A single amino acid change switches avian influenza H5N1 and H7N9 viruses to human receptors

Two back-to-back papers were published last week that provide a detailed analysis of what it would take for avian influenza H5N1 and H7N9 viruses to switch to human receptors. Influenza virus initiates infection by attaching to the cell surface, a process mediated by binding of the viral hemagglutinin protein (HA) to sialic acid. This sugar is found on glycoproteins, which are polypeptide chains decorated with chains of sugars. The way that sialic acid is linked to the next sugar molecule determines what kind of influenza viruses will bind. Human influenza viruses prefer to attach to sialic acids linked to the second sugar molecule via alpha-2,6 linkages, while avian influenza viruses prefer to bind to alpha-2,3 linked sialic acids. (In the image, influenza HA is shown in blue on the virion (left) and as a single polypeptide at right. Alpha-2,3 linked sialic acid is shown at top). Adaptation of avian influenza viruses to efficiently infect humans requires that the viral HA quantitatively switches to human receptor binding –  defined as high relative binding affinity to human versus avian receptors. Such a switch is caused by amino acid changes in the receptor binding site of the HA protein. The HA of the H1N1, H2N2, and H3N2 pandemic viruses are all derived from avian influenza viruses that underwent such a quantitative switch in binding from avian to human sialic acid receptors. Avian H5N1 influenza viruses have not undergone a quantitative switch to human receptor bi...
Source: virology blog - Category: Virology Authors: Tags: Basic virology Information avian influenza evolution H5N1 h7n9 mutation pandemic receptor binding site sialic acid viral virus Source Type: blogs