ROLE OF N-LINKED OLIGOSACCHARIDE CHAINS IN THE PROCESSING AND ANTIGENICITY OF MEASLES-VIRUS HEMAGGLUTININ PROTEIN

The effects of N-linked oligosaccharides on the haemagglutinin (H) pro tein of measles virus (MV) were assessed with respect to the processin g and antigenicity of the molecule. The functional glycosylation sites on the H protein were determined by eliminating each of the five pote ntial positions, Asn-168, Asn-187, Asn-200, Asn-215 and Asn-238, for N -linked glycosylation by oligonucleotide-directed mutagenesis on a cDN A clone. Expression of the mutant H proteins in BHK-21 cells by a reco mbinant vaccinia virus encoding T7 polymerase indicated that the first four sites were used in the H glycoprotein for the addition of N-link ed oligosaccharide chains. Heterogeneity of oligosaccharide processing was demonstrated. One of the four glycosylation sites had a different carbohydrate structure from those of the other three glycosylation si tes and this varied glycosylation was responsible for the appearance o f two forms of the H protein. The functional glycosylation sites were systematically removed in various combinations from the H protein to f orm a panel of mutants in which the role of carbohydrate chains, singl y or in different combinations, could be evaluated. Investigations of these glycosylation mutants indicated that (i) two of the four individ ual carbohydrate side-chains have a large influence on the antigenicit y of the molecule; (ii) individual carbohydrate side-chains have littl e effect on the folding and oligomerization of the molecule, and are n ot sufficient or necessary alone to facilitate the transport of the mo lecule to the plasma membrane; (iii) at least two carbohydrate side-ch ains are required for the H protein to move along the exocytic pathway to the plasma membrane and various combinations of oligosaccharide si de-chains, irrespective of the carbohydrate localizations, influence e qually the processing of the molecule.