PROS1 and COVID-19: From the MD simulations it was found that SARS-CoV-2 has four pairsof essential hydrogenbonds (high occupancy, >80%), while SARS-CoV has three pairs, which indicates the SARS-CoV-2 S protein has relatively more robust binding strategy than SARS-CoVS protein.Four key residues forming essential hydrogen bonds from SARS-CoV-2 are identified, which are potential drug targets for COVID-19 treatments.