Random forest algorithm reveals novel sites in HA protein that shift receptor binding preference of the H9N2 avian influenza virus

A switch from avian-type α-2,3 to human-type α-2,6 receptors is an essential element for the initiation of a pandemic from an avian influenza virus. Some H9N2 viruses exhibit a preference for binding to human-type α-2,6 receptors. This identifies their potential threat to public health. However, our understanding of the molecular basis for the switch of receptor preference is still limited. In this study, we employed the random forest algorithm to identify the potentially key amino acid sites within hemagglutinin (HA), which are associated with the receptor binding ability of H9N2 avian influenza virus (AIV). Subsequently, these sites were further verified by receptor binding assays. A total of 12 substitutions in the HA protein (N158D, N158S, A160 ​N, A160D, A160T, T163I, T163V, V190T, V190A, D193 ​N, D193G, and N231D) were predicted to prefer binding to α-2,6 receptors. Except for the V190T substitution, the other substitutions were demonstrated to display an affinity for preferential binding to α-2,6 receptors by receptor binding assays. Especially, the A160T substitution caused a significant upregulation of immune-response genes and an increased mortality rate in mice. Our findings provide novel insights into understanding the genetic basis of receptor preference of the H9N2 AIV.