Strikingly Different Roles of SARS-CoV-2 Fusion Peptides Uncovered by Neutron Scattering

Abstract

Coronavirus disease-2019 (COVID-19), a potentially lethal respiratory illness caused by the coronavirus SARS-CoV-2, emerged in the end of 2019 and has since spread aggressively across the globe. A thorough understanding of the molecular mechanisms of cellular infection by coronaviruses is therefore of utmost importance. A critical stage in infection is the fusion between viral and host membranes. Here, we present a detailed investigation of the role of selected SARS-CoV-2 Spike fusion peptides, and the influence of calcium and cholesterol, in this fusion process. Structural information from specular neutron reflectometry and small angle neutron scattering, complemented by dynamics information from quasi-elastic and spin−echo neutron spectroscopy, revealed strikingly different functions encoded in the Spike fusion domain. Calcium drives the N-terminal of the Spike fusion domain to fully cross the host plasma membrane. Removing calcium, however, reorients the peptide back to the lipid leaflet closest to the virus, leading to significant changes in lipid fluidity and rigidity. In conjunction with other regions of the fusion domain, which are also positioned to bridge and dehydrate viral and host membranes, the molecular events leading to cell entry by SARS-CoV-2 are proposed. ; Financial support for consumables was also provided by the Science and Technology Facilities Council (U.K.). N.R.Z. was supported by Wellcome Trust grant WT 207455/Z/17/Z. Part of the lipid extraction activity was funded by the ANR/NSF-PIRE project REACT (Research and Education in Active Coatings Technologies for Human Health). The National Deuteration Facility in Australia is partly funded by The National Collaborative Research Infrastructure Strategy (NCRIS), an Australian Government initiative. We gratefully acknowledge M. Jourdan and J. Dejeu (Université Grenoble Alpes) for access to the CD instrument; J. Carrascosa-Tejedor for help in the analysis of the SNR data collected; and Prof. E. Guzman, Prof. P. Luzio, Prof. D. Owen, and Dr. J. ...