title: Characterization of the translocon of the outer envelope of chloroplasts.
abstract: The protein translocon of the outer envelope of chloroplasts (Toc) consists of the core subunits Toc159, Toc75, and Toc34. To investigate the molecular structure, the core complex was purified. This core complex has an apparent molecular mass of approximately 500 kD and a molecular stoichiometry of 1:4:4-5 between Toc159, Toc75, and Toc34. The isolated translocon recognizes both transit sequences and precursor proteins in a GTP-dependent manner, suggesting its functional integrity. The complex is embedded by the lipids phosphatidylcholine and digalactosyldiacylglyceride. Two-dimensional structural analysis by EM revealed roughly circular particles consistent with the formation of a stable core complex. The particles show a diameter of approximately 130 A with a solid ring and a less dense interior structure. A three-dimensional map obtained by random conical tilt reconstruction of electron micrographs suggests that a "finger"-like central region separates four curved translocation channels within one complex.
authors.affiliation: Botanisches Institut, Ludwig Maximilian Universität München, 80638 München, Germany. schleiff@botanik.biologie.uni-muenchen.de
authors.forename: Enrico
authors.initials: E
authors.lastname: Schleiff
authors.forename: Jürgen
authors.initials: J
authors.lastname: Soll
authors.forename: Michael
authors.initials: M
authors.lastname: Küchler
authors.forename: Werner
authors.initials: W
authors.lastname: Kühlbrandt
authors.forename: Roswitha
authors.initials: R
authors.lastname: Harrer
mesh_terms: D029681:Arabidopsis Proteins; D002736:Chloroplasts / Q000737:chemistry / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D038983:Galactolipids / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D008055:Lipids / Q000737:chemistry; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008854:Microscopy, Electron; D008958:Models, Molecular; D008970:Molecular Weight; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011498:Protein Precursors / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D021381:Protein Transport / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; D038983:Galactolipids; D008055:Lipids; D046911:Macromolecular Substances; D008565:Membrane Proteins; C103933:OEP75 protein precursor, plant; D010940:Plant Proteins; D011498:Protein Precursors; C403444:TOC159 protein, Arabidopsis; C491798:TOC34 protein, Arabidopsis; C491244:TOC75 protein, Arabidopsis; C112475:Toc34 protein, plant; C009909:monogalactosyldiacylglycerol; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases