Cloning and expression of the HN gene from the velogenic viscerotropic Newcastle disease virus strain AF2240 in Sf9 insect cells.

The haemagglutinin-neuraminidase (HN) gene ofNewcastle disease virus (NDV) strain AF2240, amplifiedfrom the viral genomic RNA ( approximately 1.8 kb) was directionallycloned and inserted into a baculovirus expressionvector system. The recombinant glycoprotein expressedin Spodoptera frugiperda (Sf9) cellsshowed haemagglutinin (HA), neuraminidase (NA) andhemadsorption activities. HA activity was detected inboth extra- and intra-cellular recombinant HN(recHNAF2240) samples. In addition, both HA andhemadsorption activities were inhibited by polyclonalanti-NDV sera. Furthermore, significant expression ofthe recombinant protein was observed on the surface ofinfected cells. SDS-PAGE analysis revealed thepresence of visually distinguishable bands between the70 and 80 kDa in size that were absent in thewild-type samples. Western blot analysis showed thatthe distinct approximately 63 kDa band and a approximately 75 kDa bandcorresponded to the unglycosylated and glycosylated HNglycoprotein respectively as reported in anotherstudy. These observations indicated that the HNrecombinant protein was not only expressed on thesurface of the infected cells as well as with theviral coat protein, but also appears to be functional.