title: Characterization of abnormal free glycophosphatidylinositols accumulating in mutant lymphoma cells of classes B, E, F, and H.
abstract: Several mutant lymphoma lines are unable to add glycophosphatidylinositol membrane anchors to proteins. Some of them accumulate abnormal glycolipids which can be labeled by tritiated myo-inositol, mannose, or ethanolamine and which are not present in the corresponding parental cell lines. The [3H]myo-inositol-labeled abnormal lipids were isolated and characterized using hydrofluoric acid dephosphorylation, nitrous acid deamination, acetolysis, and exoglycosidase treatments alone or in combination. This partial characterization suggests that the class F mutant EL-4-f contains 3 abnormal glycolipids containing 3, 2, or 1 mannose residues, the headgroups of which are Man alpha 1,2Man alpha 1,6(X-->)Man alpha-GlcN-acylinositol, Man alpha 1,6(X-->)Man alpha-GlcN-inositol, and (X-->)Man alpha-GlcN-acylinositol where X represents a charged, hydrofluoric acid-sensitive substituent. A fourth, minor abnormal lipid with a Man alpha 1,6(X-->)Man alpha-GlcN-inositol headgroup but a different lipid moiety is also found. The substituent X is likely to consist of phosphoethanolamine since hydrofluoric acid releases [3H]ethanolamine from the [3H]ethanolamine-labeled version of these lipids. Pulse-chase experiments indicate that the abnormal glycophosphatidylinositols of class F mutants are very long-lived. The class B mutant S1A-b has previously been shown to contain an abnormal Man alpha 1,6(phosphoethanolamine-->)Man alpha-GlcN-acylinositol-P-lipid intermediate. Here we show that S1A-b also accumulates a more polar but less abundant lipid which has the identical headgroup structure but lacks the acyl group on the inositol residue. The class E mutant BW5147-e accumulates a hydrophobic glycolipid with the headgroup structure GlcN-acylinositol. All the abnormal glycolipids except those of EL-4-f are heterogeneous with regard to their lipid moiety since base-resistant as well as base-sensitive lipids are present. This suggests that the base-resistant alkylglycerols typical of mammalian anchors can get integrated into anchors at early stages of glycophosphatidylinositol formation.
authors: Institute of Biochemistry, University of Lausanne, Switzerland.
authors: A
authors: A
authors: Puoti
authors: A
authors: A
authors: Conzelmann
mesh_terms: D000215:Acylation; D000818:Animals; D002240:Carbohydrate Sequence; D002854:Chromatography, Paper; D006017:Glycolipids / Q000378:metabolism; D017261:Glycosylphosphatidylinositols / Q000737:chemistry / Q000378:metabolism*; D008223:Lymphoma / Q000145:classification / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D014407:Tumor Cells, Cultured
chemical_list: D006017:Glycolipids; D017261:Glycosylphosphatidylinositols