In new study led by @timyu.bsky.social, we measure how mutations to H3 flu HA affect cell entry, stability & antibody escape We find pleiotropic effects of mutations on these phenotypes shape evolution: epistasis alleviates cell-entry but not stability constraints biorxiv.org
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We used pseudovirus deep mutational scanning to characterize all mutations to a recent H3N2 HA. This approach uses virions that can only undergo one round of cell entry & so are not pathogens capable of causing disease. All measurements available here: dms-vep.org
dms-vep.org
As can be seen below, constraint due to mutational impacts on cell entry are widely distributed across HA including receptor-binding pocket and fusion peptide. But mutational constraint due to HA stability is concentrated at trimer and HA1-HA2 interface.
We then looked for evidence of epistasis by examining whether mutations had become entrenched. A mutation is entrenched if reverting it to the ancestral amino acid is deleterious in recent HAs, as schematized below.
We found extensive entrenchment w respect to cell entry in receptor binding pocket (see below), consistent w prior work by @wchnicholas.bsky.social @rpdevrieslab.bsky.social nature.com biorxiv.org But there was minimal entrenchment w respect to HA stability
To examine implications for antigenic evolution, we measured how all HA mutations affected serum antibody neutralization. Mutations at key trimer interface sites that cause substantial antibody escape but destabilize HA have never fixed.
Overall, these results show how pleiotropic effects of mutations constrain HA evolution. Epistasis can alleviate these constraints w respect to cell entry in receptor binding pocket, but we find no evidence that mutations that strongly destabilize HA ever fix in H3N2 evolution. All the data are available for visualization and download at dms-vep.org Thanks to @timyu.bsky.social for leading study, and also @ckikawa.bsky.social, @bdadonaite.bsky.social, Andrea Loes, & Jane Englund.
dms-vep.org
The final version of this article has been published in @natecoevo.nature.com alongside a nice News and Views by @seth-zost.bsky.social: nature.com
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