b. Structure of SARS-CoV-2 6-HB is shown in cartoon representation with HR1 colored in green and HR2 in cyan. The structural dimensions are indicated in angstroms. c. HR1 trimer of SARS-CoV-2 6-HB is shown in electrostatic surface, and HR2 domain is shown in cartoon representation, the important binding residues of which are shown in sticks and labeled. d. The superposition of 6-HB structure of SARS-CoV (PDB entry 1WYY), MERS-CoV (PDB entry 4NJL) and SARS-CoV-2 is shown in ribbon. The RMSD between structures is indicated. e. The sequence comparison of 6-HB structure of different HCoVs is shown in cartoon representation with different colors for HR1 and HR2. The helical fusion core regions are indicated. 