title: Biosynthesis of glycophospholipid bound and secreted murine class I Qa-2 polypeptides.
abstract: Murine T cells synthesize and express a cell-surface glycophospholipid anchored 40 kDa and a secreted water-soluble 39 kDa Qa-2 polypeptide. We have examined the biosynthetic pathways which lead to the production of the membrane-bound and water-soluble isoforms of the Qa-2 molecule. Using the detergent TX-114, both detergent (membrane)-bound and soluble Qa-2 polypeptides can be identified in cell lysates and can be distinguished by charge and molecular weight. Two membrane-bound forms, a 40-kDa Endo H resistant cell-surface form and a 38 kDa-Endo H sensitive form can be identified, both of which can be biosynthetically labeled with 3H-ethanolamine and can be converted to water soluble forms by digestion with a phosphatidylinositol specific phospholipase C. In addition, several water soluble polypeptides at 39, 37, 35 kDa, and a minor species at 33 kDa were identified, none of which radiolabel with 3H-ethanolamine. While the 39-kDa polypeptide was Endo H resistant, the other isoforms were sensitive to Endo H digestion. Pulse chase experiments and molecular weights of the deglycosylated core polypeptides suggest a precursor to product relationship between the intracellular water-soluble species and the mature 39-kDa secreted Qa-2 molecule. This relationship is supported by the observation that murine L cells transfected with the Qa-2 encoding class I gene Q7 fail to express membrane-bound Qa-2 molecules yet synthesize both intracellular water-soluble and secreted Qa-2 molecules. These findings argue for a pathway in which secreted soluble Qa-2 molecules are derived from intracellular precursors.
authors.affiliation: BRB/NIAID/NIH, Bethesda, MD 20892.
authors.forename: G P
authors.initials: GP
authors.lastname: Einhorn
authors.forename: L
authors.initials: L
authors.lastname: Qin
authors.forename: M J
authors.initials: MJ
authors.lastname: Soloski
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000276:immunology; D002478:Cells, Cultured; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D005786:Gene Expression Regulation / Q000187:drug effects; D006017:Glycolipids / Q000502:physiology*; D015395:Histocompatibility Antigens Class I / Q000096:biosynthesis*; D066298:In Vitro Techniques; D007519:Isoantigens; D008297:Male; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D010743:Phospholipids / Q000502:physiology*; D011233:Precipitin Tests; D013601:T-Lymphocytes / Q000276:immunology
chemical_list: D006017:Glycolipids; D015395:Histocompatibility Antigens Class I; D007519:Isoantigens; D010743:Phospholipids; C032907:Q surface antigens; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase