Molecular evolution and adaptation of SARS-CoV-2 omicron XBB sub-lineage Spike protein under African selection pressure

Abstract The SARS-CoV-2 Omicron variant of concern (VOC) has multiple mutations in the spike (S) protein, which mediates viral infection and immunity. We analysed a sub-lineage of Omicron, designated XBB, that showed structural and functional changes in the S protein in response to the African selection pressures. We used molecular modelling to compare the S protein structures of Omicron and XBB and found that XBB had a reduced receptor-binding domain (RBD) due to the loss of some β-sheets, which may increase its affinity to the human angiotensin-converting enzyme 2 (hACE2) receptor. We also used Fast Unconstrained Bayesian AppRoximation (FUBAR) and Recombination Detection Program 4 (RDP 4) to perform selection and recombination analysis of the S protein sequences of Omicron and XBB and detected signals of positive selection and recombination in the N-terminal domain (NTD) of the S1 subunit, which contains antibody-binding epitopes, and the RBD, which is involved in viral entry. Our results reveal the structural and functional adaptation of the Omicron XBB variant in Africa and its potential implications for viral pathogenesis and immunity.