Table S1.

Rmsd (angstrom) values (Cα-atoms only)

Domain	RCoV-NJ	BCoV-Mebus	MHV-DVIM
Membrane proximal domain
BCoV-Mebus	0.45
MHV-DVIM	0.29	0.33
MHV-S	0.25	0.35	0.27
Esterase domain*
BCoV-Mebus	0.25 (0.32)
MHV-DVIM	0.25 (0.32)	0.21 (0.26)
MHV-S	0.28	0.33	0.34
Lectin domain
BCoV-Mebus	0.45
MHV-DVIM	0.32	0.51
MHV-S	0.31	0.45	0.26

^*Values in parentheses refer to rmsd values of critical active site residues shown in Fig. 2A. No values could be calculated for active site residues of MHV-S HE because these were disordered in the structure.