Negatively Charged Lipids Provide a Preferred Membrane Ecosystem for Higher Fusogenicity of SARS-CoV-2 Internal Fusion Peptide.

Enveloped viruses employ membrane fusion to infect the host cells. Viral fusion glycoproteins are the discernible engines of fusion, since they undergo massive conformational changes that bring the viral and host membranes together, inducing the formation of a stalk, hemifusion diaphragm, and eventually a fusion pore. Lipid composition tunes how easily the fusion protein can embed its fusion peptide, deform the bilayer, and stabilize the intermediates. Unlike other class I viruses, the severe acute respiratory syndrome coronavirus (SARS-CoV-2) spike (S) protein harbors multiple hydrophobic, fusion peptide-like sequences within its S2 subunit that collectively enhance its fusogenicity and infectivity. In this present work, we have studied the effect of a short region of the internal fusion peptide (IFP) of SARS-CoV-2 on the polyethylene glycol-induced fusion of zwitterionic and negatively charged small unilamellar vesicles. A better understanding of the mechanistic role of IFP in membrane fusion is obtained by analyzing the kinetic data of fusion observables, such as lipid mixing, content mixing, and content leakage in a one-intermediate, three-state sequential fusion model. In the negatively charged membranes, IFP promotes the rate constants as well as the extent of hemifusion and pore formation, whereas it promotes only fusion rates in zwitterionic membranes. Taken together, our findings highlight that the lipidic ecosystem of the membrane determines the role of the peptide in membrane organization and dynamics and its impact on membrane fusion.