Fig. 1.

Schematic diagram of SAR-CoV S protein and the recombinant fusion protein RBD-Fc. The S protein consists of S1 and S2 domains. There is a signal peptide (SP) located at the N-terminus of the S protein. The S1 domain contains a receptor-binding domain (RBD). The S2 domain contains a cytoplasm domain (CP), a transmembrane domain (TM), and an ectodomain composed of a putative internal fusion peptide (FP) and heptad repeat 1 and 2 (HR1 and HR2) regions. RBD-Fc consists of RBD and a human IgG-Fc fragment. S1-C9 contains S protein S1 domain and a C9 fragment.