Abstract
The recently emerged B.1.1.529 (Omicron) severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant has a highly divergent spike (S) glycoprotein. We compared the functional properties of B.1.1.529 BA.1 S with those of previous globally prevalent SARS-CoV-2 variants, D614G and B.1.617.2. Relative to these variants, B.1.1.529 S exhibits decreases in processing, syncytium formation, virion incorporation, and ability to mediate infection of cells with high TMPRSS2 expression. B.1.1.529 and B.1.617.2 S glycoproteins bind ACE2 with higher affinity than D614G S. The unliganded B.1.1.529 S trimer is less stable at low temperatures than the other SARS-CoV-2 Ss, a property related to its more "open" S conformation. Upon ACE2 binding, the B.1.1.529 S trimer sheds S1 at 37°C, but not at 0°C. B.1.1.529 pseudoviruses are relatively resistant to neutralization by sera from patients with coronavirus disease 2019 (COVID-19) and vaccinees. These properties of the B.1.1.529 S glycoprotein likely influence the transmission, cytopathic effects, and immune evasion of this emerging variant.