Glycosylation is not required for the fusion activity of the G protein of vesicular stomatitis virus in insect cells

The gene encoding the complete glycoprotein of vesicular stomatitis virus (VSV, Indiana serotype G protein) with potential asparagine-linked glycans at amino acid residues 179 and 338 was inserted into a baculovirus transfer vector pAcYM1, derived from the nuclear polyhedrosis virus of Autographa californica (AcNPV). The gene was placed under the control of the AcNPV polyhedrin promotor and expressed by the derived recombinant viruses to high levels in Spodoptera frugiperda cell lines. The principal product was the glycosylated version of the G protein, although some alternative (including probable degradation) forms of the protein were also observed. Similar recombinant viruses were prepared with deletion of one, the other, or both glycosylation sites of the VSV G protein. All forms expressed VSV G protein derivatives and mediated cell fusion and the production of syncytia at low pH. The fusogenic properties of the VSV G protein expressed on the surface of insect cells was prevented using anti-VSV sera, or by elevating the pH above 6.2. A reduction of the pH to 5.5, or 5.0, accelerated the rate of syncytia formation.