suggest that the glycoprotein is proteolytically processed during maturation. We investigated this phenomenon by site-directed mutagenesis of a conserved dibasic region and demonstrated that EBO-GP is processed into two subunits, GP1 and GP2 that are covalently linked via a disulfide bond. Despite absolute conservation of the dibasic cleavage site in all strains of Ebola, efficient processing appears unnecessary for viral entry. Overexpression of EBOGP leads to a loss of adhesion in transfected cells. Flow cytometry revealed that the integrin family of adhesion proteins is downregulated from the surface of cells transfected with the Ebola glycoproteins, but not those of Subgroup A avian sarcoma and leukosis virus glycoprotein. Further investigation indicated that this downregulation of cell surface proteins is likely global rather than specific as all proteins tested were downregulated significantly. The downregulation of integrins in cells expressing EBO-GP is likely the cause for the loss of adhesion seen in these cells and we implicate it as a major component of viral pathogenesis in vivo.