Compensatory evolution of net-charge in influenza A virus hemagglutinin.
The propagation of influenza A virus depends on the balance between the activities of hemagglutinin (HA) for binding to host cells and neuraminidase (NA) for releasing from infected cells (HA-NA balance). Since the host cell membrane and the sialic acid receptor are negatively charged, the amino acid substitutions increasing (charge+) and decreasing (charge-) the positive charge of HA subunit 1 (HA1) enhance and reduce, respectively, the binding avidity and affinity. The positive charge of HA1 in human influenza A virus bearing subtype H3N2 (A/H3N2 virus) was observed to have increased during evolution, but the evolutionary mechanism for this observation was unclear because this may disrupt the HA-NA balance. Here we show, from the phylogenetic analysis of HA for human A/H3N2 and A/H1N1 viruses, that the relative frequencies of charge+ and charge- substitutions were elevated on the branches where the number of N-glycosylation sites (NGS) increased and decreased, respectively, compared to those where the number of NGS did not change. On the latter branches, the net-charge of HA1 appeared to have been largely maintained to preserve its structure and function. Since the charge+ and charge- substitutions in HA1 have opposite effects to the gain and loss of NGS on the binding and release of the virus, the net-charge of HA1 may have evolved to compensate for the effect of the gain and loss of NGS, probably through changing the avidity. Apparently, the relative frequency of charge- substitutions in HA1 of A/H3N2 virus was elevated after the introduction of oseltamivir, and that of charge+ substitutions in HA1 of A/H1N1 virus was elevated after the spread of oseltamivir resistance. These observations may also be explained by the compensatory effect of the net-charge in HA1 on the NA activity for keeping the HA-NA balance.
Graduate School of Natural Sciences, Nagoya City University, Nagoya City, Aichi, Japan.
Yuki
Y
Kobayashi
Yoshiyuki
Y
Suzuki
D019943:Amino Acid Substitution / Q000235:genetics; D001665:Binding Sites; D019143:Evolution, Molecular; D006031:Glycosylation / Q000187:drug effects; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry* / Q000235:genetics*; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics; D053122:Influenza A Virus, H3N2 Subtype / Q000187:drug effects / Q000235:genetics; D009980:Influenza A virus / Q000187:drug effects / Q000235:genetics*; D053139:Oseltamivir / Q000494:pharmacology; D010802:Phylogeny; D011991:Receptors, Virus / Q000378:metabolism; D013997:Time Factors
D019267:Hemagglutinin Glycoproteins, Influenza Virus; D011991:Receptors, Virus; D053139:Oseltamivir