Interaction between HR1 and HR2 of SARS-CoV-2 and SARS-CoV.a-d. The 6-HB structure of SARS-CoV-2 and SARS-CoV is shown in cartoon representation. The HR1 domain is shown in green for SARS-CoV-2 and forest for SARS-CoV, while the HR2 domain is shown in cyan for SARS-CoV-2 and orange for SARS-CoV. Important residues are shown in sticks and labeled. 