The cellular receptors of SARS-CoV and MERS-CoV have been identified [25,26], and the virion spike (S) glycoprotein, was also well studied. S glycoprotein includes two subunits [27], S1 and S2, resulting from cleavage of the one precursor into two parts. S1 determines the virus host range and cellular tropism with the key functional domain - receptor binding domain (RBD), while S2 contains two tandem domains, heptad repeats 1 (HR1) and heptad repeats 2 (HR2), to mediate virus-cell membrane fusion. It is believed that the fusion process is similar to that of HIV-1 [28]; for example, when S1 binds to the receptor on the cell membrane, the fusion peptide at the N terminus of S2 inserts into the cell membrane, then three HR1s attach to each other in parallel as a trimer, followed by binding of three HR2s separately onto the outside of the trimer to form a 6-helix bundle, thus bringing virus and cell membranes close to each other to trigger fusion.