Phylogenetically important regions of the influenza A H1 hemagglutinin protein.

A parsimony approach was used to construct phylogenetic trees of the H1, H2 and H3 influenza hemagglutinin subtypes. The parsimony trees were then compared with randomly generated trees to identify regions of the proteins containing the most phylogenetic information, i.e. those regions making the parsimony trees shorter. We reasoned that any areas of the hemagglutinin protein that were phylogenetically 'information-rich' would be good candidates for sites involved in virus-host interactions and their identification might lead to a better understanding of the protein. Molecular modelling, based upon the crystal structure of the H3 hemagglutinin, demonstrated that most phylogenetically important regions of the H1 subtype were on the surface of the hemagglutinin trimer, primarily in the globular region. Many corresponded to known antigenic or receptor binding sites, while others appear to be novel and specific for H1.