Dolichol-dependent synthesis of chitobiosyl proteins and their further mannosylation. A second route for glycosylation of proteins in rat-spleen lymphocytes?
Incubation of whole lymphocytes with UDP-N-acetyl [3H]glucosamine used as the only precursor leads to the formation of dolichyl diphosphate [3H]chitobiose, DolPP-(GlcNAc)2, and dolichyl diphosphate N-acetyl-[3H]glucosamine, DolPP-GlcNAc. Although very few dolichyl diphosphate oligosaccharides are formed, a high level of radioactivity is recovered with proteins and has been characterized, using hydrazinolysis procedure, as [3H]chitobiosyl and N-acetyl[3H]glucosaminyl units. Addition of tunicamycin inhibits, to the same extent, both the synthesis of DolPP-(GlcNAc)1-2 and the incorporation of the N-acetyl[3H] glucosaminyl residues onto proteins, indicating that these carbohydrate units are transferred onto proteins acceptors from their dolichol derivatives. Chase experiments have indicated that, in fact, the DolPP-(GlcNAc)1-2 were utilized in two ways: either their transfer onto proteins or their degradation into water-soluble saccharidic material. Moreover, the transfer reaction appears to be a slow process compared to the degradation since the radioactivity chased from the DolPP-(GlcNAc)1-2 is not recovered on proteins. This fact allows to show that part of the [3H]chitobiose previously bound to proteins is further converted into oligomannosidic glycans in the presence of GDP-mannose. This direct mannosylation of chitobiosyl-proteins may represent a second route for the N-glycosylation of proteins.
D000818:Animals; D004187:Disaccharides; D004224:Diterpenes / Q000378:metabolism*; D004286:Dolichols / Q000378:metabolism*; D005936:Glucans / Q000378:metabolism*; D006023:Glycoproteins / Q000096:biosynthesis* / Q000378:metabolism; D066298:In Vitro Techniques; D050356:Lipid Metabolism; D008214:Lymphocytes / Q000378:metabolism*; D008297:Male; D008358:Mannose / Q000378:metabolism*; D008970:Molecular Weight; D051381:Rats; D011919:Rats, Inbred Strains; D013154:Spleen / Q000378:metabolism
D004187:Disaccharides; D004224:Diterpenes; D004286:Dolichols; D005936:Glucans; D006023:Glycoproteins; C032438:chitobiose; D008358:Mannose