Effect of Amino Acid Substitutions on Glycosylation of the Haemagglutinin-Neuraminidase Glycoprotein of Newcastle Disease Virus

The nucleotide sequences of two monoclonal antibody-resistant mutant viruses predict changes from the wild-type in the number of potential glycosylation sites (Asn-X-Thr/Ser) in the mutant haemagglutinin-neuraminidase (HN) glycoproteins of the Beaudette C strain of Newcastle disease virus. The HN glycoproteins ofthese mutants, F5 and Z18, migrate either slower (F5) or faster (Z18) than that of the wild-type in SDS-PAGE. HN proteins ynthesized in chick embryo fibroblasts following infection by either mutant or wild-type virus in the presence of tunicamycin (an inhibitor of glycosylation), comigrate on SDS-PAGE. These results confirm that the HN protein of the mutant virus, F5, has gained a glycosylation site at Asn(323)-Ser-Ser and that the conserved potential glycosylation site at Asn(481)-His-Thr is indeed glycosylated in the HN protein of the wild-type Beaudette C strain of Newcastle disease virus but is lost in that of the mutant virus, Z18. Three antigenic sites on the haemagglutinin-neuraminidase (HN) glycoprotein of the Newcastle disease virus (NDV) strain Beaudette C have recently been identified on the basis of competitive binding assay experiments u ing anti-HN monoclonal antibodies (MAbs). Direc