Reverse-engineering a viral Swiss army knife: Crimean-Congo hemorrhagic fever virus glycoprotein functions in assembly, entry, and in vivo pathogenesis

The nairovirus Crimean-Congo hemorrhagic fever virus (CCHFV) causes severe, lethal hemorrhagic disease. CCHFV is the most prevalent tickborne virus that causes human disease and is endemic in countries across Europe, Asia, and Africa. No FDA-approved countermeasures are currently available for this NIAID priority pathogen. As in other bunyaviruses, the viral M segment of CCHFV encodes the glycoprotein precursor, GPC, which undergoes an especially complicated series of co- and post-translational proteolytic processing steps to generate multiple membrane-anchored, membrane-associated, and secreted glycoproteins. The overarching goal of this highly interwoven collaborative project is to address the critical gaps in our understanding of the architecture and assembly of the membrane-bound, virion-incorporated, and secreted glycoprotein components and complexes, and their functions in virion assembly, entry, host cell subversion, and disease. The collaborative team is anchored by K. Chandran (Einstein; BSL-2 virus models, genetic approaches, mechanistic virology, antibody discovery), J. McLellan (UT-Austin; structural virology, protein engineering), E. Harris (UC-Berkeley; virus-host interactions underlying pathogenesis, viral toxins), and A. Herbert and S. Monticelli (USAMRIID/The Geneva Foundation; mechanisms of infection and pathogenesis by authentic viruses at BSL-4). We also leverage the unique expertise of S. Sidoli (Einstein; mass spectrometry). Rigorous preliminary research by our interdisciplinary team has uncovered evidence that GP38 is both an integral component of the CCHFV entry glycoprotein complex and a secreted `toxin' that can subvert host endothelial barriers to cause vascular leak and/or facilitate viral dissemination. Building on these and other findings, we will determine high-resolution structures of CCHFV glycoprotein complexes and discover novel human monoclonal antibodies (Aim 1); elucidate mechanisms of CCHFV assembly, entry, and antibody action (Aim 2); and uncover entry-independent mechanisms of viral pathogenesis mediated by CCHFV GP38 and investigate the mechanisms by which anti-GP38 antibodies protect against CCHV infection and disease (Aim 3). We expect to deliver analyses of the structure, assembly, and functions of the `Swiss army knife' that is the CCHFV glycoprotein complex at an unprecedented level of molecular detail and identify viral Achilles' heels for the development of urgently needed CCHFV medical countermeasures.