SARS-CoV-2(26) COVID-19(18) the SARS-CoV-2(14) mechanism(14) RdRP(11) RNA(11) RNA-dependent RNA polymerase(11) complex(11) COVID-19 pandemic(10) Mutation(10) Treatment(10) antibody(9) epitope(9) Protein(8) trimer(8) cause(8) RBD(8) ectodomain(8) prefusion(8) reveal(8) Receptor binding(8) analysis(8) Analysis(7) ACE2(7) Infection(7) conserved(7) Cryoelectron microscopy(7) the spike protein(7) receptor(7) cryo-EM(6)