The hemagglutinin (HA) of A/H3N2 pandemic influenza viruses (IAVs) of 1968 differed from its inferred avian precursor by eight amino acid substitutions. To determine their phenotypic effects, we studied recombinant variants of A/Hong Kong/1/1968 virus containing either human-type or avian-type amino acids in the corresponding positions of HA. The precursor HA displayed receptor binding profile and high conformational stability typical for duck IAVs. Substitutions Q226L and G228S, in addition to their known effects on receptor specificity and replication, marginally decreased HA stability. Substitutions R62I, D63N, D81N and N193S reduced HA binding avidity. Substitutions R62I, D81N and A144G promoted viral replication in human airway epithelial cultures. Analysis of HA sequences revealed that substitutions D63N and D81N accompanied by the addition of N-glycans represent common markers of avian H3 HA adaptation to mammals. Our results advance understanding of genotypic and phenotypic changes in IAV HA required for avian-to-human adaptation and pandemic emergence.
Bibliographical noteFunding Information:
This work was supported by the European Union's Seventh Framework Programme for Research, Technological Development, and Demonstration under grant agreement 278433 - PREDEMICS (Mikhail Matrosovich); by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Project numbers 197785619 - SFB 1021 (Mikhail Matrosovich) and 284237345 - KF0309/Z1 (Jochen Wilhelm); by an NWO VIDI grant (contract number 91715372) (Sander Herfst); and by NIH/NIAID contract HHSN272201400008C (Ron Fouchier). Johanna West was supported by a fellowship from the J?rgen Manchot Stiftung, D?sseldorf, Germany. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
© 2021 West et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.