EFFECT OF LIPID COMPOSITION AND CALCIUM IONS ON THE STRUCTURE AND FUNCTION OF SARS-CoV-2 FUSION PEPTIDES

Vol 3, 2025 - 330763
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Abstract

Coronaviruses enter cells through the fusion of their viral and host cell membranes in a process mediated by short, hydrophobic segments called fusion peptides (FPs) located within the Spike (S) protein. FPs modulate membrane dynamics, enabling the virus to overcome energetic barriers and successfully merge both membranes. This study investigates how lipid composition, pH, cholesterol, and calcium ions affect the structure and function of SARS-CoV and SARS-CoV-2 fusion peptides using fluorescence spectroscopy, circular dichroism, and electron paramagnetic resonance. Four FPs were examined: 1FPuH7 and 2FPuH7, corresponding to the upstream fusion peptides from SARS-CoV and SARS-CoV-2, respectively; FPH7, the canonical FP; and IFPH7, the internal fusion peptide. The results revealed that the fusogenic activity and membrane-ordering effects were significantly enhanced in negatively charged membranes containing either phosphatidylserine (POPS) or phosphatidylglycerol (POPG), with highest activity generally at acidic pH (5.0). IFPH7 was an exception, showing maximal activity at neutral pH (7.4), highlighting pH-dependent functional diversity of FPs. Secondary structure analysis revealed that peptides remained largely disordered upon membrane binding, with subtle but functionally relevant β-strand formation in anionic membranes. In contrast, micelles promoted α-helical structures, particularly in IFPH7. Cholesterol modulated peptide activity in a sequence-dependent manner: 1FPuH7 fusogenicity increased linearly with cholesterol, whereas FPH7 activity declined at high cholesterol levels, suggesting that excessive membrane rigidity can inhibit the activity of certain peptides. Cholesterol also enhanced membrane ordering, especially at the headgroup level, with peptide-specific effects on fusion efficiency. Calcium ions consistently inhibited the fusogenic activity across all peptides, with the strongest inhibition in POPS-containing membranes at neutral pH. While calcium minimally affected peptides' secondary structures, it modestly enhanced lipid ordering at the headgroup level and reduced membrane surface charge, thereby limiting peptide-membrane interactions. This study highlights the complex interplay between fusion peptides and membrane components, emphasizing how lipid composition, pH, cholesterol, and calcium ions can collectively regulate membrane fusion. These insights deepen our understanding of coronavirus entry mechanisms and may guide future therapeutic strategies targeting key factors involved in viral membrane fusion processes.

This study was financed by FAPERJ (processes 210.778/2021 and 211.816/2021) and in part by CAPES – Finance Code 001.

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Programme
18:30 to 20:00 on 10/30/2025
UNICAMP Multidiscip…
Institutions
  • 1 Universidade Estadual do Norte Fluminense Darcy Ribeiro
  • 2 UENF - Brasil
Track
  • 1. Protein Dynamics and Function
Keywords
Fusion peptides
Membrane fusion
SARS-CoV-2
Lipid composition
Calcium