title: Lipoprotein-like particles in a prokaryote: quinone droplets of Thermoplasma acidophilum.
abstract: Cytosolic, globular droplets with an average diameter of 50 nm were observed in vitrified Thermoplasma acidophilum cells by means of cryo-electron tomography. These droplets were isolated by column chromatography and immunoprecipitation protein purification methods. Subsequent chemical and biochemical analyses identified lipid and protein components, respectively. Two major lipid components, comigrating menaquinones at the solvent front and the slower migrating Thermoplasma polar lipid U4, were detected by TLC experiments. The major protein component was identified as the 153 amino acid long Ta0547 vitellogenin-N domain protein. This domain has been found so far exclusively in large lipid transport proteins of vertebrates and non-vertebrates. Blast protein database homology searches with Ta0547 did not return any eukaryal hits; homologous sequences were found only in thermo-acidophilic archaeons. However, a profile-sequence domain search performed with the vitellogenin-N domain (PF01347) hmm-profile against the T. acidophilum proteome returned Ta0547 as hit. Electron microscopy appearance of isolated droplets resembled to lipoprotein particles. However, no (tetraether) lipid layer could be detected on the droplets surface, rather hydrophobic compounds of the electron dense lumen were surrounded by a denser discontinuous protein boundary. Based on described features, these particles qualify for a novel lipoprotein particle category, what we nominated Thermoplasma Quinone Droplet.
authors.affiliation: Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, D-82152 Martinsried (Planegg), Germany nagy@biochem.mpg.de.
authors.forename: István
authors.initials: I
authors.lastname: Nagy
authors.affiliation: Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, D-82152 Martinsried (Planegg), Germany.
authors.forename: Roland Wilhelm
authors.initials: RW
authors.lastname: Knispel
authors.affiliation: Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, D-82152 Martinsried (Planegg), Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Kofler
authors.affiliation: Istituto Zooprofilattico dell'Abruzzo e del Molise; Campo Boario, 64100 Teramo, Italy.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Orsini
authors.affiliation: Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, D-82152 Martinsried (Planegg), Germany.
authors.forename: Marius
authors.initials: M
authors.lastname: Boicu
authors.affiliation: Department of Applied and Environmental Microbiology, Research Institute of Agro-Environmental Sciences, National Agricultural Research and Innovation Centre, Budapest, H-1022 Budapest, Hungary.
authors.forename: Sándor
authors.initials: S
authors.lastname: Varga
authors.affiliation: Max Planck Institute of Biochemistry, Core Facility, D-82152 Martinsried (Planegg), Germany.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Weyher-Stingl
authors.affiliation: Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, D-82152 Martinsried (Planegg), Germany.
authors.forename: Na
authors.initials: N
authors.lastname: Sun
authors.affiliation: Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, D-82152 Martinsried (Planegg), Germany.
authors.forename: Ruben
authors.initials: R
authors.lastname: Fernandez-Busnadiego
authors.affiliation: Department of Applied and Environmental Microbiology, Research Institute of Agro-Environmental Sciences, National Agricultural Research and Innovation Centre, Budapest, H-1022 Budapest, Hungary.
authors.forename: József
authors.initials: J
authors.lastname: Kukolya
authors.affiliation: Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, D-82152 Martinsried (Planegg), Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Nickell
authors.affiliation: Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, D-82152 Martinsried (Planegg), Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Baumeister
mesh_terms: D016227:Benzoquinones / Q000737:chemistry* / Q000302:isolation & purification; D020285:Cryoelectron Microscopy; D008055:Lipids / Q000737:chemistry / Q000302:isolation & purification; D008074:Lipoproteins / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism; D020543:Proteome; D013822:Thermoplasma / Q000737:chemistry*; D014819:Vitellogenins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification
chemical_list: D016227:Benzoquinones; D008055:Lipids; D008074:Lipoproteins; D020543:Proteome; D014819:Vitellogenins; C004532:quinone
keywords: Ta0547; quinone droplet; thermo-acidophilic archaeon; vitamin K2-7; vitellogenin-N domain protein