FIG 7.

Coronavirus spike proteins. (A) Diagram of coronavirus spike proteins. NTD, N-terminal domain; HRN, N-terminal heptad repeat; HRC, C-terminal heptad repeat. Group indicates the CoV genus and group. (B) Amino acid sequence alignment of S1 subunits of different betacoronaviruses. The letters with red underlining and red arrows are the contacting residues of MHV S protein with mouse CEACAM1a, while the letters with black underlining and black arrows are the sugar binding residues of BCoV S protein. The similarity of S1 among group A betacoronaviruses is about 71.9%, whereas the similarity of S1 among different group betacoronaviruses is about 29.4%.