Membrane Association, Conformation, and Dynamics of SARS-CoV/SARS-CoV-2 Spike Fusion Peptides in Lysolipid Micelles

Fusion peptides within the coronavirus (CoV) Spike glycoprotein interact with host membranes and contribute to the structural rearrangements required for membrane fusion. Here, we investigated the upstream fusion peptide (FPu) from severe acute respiratory syndrome (SARS)-CoV and the conserved internal fusion peptide (IFP) of SARS-CoV/SARS-CoV-2 in zwitterionic and anionic lysolipid micelles using steady-state and time-resolved fluorescence, circular dichroism (CD), electron spin resonance (ESR), and molecular dynamics (MD) simulations. Both peptides strongly associated with the micellar phase, with IFP displaying higher partition coefficients and a clearer preference for negatively charged micelles. FPu exhibited pronounced environment-sensitive fluorescence changes, whereas CD revealed greater α-helical propensity for IFP and higher conformational heterogeneity for FPu. ESR showed that both peptides restricted spin-probe rotational dynamics, with broader and stronger effects in anionic micelles, particularly under acidic pH. MD simulations further indicated dynamic micelle-bound topologies in which central peptide regions were preferentially lipid-associated and less solvent-exposed, while terminal regions remained more flexible. Together, the results demonstrate that peptide affinity, conformation, bound-state topology, and perturbation of micellar dynamics are related but non-equivalent properties, highlighting the importance of membrane composition and environmental conditions in modulating coronavirus fusion-peptide interactions.