Glycosylation and processing of the human immunodeficiency virus type 1 envelope protein.

The human immunodeficiency virus type 1 (HIV-1) envelope protein is synthesized as a gp160 precursor that is cleaved to a 120 kDa exterior glycoprotein (gp120) and a 41 kDa transmembrane glycoprotein (gp41). The HIV-1 envelope protein was stably expressed under the control of the transactivator proteins tat and rev, in wild-type and mutant Chinese hamster ovary (CHO) cells. The mutant, ldlD, is conditionally defective for the addition of galactose and N-acetylgalactosamine to oligosaccharide chains. The effects of glycosylation modification on the HIV-1 envelope's structure and function were examined. The effects of galactosylation on the structure of the envelope proteins suggest that cleavage of the gp160 precursor into gp120 and gp41 occurs intracellularly, apparently concurrent with the addition of galactose to N-linked oligosaccharides of the envelope proteins. No evidence for O-linked glycosylation of the envelope proteins in CHO cells was observed. The envelope protein in the transfected hamster cells mediated the fusion of these cells with CD4-positive lymphocytes, and this fusogenic activity was independent of the addition of either galactose or N-acetylgalactosamine to oligosaccharides in the transfected cells.