Avian and human receptor binding by hemagglutinins of influenza A viruses.

An understanding of the structural determinants and molecular mechanisms involved in influenza A virus binding to human cell receptors is central to the identification of viruses that pose a pandemic threat. To date, only a limited number of viruses are known to have infected humans even sporadically, and this has recently included the virulent H5 and H7 avian viruses. We compare here the 3-dimensional structures of H5 and H7 hemagglutinins (HA) complexed with avian and human receptor analogues, to highlight regions within the receptor binding domains of these HAs that might prevent strong binding to the human receptor.