Fig. 9.

A hypothetical model of membrane fusion between SARS-CoV and host cells showing involvement of the three putative fusion peptides, FP, IFP and PTM. Upon activation by receptor binding of the S1 domain, the FP (blue color) and IFP (red color) of the S2 domain of the fusion protein insert into host cells causing folding back of the HR1 (green color) and HR2 (yellow color) into six helix bundle. The aromatic residue rich PTM domain (magenta color) and the TM domain residing on the viral membrane provide a contiguous track of hydrophobic helical structures with HR domains and fusion peptides. Such an arrangement may facilitate the mixing of lipid molecules between the two membranes leading to the fusion of the viral and host cells.