Fig. 7: Schematic representation of viral spike protein-mediated membrane fusion.

The process occurs through four distinct stages: (1) pre-fusion, (2) transition, (3) intermediate, and (4) post-fusion states. The antibody 3D1 (red) binds specifically to the hinge region connecting the central helix and fusion peptide (FP), which adopts a transition-state conformation during the pre-fusion to intermediate stage conversion.