Structural basis for the enhanced infectivity and immune evasion of Omicron subvariants

Abstract

The Omicron variants of SARS-CoV-2 have recently become the globally dominant variants of concern in the COVID-19 pandemic. At least five major Omicron sub-lineages have been characterized: BA.1, BA.2, BA.3, BA.4 and BA.5. They all possess over 30 mutations on the Spike (S) protein. Here we report the cryo-EM structures of the trimeric S proteins from the five subvariants, of which BA.4 and BA.5 share the same mutations of S protein, each in complex with the surface receptor ACE2. All three receptor binding domains of S protein from BA.2 and BA.4/BA.5 are "up", while the BA.1 S protein has two "up" and one "down". The BA.3 S protein displays increased heterogeneity, with the majority in the all "up" RBD state. The differentially preferred conformations of the S protein are consistent with their varied transmissibilities. Analysis of the well defined S309 and S2K146 epitopes reveals the underlie immune evasion mechanism of Omicron subvariants.