Selection analysis identifies clusters of unusual mutational changes in Omicron lineage BA.1 that likely impact Spike function.
journal contributionposted on 2022-04-21, 10:57 authored by Darren P Martin, Spyros Lytras, Alexander G Lucaci, Wolfgang Maier, Björn Grüning, Stephen D Shank, Steven Weaver, Oscar A MacLean, Richard J Orton, Philippe Lemey, Maciej F Boni, Houriiyah Tegally, Gordon W Harkins, Cathrine Scheepers, Jinal N Bhiman, Josie Everatt, Daniel G Amoako, James Emmanuel San, Jennifer Giandhari, Alex Sigal, NGS-SA, Carolyn Williamson, Nei-Yuan Hsiao, Anne von Gottberg, Arne De Klerk, Robert W Shafer, David L Robertson, Robert J Wilkinson, B Trevor Sewell, Richard Lessells, Anton Nekrutenko, Allison J Greaney, Tyler N Starr, Jesse D Bloom, Ben Murrell, Eduan Wilkinson, Ravindra K Gupta, Tulio de Oliveira, Sergei L Kosakovsky Pond
Among the 30 non-synonymous nucleotide substitutions in the Omicron S-gene are 13 that have only rarely been seen in other SARS-CoV-2 sequences. These mutations cluster within three functionally important regions of the S-gene at sites that will likely impact (i) interactions between subunits of the Spike trimer and the predisposition of subunits to shift from down to up configurations, (ii) interactions of Spike with ACE2 receptors, and (iii) the priming of Spike for membrane fusion. We show here that, based on both the rarity of these 13 mutations in intrapatient sequencing reads and patterns of selection at the codon sites where the mutations occur in SARS-CoV-2 and related sarbecoviruses, prior to the emergence of Omicron the mutations would have been predicted to decrease the fitness of any virus within which they occurred. We further propose that the mutations in each of the three clusters therefore cooperatively interact to both mitigate their individual fitness costs, and, in combination with other mutations, adaptively alter the function of Spike. Given the evident epidemic growth advantages of Omicron over all previously known SARS-CoV-2 lineages, it is crucial to determine both how such complex and highly adaptive mutation constellations were assembled within the Omicron S-gene, and why, despite unprecedented global genomic surveillance efforts, the early stages of this assembly process went completely undetected.