Comparison of S protein sequences of coronaviruses. Multiple alignment of full amino acid sequences of S protein from 2019-nCoV (GISAID accession no. EPI_ISL_402124), SARS-CoV (GenBank accession no. AY278489), bat-SL-CoVZC45 (GenBank accession no. MG772933.1), and bat-SL-CoVZXC21 (GenBank accession no. MG772934.1) was performed and displayed with clustalx1.83 and MEGA4 respectively. ‘‘-” represents the unconfirmed amino acid residues, “.” represents the identical amino acid residues. The functional domains were labeled based on the research on SARS-CoV [41]; light blue box was for RBD region; dark blue box for receptor binding motif (RBM); light purple box for HR1; and dark purple box for HR2, respectively. Double underlined regions in HR1 and HR2 are fusion cores, which are critical regions responsible for the formation of stable six-helical bundles between HR1 and HR2.