Preferential Recognition of Avian-Like Receptors in Human Influenza A H7N9 Viruses

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Science  06 Dec 2013:
Vol. 342, Issue 6163, pp. 1230-1235
DOI: 10.1126/science.1243761

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Avian Affinity for H7N9

Structural analyses of the binding of avian origin H7N9 influenza viruses have revealed how the receptor-binding characteristics differentiate between birds and mammals, and studies involving the use of whole viruses have suggested that the virus is acquiring human-type receptor specificity. In contrast, Xu et al. (p. 1230) show that the H7 hemagglutinin strongly retains its specificity for avian-type receptors by using cocrystal structures with receptor analogs and glycan binding analysis with recombinant hemagglutinin against a library of receptor analogs. Thus, current human H7N9 viruses appear to remain poorly adapted to human receptors, and additional mutations will be required to achieve specificity for human-type receptors equivalent to those of human pandemic viruses.


The 2013 outbreak of avian-origin H7N9 influenza in eastern China has raised concerns about its ability to transmit in the human population. The hemagglutinin glycoprotein of most human H7N9 viruses carries Leu226, a residue linked to adaptation of H2N2 and H3N2 pandemic viruses to human receptors. However, glycan array analysis of the H7 hemagglutinin reveals negligible binding to humanlike α2-6–linked receptors and strong preference for a subset of avian-like α2-3–linked glycans recognized by all avian H7 viruses. Crystal structures of H7N9 hemagglutinin and six hemagglutinin-glycan complexes have elucidated the structural basis for preferential recognition of avian-like receptors. These findings suggest that the current human H7N9 viruses are poorly adapted for efficient human-to-human transmission.

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