SARS-CoV recognizes its entry receptor hACE2 at the surface of type II pneumocytes using SB, which shares ∼75% overall amino acid sequence identity with SARS-CoV-2 SB and 50% identity within their receptor-binding motifs (RBMs). Previous studies also showed that the host proteases cathepsin L and TMPRSS2 prime SARS-CoV S for membrane fusion through cleavage at the S1/S2 and at the S2′ sites.