Table S3.

Measured distances in RCoV-NJ HE and MHV-S HE

RCoV-NJ HE	Distance, Å	B factor, Å2	MHV-S	Distance, Å	B factor, Å2
Na+	—	48.78	K+	—	51.87
Asp225-Oδ1	2.34	49.57	Asp230-Oδ1	2.61	45.26
Ser226-O	2.59	49.58	Ser231-O	2.31	45.41
(Gln227-Oε1)	3.43	47.15	Gln232-Oε1	3.06	46.96
Ser273-Oγ	2.56	50.96*	Ser278-Oγ	2.62	45.70
Glu275-O	2.34	52.23	Glu280-O	3.05	46.49
Leu277-O	2.36	48.94	Leu282-O	2.63	42.55
			H2O-2030	3.29	48.68

^*Coordination of Na⁺ by the side chain of Ser²⁷³ in RCoV-NJ is not certain. The side chain is modeled similar to Ser²⁷⁸ in MHV-S (pointing toward Na⁺) but different from Ser²⁷¹ in MHV-DVIM (pointing from Na⁺). Electron density is not definite here.