title: Effect of glycosylphosphatidylinositol anchor-dependent and -independent prion protein association with model raft membranes on conversion to the protease-resistant isoform.
abstract: Prion protein (PrP) is usually bound to membranes by a glycosylphosphatidylinositol (GPI) anchor that associates with detergent-resistant membranes, or rafts. To examine the effect of membrane association on the interaction between the normal protease-sensitive PrP isoform (PrP-sen) and the protease-resistant isoform (PrP-res), a model system was employed using PrP-sen reconstituted into sphingolipid-cholesterol-rich raft-like liposomes (SCRLs). Both full-length (GPI(+)) and GPI anchor-deficient (GPI(-)) PrP-sen produced in fibroblasts stably associated with SCRLs. The latter, alternative mode of membrane association was not detectably altered by glycosylation and was markedly reduced by deletion of residues 34-94. The SCRL-associated PrP molecules were not removed by treatments with either high salt or carbonate buffer. However, only GPI(+) PrP-sen resisted extraction with cold Triton X-100. PrP-sen association with SCRLs was pH-independent. PrP-sen was also one of a small subset of phosphatidylinositol-specific phospholipase C (PI-PLC)-released proteins from fibroblast cells found to bind SCRLs. A cell-free conversion assay was used to measure the interaction of SCRL-bound PrP-sen with exogenous PrP-res as contained in microsomes. SCRL-bound GPI(+) PrP-sen was not converted to PrP-res until PI-PLC was added to the reaction or the combined membrane fractions were treated with the membrane-fusing agent polyethylene glycol (PEG). In contrast, SCRL-bound GPI(-) PrP-sen was converted to PrP-res without PI-PLC or PEG treatment. Thus, of the two forms of raft membrane association by PrP-sen, only the GPI anchor-directed form resists conversion induced by exogenous PrP-res.
authors.affiliation: Laboratory of Persistent Viral Diseases, Rocky Mountain Laboratories, NIAID, National Institutes of Health, Hamilton, Montana 59840, USA.
authors.forename: Gerald S
authors.initials: GS
authors.lastname: Baron
authors.forename: Byron
authors.initials: B
authors.lastname: Caughey
mesh_terms: D000818:Animals; D006224:Cricetinae; D010450:Endopeptidases / Q000378:metabolism*; D005347:Fibroblasts; D017261:Glycosylphosphatidylinositols / Q000378:metabolism* / Q000494:pharmacology; D057927:Hydrophobic and Hydrophilic Interactions; D021962:Membrane Microdomains / Q000378:metabolism*; D051379:Mice; D017830:Octoxynol / Q000494:pharmacology; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D018621:PrPC Proteins / Q000378:metabolism*; D011485:Protein Binding; D020033:Protein Isoforms / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D017261:Glycosylphosphatidylinositols; D018621:PrPC Proteins; D020033:Protein Isoforms; D017830:Octoxynol; D010738:Type C Phospholipases; D054801:Phosphoinositide Phospholipase C; D010450:Endopeptidases; D043265:Phosphatidylinositol Diacylglycerol-Lyase