Class I Viral Fusion Glycoproteins: Structural Insights into Viral Entry Strategies and Immune Evasion

Class I viral glycoproteins (GP) facilitate entry via the catalytic fusion of the viral envelope with host cell membrane through irreversible conformational changes in the viral GP. Outside of their functions in entry, these GPs often contribute to viral pathogenesis through antibody evasion and direct modulation of the host immune response. In this thesis, we employed structural and biophysical techniques to generate insights into Class I viral GP-mediated entry strategies and immune evasion with the aim of defining molecular targets for fusion inhibition and rational vaccine design. We first set out to identify the stabilization strategies that promote the adoption of the final irreversible six-helix bundle conformation necessary for Class I viral fusion. We characterized structural features of several post-fusion Class I viral entry GPs; we found that viruses that fuse in a pH-dependent manner utilize carboxyl-carboxylate interactions to stabilize the Class I entry GP during fusion, whereas viruses that fuse in a pH-independent manner use a distinct strategy involving classic electrostatic interactions to provide the required stability. Our results provide the basis for future studies aimed at targeting the inhibition of viral fusion through the destabilization of the post-fusion conformation. The next set of studies focuses on generating new insights into two-component Class I entry systems. We provide a structural description of the hemagglutinin-esterase (HE) GP from the infectious salmon anemia virus (ISAV), generating insights into the ISAV fusion mechanism and defining a molecular blueprint for the rational design of ISAV entry inhibitors that target the viral receptor binding pocket. Our final set of studies illustrates the structural determinants of immunodominance associated with the Class I viral fusion GP from HIV-1. Using X-ray crystallography, we demonstrate that the HIV-1 gp41 immunodominant region 1 (IR1) presents two distinct conformations to the host humoral immune system, potentially driving an ineffective response.Ph.D.2020-07-10 00:00:0