Assessing flu's pandemic potential

H5N1's sugar preference may help health officials assess whether a given strain of the infamous avian influenza virus has the potential to start a human pandemic. A group of 23 international researchers led by Yoshihiro Kawaoka of both the University of Tokyo and the University of Wisconsin, Madison, pinpointed mutations in an H5N1 protein that switch the virus's ability to infect avian or human hosts (Nature 2006, 444, 378). This change of appetite occurs in a viral protein called hemagglutinin, whose binding to sugars located on bird or human host receptor proteins leads to infection. Avian H5N1 hemagglutinin has a predilection for bird protein receptors laced with sialic acid-α2,3-galactose. Human H5N1 hemagglutinin prefers sialic acid-α2,6-galactose, common to human receptor proteins. The researchers identified several amino acids in the hemagglutinin's binding cleft that help switch a virus that goes after birds to one that targets humans. Those residues could be useful when assessing the pandemic potential of H5N1 samples.