Processing of the glycoprotein of feline immunodeficiency virus: effect of inhibitors of glycosylation.

The processing and transport of the envelope glycoprotein complex of feline immunodeficiency virus (FIV) in the persistently infected Crandell feline kidney (CRFK) cell line were investigated. Pulse-chase analyses revealed that the glycoprotein is synthesized as a precursor with an Mr of 145,000 (gp145) and is quickly trimmed to a molecule with an Mr of 130,000 (gp130). Treatment of gp130 with endoglycosidase H (endo H) resulted in a protein with an Mr of 75,000, indicating that nearly half the weight of the gp130 precursor consists of endo H-sensitive glycans during biosynthesis. Chase periods of up to 8 h revealed intermediates during the further processing of this glycoprotein precursor. Initially, two minor protein species with apparent Mrs of 100,000 and 90,000 were detected along with gp130. At later chase times these two species appeared to migrate as a single dominant species with an Mr of 95,000 (gp95). Concomitant with the appearance of gp95 was another protein with an Mr of approximately 40,000 (gp40). Chase periods of up to 8 h revealed that approximately half of the precursor was processed into the gp95-gp40 complex within 4 h. gp95 was efficiently transported from the cell into the culture medium by 1 to 2 h after labeling, whereas gp40 was not observed to be released from infected CRFK cells. Analysis of the processing in the presence of monensin, castanospermine, and swainsonine also suggests the existence of these intermediates in the processing of this lentivirus glycoprotein. As with human immunodeficiency virus, virus produced in the presence of glucosidase inhibitors and reduced infectivity for T-lymphocyte cultures.