title: Transmembrane movement of a water-soluble analogue of mannosylphosphoryldolichol is mediated by an endoplasmic reticulum protein.
abstract: Based on topological studies mannosylphosphoryldolichol (Man-P-Dol) is synthesized on the cytoplasmic face of the RER, but functions as a mannosyl donor in Glc3Man9GlcNAc2-P-P-dolichol biosynthesis after the mannosyl-phosphoryl headgroup diffuses transversely to the luminal compartment. The transport of mannosylphosphorylcitronellol (Man-P-Cit), a water-soluble analogue of Man-P-Dol, by microsomal vesicles from mouse liver, has been investigated as a potential experimental approach to determine if a membrane protein(s) mediates the transbilayer movement of Man-P-Dol. For these studies beta-[3H]Man-P-Cit was synthesized enzymatically with a partially purified preparation of Man-P-undecaprenol synthase from Micrococcus luteus. The uptake of the radiolabeled water-soluble analogue was found to be (a) time dependent; (b) stereoselective; (c) dependent on an intact permeability barrier; (d) saturable; (e) protease-sensitive; and (f) highest in ER-enriched vesicles relative to Golgi complex-enriched vesicles and intact mitochondria. Consistent with the involvement of a membrane protein, the analogue did not enter synthetic phosphatidylcholine-liposomes. [3H]Man-P-Cit also was not transported by human erythrocytes. These results indicate that the transport of Man-P-Cit by sealed microsomal vesicles from mouse liver is mediated by a membrane protein transport system. It is possible that the same membrane protein(s) participates in the transbilayer movement of Man-P-Dol in the ER.
authors.affiliation: Department of Biochemistry, University of Kentucky College of Medicine, Lexington 40536, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Rush
authors.forename: C J
authors.initials: CJ
authors.lastname: Waechter
mesh_terms: D000080462:Acyclic Monoterpenes; D000818:Animals; D001692:Biological Transport; D002451:Cell Compartmentation; D002458:Cell Fractionation; D004287:Dolichol Monophosphate Mannose / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism; D006027:Glycosides / Q000737:chemistry; D006801:Humans; D008081:Liposomes / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D008566:Membranes / Q000378:metabolism; D008862:Microsomes, Liver / Q000378:metabolism*; D039821:Monoterpenes; D010713:Phosphatidylcholines / Q000378:metabolism; D051381:Rats; D013237:Stereoisomerism; D013729:Terpenes / Q000737:chemistry; D013997:Time Factors
chemical_list: D000080462:Acyclic Monoterpenes; D006027:Glycosides; D008081:Liposomes; D008565:Membrane Proteins; D039821:Monoterpenes; D010713:Phosphatidylcholines; D013729:Terpenes; D004287:Dolichol Monophosphate Mannose; C007078:citronellol