inal 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