Identification of a novel mechanism for the removal of glucose residues from high mannose-type oligosaccharides.
The role of glucosylated oligosaccharides in the biogenesis of the glycoprotein (G protein) of vesicular stomatitis virus was studied in PhaR2.7, a mouse lymphoma cell line deficient in glucosidase II activity. As expected, the great majority of cell-associated G protein remained glucosylated in PhaR2.7, and the G protein was rapidly deglucosylated in BW5147, the parental cell line. Despite these differences in glucosylation, the rates of G protein trimerization and transport to the cell surface were as rapid and efficient in the PhaR2.7 mutant as in BW5147. Surprisingly, greater than 73% of the oligosaccharides on G proteins recovered from released virions were complex-type units. The efficient processing of the G protein oligosaccharides coincided with the efficient removal of glucose residues from its oligosaccharides. After treatment with deoxynojirimycin, an inhibitor of endoplasmic reticulum (ER) glucosidases I and II, the total percentage of G protein-associated high mannose-type oligosaccharides increased more in the parental cells than in the mutant cells. Furthermore, when the G protein was retained in the ER of PhaR2.7 cells by depletion of the cellular ATP pools with carbonyl cyanide m-chlorophenylhydrazone, its oligosaccharides remained glucosylated. Under identical conditions, BW5147 cells removed the glucose residues from > 90% of the retained G protein's oligosaccharides. Thus, PhaR2.7 cells efficiently remove glucose residues from high mannose-type oligosaccharides of selected proteins using a deoxynojirimycin-insensitive enzyme located in a post-ER compartment. The existence of a second mechanism for the deglucosylation of N-linked oligosaccharides provides evidence for the important role of glucose removal in glycoprotein maturation.
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Department of Anatomy and Cell Biology, Columbia University College of Physicians and Surgeons, New York, New York 10032.
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Bergmann
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D017485:1-Deoxynojirimycin / Q000494:pharmacology; D000818:Animals; D002451:Cell Compartmentation; D016521:Electrophoresis, Gel, Pulsed-Field; D005947:Glucose / Q000378:metabolism*; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D006031:Glycosylation; D007700:Kinetics; D008358:Mannose / Q000737:chemistry; D008562:Membrane Glycoproteins; D051379:Mice; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014721:Vesicular stomatitis Indiana virus / Q000378:metabolism*; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000378:metabolism*; D000520:alpha-Glucosidases / Q000378:metabolism
C028391:G protein, vesicular stomatitis virus; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D009844:Oligosaccharides; D014759:Viral Envelope Proteins; D017485:1-Deoxynojirimycin; C034251:4-nitrophenyl-alpha-glucosidase; D000520:alpha-Glucosidases; D005947:Glucose; D008358:Mannose