Understanding pH-dependent receptor utilization of Lassa virus

The Old-World Arenavirus Lassa (LASV) can cause severe hemorrhagic Lassa fever (LF), which is associated with significant morbidity and mortality in West Africa every year. As the most exported hemorrhagic fever, LASV also poses a significant global health risk. LF is recognized as a "Priority disease" by the World Health Organization (WHO) and the Coalition for Epidemic Preparedness Innovations (CEPI). The trimeric glycoprotein complex (GPC) is the only viral protein expressed on the virion surface and responsible for LASV cell entry. Each monomer within the trimer is composed of the non-covalently associated stable signal peptide, the receptor-binding subunit, GP1, and the fusion machinery, GP2. LASV sequentially utilizes two host receptors for cell entry, the matriglycosylated alpha-dystroglycan (matri-α-DG) at the cell surface and the lysosomal-associated membrane protein 1 (LAMP1) in the endosome during endocytosis of the virion. The receptor switch requires an acidic pH-induced conformational rearrangement of the GPC trimer, called GPC priming. Structural biology has only captured atomic snapshots: prefusion GPC in complex with matriglycan, and then individual subunits: post-fusion GP2, and a low-pH incubated GP1 truncation presumed to be in the primed state. The inherent metastability of GPC has thwarted efforts to obtain high-resolution structures of trimeric GPC in priming states and the GPC:LAMP1 complex. In this project, we will fill in these important missing structures and illuminate pH-driven changes in the GPC trimer and mechanisms for receptor switching. The proposed structural work for this program is made feasible by a novel LASV GPC construct engineered by the PI that maintains native conformation at neutral pH and is capable of priming and LAMP1 binding at acidic pH, without dissociation of the GP1 and GP2 subunits. Importantly, insights from these studies can be applied to other medically relevant, pH-dependent receptor-switching arenaviruses, such as the ubiquitous Lymphocytic choriomeningitis virus and the rare, but potentially more fatal, Lujo virus.