The structure of CoV virion and S protein, (A) Depiction of the CoV virion; (B) Depiction of S protein. A single S protein is depicted as a rectangle, and relevant structural features are highlighted as follows: N-terminal receptor binding domain (N-RBD) in dark blue; C-RBD in brown; cleavage sites (CS) 1 and 2, fusion peptide (FP) in red, heptad repeat (HR) regions 1 and 2 in green; transmembrane span (TM) depicted as membrane bilayer; cytoplasmic tail (CT) in light blue.; (C) Structure of the MHV N-RBD in complex with its CEACAM receptor.; (D) Structure of the SARS C-RBD in complex with its ACE2 receptor.; (E) Structure of the post-fusion HR1-HR2 bundle [7].