Role of gp41 glycosylation sites in the biological activity of human immunodeficiency virus type 1 envelope glycoprotein.

The requirement for glycosylation in the transmembrane protein, gp41, of human immunodeficiency virus type 1 envelope protein for fusion activity has been studied. By using a mutant gene in which three conserved sites have been removed and which shows no fusion ability, genes were constructed which replace one, two, or three sites in all possible combinations. Following expression of the resultant proteins using the vaccinia T7 system, each Env variant was assessed by visual and quantitative syncytium assays. Our data indicate that two sites are sufficient for high levels of fusion and that the single site at position 621 is the most critical of all positions. We interpret our data in the light of previous contradictory reports on the role of gp41 glycosylation in bioactivity and the emerging structure of gp41.