CoV uses its spike glycoprotein (S), a main target for neutralization antibody, to bind its receptor, and mediate membrane fusion and virus entry. Each monomer of trimeric S protein is about 180 kDa, and contains two subunits, S1 and S2, mediating attachment and membrane fusion, respectively. In the structure, N- and C- terminal portions of S1 fold as two independent domains, N-terminal domain (NTD) and C-terminal domain (C-domain) (Fig. 1a). Depending on the virus, either NTD or C-domain can serve as the receptor-binding domain (RBD). While RBD of mouse hepatitis virus (MHV) is located at the NTD14, most of other CoVs, including SARS-CoV and MERS-CoV use C-domain to bind their receptors15–19. MHV uses mouse carcinoembryonic antigen related cell adhesion molecule 1a (mCEACAM1a) as the receptor20, and the receptors for SARS-CoV and MERS-CoV are human angiotensin-converting enzyme 2 (hACE2)21 and human dipeptidyl peptidase 4 (hDPP4)22, respectively. While S proteins of SARS-CoV-2 share about 76% and 97% of amino acid identities with SARS-CoV and RaTG13, respectively, the amino acid sequence of potential RBD of SARS-CoV-2 is only about 74% and 90.1% homologous to that of SARS-CoV and RaTG13, respectively. Recently, Zhou et al.13 reported that SARS-CoV-2 uses hACE2 as the receptor.
Fig. 1 Incorporation of SARS-CoV-2 S protein into pseudovirions.
a Diagram of full-length SARS-CoV-2 S protein with a 3xFLAG tag. S1, receptor-binding subunit; S2, membrane fusion subunit; TM, transmembrane domain; NTD, N-terminal domain; pFP, potential fusion peptide; HR-N, heptad repeat-N; HR-C, heptad repeat-C; b–f Detection of CoVs S protein in cells lysate by western blot. Mock, 293T cells transfected with empty vector. b Mouse monoclonal anti-FLAG M2 antibody; c Polyclonal goat anti-MHV-A59 S protein antibody AO4. d Polyclonal rabbit anti-SARS S1 antibodies T62. e Mouse monoclonal anti-SARS S1 antibody. f Mouse monoclonal anti-MERS-CoV S2 antibody. g–j Detection of CoVs S protein in pseudovirions by western blot.Gag-p24 served as a loading control. g Anti-FLAG M2. h Polyclonal goat anti-MHV-A59 S protein antibody AO4. i Polyclonal rabbit anti-SARS S1 antibodies T62. j Polyclonal anti-Gag-p24 antibodies. uncleaved S protein, about 180 kDa; cleaved S protein, about 90 kDa. Experiments were done twice and one is shown. Source data are provided as a Source Data file.