The novel SARS-coronavirus 2 (SARS-CoV-2) which causes the disease COVID-19 has been shown to utilize the SARS-CoV receptor ACE2 for entry into human cells (Hoffman, M. et al., Cell 2020). The entry of a coronavirus into host cells is mediated by the viral surface-anchored transmembrane spike (S) glycoprotein which is composed of two functional subunits, S1 which binds the receptor and S2 which fuses the membrane (Walls, AC et.al., Cell 2020). S1 contains a receptor-binding domain (RBD) which specifically recognizes ACE2 as its receptor (Wan, Y. et al., 2020).
