Lipid specificity of action of SARS-CoV-2 fusion peptide fragments on model membranes

The study focuses on investigating the interaction of SARS-CoV-2 fusion peptide fragment with model membranes of various lipid composition to elucidate the molecular mechanisms of peptide-derived membrane fusion. The work utilized the short fragment of SARS-CoV-2 fusion peptide which is homologous to 816-827 region of the native SARS-CoV-2 FP (FP _816-827 ) and contains the highly conserved LLF motif responsible for membrane fusion, and its ineffective analogue (mFP _816-827 ), where LLF motif was replaced for AAA. Using fluorescence fusion assay, it was demonstrated that the LLF motif plays a key role in inducing liposome fusion, whereas its replacement completely abolishes this capability. The fusogenic activity of the peptide strictly depended on the vesicle lipid composition. It was potentiated by phosphatidylethanolamine and inhibited by phosphatidylserine. Molecular dynamics revealed that both peptides predominantly adopt an α-helical conformation; however, the native peptide interacts more strongly with the hydrophobic core of the membrane by increasing peptide-lipid hydrophobic contacts, while the mutant version exhibits a more superficial localization. Differential scanning microcalorimetry data indicated that the ability of FP _{816- 827} to disturb lipid packing increased with decreasing membrane lipid tail length. The molecular mechanisms underlying the fusogenic activity of the SARS-CoV-2 fusion peptide were identified, specifically its ability to cluster phospholipid head groups in its own vicinity. As a result, local regions with positive spontaneous curvature are formed in the outer monolayer, facilitating membrane fusion. The findings highlight the role of membrane composition and lipid architecture in the mechanism of viral fusion with host cells.