THE GLYCOSYLATION OF THE INFLUENZA-A VIRUS HEMAGGLUTININ BY MAMMALIAN-CELLS - A SITE-SPECIFIC STUDY

We have characterized the glycans at individual sites on the hemagglut inin of three influenza A variants to obtain information on the role o f cell-specific glycosylation in determining the receptor binding prop erties of this virus, The variants differ in whether they have a glyco sylation site at residue 129 on the tip of the hemagglutinin and wheth er amino acid 184 (near to the receptor binding site) is His or Asn. W e found that all sites on each variant are glycosylated in Madin-Darby bovine kidney cells, that the glycosylation is site-specific, and tha t the glycans at the same site in each variant are highly similar. One site that is buried in the hemagglutinin trimer contains only oligoma nnose glycans, The remaining sites carry complex glycans of increasing size as the distance of the site from the viral membrane decreases, M ost of these complex glycans are terminated with alpha-galactose resid ues, a consequence in bovine cells of the removal of terminal sialic a cids by the viral neuraminidase, Although the glycans at residue 129 a re among the smallest on the molecule, they are large enough to reach the receptor binding pocket on their own and adjacent monomers. The re sults suggest that the reduction in receptor binding observed with Mad in-Darby bovine kidney cell-grown virus is due to the combined effect of large complex glycans at the tip of the hemagglutinin and a His to Asn substitution close to the receptor binding pocket.