Selective retention of monoglucosylated high mannose oligosaccharides by a class of mutant vesicular stomatitis virus G proteins.
Cells infected with a temperature-sensitive mutant of vesicular stomatitis virus, ts045, or transfected with the plasmid vector pdTM12 produce mutant forms of the G protein that remain within the ER. The mutant G proteins were isolated by immunoprecipitation from cells metabolically labeled with [2-3H]mannose to facilitate analysis of the protein-linked oligosaccharides. The 3H-labeled glycopeptides recovered from the immunoprecipitated G proteins contained high mannose-type oligosaccharides. Structural analysis, however, indicated that 60-78% of the 3H-mannose-labeled oligosaccharides contained a single glucose residue and no fewer than eight mannose residues. The 3H-labeled ts045 oligosaccharides were deglucosylated and processed to complex-type units after the infected cells were returned to the permissive temperature. When shifted to the permissive temperature in the presence of a proton ionophore, the G protein oligosaccharides were deglucosylated but remained as high mannose-type units. The glucosylated state was observed, therefore, when the G protein existed in an altered conformation. The ts045 G protein oligosaccharides were deglucosylated in vitro by glucosidase II at both the permissive and nonpermissive temperatures. G protein isolated from ts045-infected cells labeled with [6-3H]galactose in the presence of cycloheximide contained 3H-glucose-labeled monoglucosylated oligosaccharides, indicating that the high mannose oligosaccharides were glucosylated in a posttranslational process. These results suggest that aberrant G proteins are selectively modified by resident ER enzymes to retain monoglucosylated oligosaccharides.
Suh
K
K
Department of Anatomy and Cell Biology, College of Physicians and Surgeons, Columbia University, New York 10032.
Bergmann
J E
JE
Gabel
C A
CA
D000818:Animals; D002460:Cell Line; D005947:Glucose / Q000378:metabolism*; D008358:Mannose / Q000032:analysis; D008562:Membrane Glycoproteins; D009154:Mutation; D009844:Oligosaccharides / Q000032:analysis / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D013696:Temperature; D014162:Transfection; D014721:Vesicular stomatitis Indiana virus / Q000235:genetics; D014759:Viral Envelope Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*
C028391:G protein, vesicular stomatitis virus; D008562:Membrane Glycoproteins; D009844:Oligosaccharides; D014759:Viral Envelope Proteins; D005947:Glucose; D008358:Mannose