Effects of glycosylation on biological activities of hemagglutinin-neuraminidase of newcastle disease virus
To make sure the effect of glycosylation on biological activities of hemagglutinin - neuraminidase of Newcastle disease virus, especially in the promotion of fusion, the site - directed mutagenesis was used to obtain mutants. The expression intensity, receptor recognition, neuraminidase activity, promotion of fusion and immuno-precipitation activity were assayed. The results showed that expression of D198R - HN mutant was 82.6% as compared with wild - type HN and expression of each mutant was, to different extent, decreased while expression of D198R - HN - G2 and D198R - HN - G4 were even more obvious compared with that of D198R - HN. Receptor recognition activities of G1、G2、G3 and G4 mutants of wild - type HN were 47.95%、68.49%、42.67% and 41.10% respectively after mutation; while those of D198R - HN - G1、G3 and G4 mutants were not much changed, only D198R - HN -G2 mutant restored the activity from 10.96% to 32.88%. The neuramidinase activities of wild - type HN G mutants were all lowered, especially G4 mutant was only 9.60% of that of wild - type HN while those of D198R - HN mutants were all increased, especially the D198R - HN - G2 mutant from 0.45% to 7.59%. The activities of promotion of wild type HN in cell fusion were not changed much after mutation; while D198R - HN - G2 mutant restored by 30.90%. When electrophoresis, all G - mutants migrated faster than its wild - type because one glycosylation site was mutated. D198R - HN - G1, D198R - HN - G3 and D198R - HN - G4 mutants showed two fussy bands, but D198R - HN - G2 mutant showed a sharp and narrow band, and even migrated more faster. The results above indicate that glycosylation of protein can affect transport of HN protein from cytoplasm to cell surface; G2 site greatly affects receptor recognition activity. It is supposed that the changes of G2 make phenotype properties around G2 changed, so that the neuraminidase activity and activity of promotion in cell fusion are altered.