Identification and Analysis of Amino Acid Substitutions in Ebola Virus Glycoprotein Fusion Loop That Interfere With Infection

Abstract

The Ebola virus glycoprotein, GP, is responsible for the fusion of the virus membrane with that of its host target and the consequent entry of the virus into the cell cytosol. GP is expressed on the surface of the virus membrane as a trimer of dimers, each of which is formed through the post-translational furin cleavage of native GP into two subunits: GP1, which contains a receptor binding domain, and GP2, which contains the spring-loaded fusion machinery. GP1 also acts as a clamp to hold GP2 in its pre-fusion conformation. Host factors trigger the release of the GP1 clamp and cause the metastable α-helix coiled-coil of GP2 to extend, inserting the fusion loop into the target membrane. The extended coil then folds back in on itself to form a highly stable six-helix bundle that is coupled to virus membrane fusion and infection. I hypothesize that amino acid residues with hydrophobic side changes that reside at the tip of the fusion loop are necessary for virus membrane fusion. To test this, the effects of substitutions in these residues on GP assembly and infection have been evaluated. I found that substitution of arginine for tyrosine 535 in GP2 did not affect glycoprotein synthesis, cleavage, virus incorporation, or host factor interactions but is highly defective for infection. These findings demonstrate that GP Y535 is essential for Ebola virus infection and that the Y535R mutant likely confers a defect in virus membrane fusion.