THE HEMAGGLUTININS OF DUCK AND HUMAN H1 INFLUENZA-VIRUSES DIFFER IN SEQUENCE CONSERVATION AND IN GLYCOSYLATION

We determined the deduced amino acid sequences of two H1 duck influenz a A virus hemagglutinins (HAs) and found that the consensus sequence o f the HA, determined directly from virus recovered from the intestinal tract, remains unchanged through many generations of growth in MDCK c ells and chicken embryos. These two duck viruses differ from each othe r by 5 amino acids and from A/Dk/Alberta/35/1976 (F. J. Austin, Y. Kaw aoka, and R. G. Webster, J. Gen. Virol. 71:2471-2474, 1990) by 9 and 1 2 amino acids, most of which are in the HA1 subunit. They are antigeni cally similar to each other but different from the Alberta virus. We c ompared these H1 duck HAs with the HAs of human isolates to identify s tructural properties of this viral glycoprotein that are associated wi th host range. By comparison to the human H1 HAs, the duck virus RA se quences are highly conserved as judged by the small fraction of nucleo tide differences between strains which result in amino acid substituti ons. However, the most striking difference between these duck and huma n HAs is in the number and distribution of glycosylation sites. Wherea s duck and swine viruses have four and five conserved glycosylation, s ites per HA1 subunit, none of which are on the tip of the HA, all huma n viruses have at least four additional sites, two or more of which ar e on the tip of the HA. These findings stress the role of glycosylatio n in the control of host range and suggest that oligosaccharides on th e tip of the RA are important to the survival of H1 viruses in humans hut not in ducks or swine.