Fig. 2.

Schematic illustration of four structures of antigenic proteins of coronavirus, nucleic acid and protein sequence of SARS-CoV-2 spike protein (red area), and main residues in the spike protein that bonding to the ACE2 receptor (blue area) (Andersen et al., 2020). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)