Elucidation of Assembly and Budding Mechanisms of SARS-CoV-2

Project Summary Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus responsible for the ongoing human pandemic (COVID-19) that has been classed as a Public Health Emergency of International Concern by the World Health Organization (WHO). There is an urgent demand for SARS-CoV-2 research to facilitate the development of therapeutics, understand viral replication and pathogenesis, and determine how the virus spreads from cell-to-cell as well as patient to patient. Coronaviruses such as SARS and MERS are among the most dangerous pathogens on Earth, with high fatality rates and lack of viable therapeutics or vaccines. They are classified as category C pathogens by the NIH due to their ease of production and dissemination with the potential of high morbidity and mortality. Detailed mechanistic studies on the dynamics of SARS-CoV-2 replication and viral shedding (i.e., budding) may inform identification of new drug targets in the viral life cycle and enrich our understanding of how this zoonotic pathogen utilizes host cell lipids to build the viral lipid envelope. The Stahelin and Voth laboratories, building on collaborations with each other and specific expertise in biochemistry, biophysics and computational studies of virus assembly, will use experimental in vitro and cellular studies integrated with computational analysis to investigate the central hypothesis in this grant: that selective lipid-protein interactions drive the assembly and budding of the M (membrane) and N (nucleoprotein) of SARS- CoV-2. In two specific aims, we will (i) determine the cellular and biophysical mechanisms by which SARS-CoV- 2 M form virus particles in silico, in vitro and in human cells and (ii) determine how N lipid binding drives localization that contributes to formation of new viral particles. These studies will be integrated with structural biology of M (Browhan laboratory) and N (Ollmann Saphire laboratory) and also be validated with authentic SARS-CoV-2 in a BSL-3 facility in collaboration with the Kuhn laboratory. These questions will be studied in a tightly integrated approach using structural and in vitro quantitative techniques to assess lipid-protein and protein-protein interactions and cellular assays to tease apart the molecular underpinnings of viral protein interactions necessary for viral budding and infection. Computationally, we will use coarse-grained (CG) molecular dynamics (MD) simulations to characterize the assembly process on the membrane and to identify a set of models for further refinement through all-atom (AA) MD simulations. This innovative and integrated approach will not only provide careful validation of the results, but also provide detailed structural insights into the lipid-protein and protein-protein interactions governing the assembly and budding of SARS-CoV-2. The protein interfaces of M and N identified in these studies, which will be key for virus assembly and spread, will inform future drug targeting against SARS-CoV-2 and other coronaviruses.