Effect of N-linked glycosylation at position 162 of hemagglutinin in influenza A virus A(H1N1)pdm09

Subtype H1N1 influenza A virus (IAV) that caused a pandemic in 2009, called A(H1N1)pdm09, has been circulating as a seasonal IAV among humans, escaping from herd immunity through amino acid substitutions in hemagglutinin (HA). Additionally, position 162 of HA in A(H1N1)pdm09 evolved to be N-linked glycosylated by 2017. Here the effect of N-linked glycosylation at position 162 of HA in A(H1N1)pdm09 was examined by comparing the ratio of nonsynonymous diversity (πN) to synonymous diversity (πS) (πN/πS) at structurally defined categories of amino acid sites between 1785 (162+) and 7562 (162−) sequences of HA that were and were not considered to be N-linked glycosylated at position 162, respectively. In 162− sequences, πN/πS for the sites located inside 15 Å from position 162 was not significantly smaller than one and was greater than that for the sites located outside 15 Å. In 162+ sequences, πN/πS for the sites located inside and outside 15 Å from position 162 were smaller than the corresponding values in 162− sequences, and were not significantly different from each other. These results suggest that N-linked glycosylation at position 162 of HA may shield epitopes against antibodies in A(H1N1)pdm09.