title: Membrane insertion of the chloroplast outer envelope protein, Toc34: constrains for insertion and topology.
abstract: The insertion of the outer envelope protein Toc34 from chloroplasts was studied. Toc34 was chosen as a model protein because it contains one predicted transmembrane helix at the C-terminus and a large hydrophilic N-terminal located GTPase domain, which is exposed to the cytosol. Unlike proteins located in internal chloroplast compartments, Toc34 neither contains a cleavable presequence nor uses the general import pathway. The protein can insert into the outer envelope of chloroplasts but not into the outer membrane of mitochondria. Using protein-free liposomes we showed that Toc34 is able to insert directly into the lipid bilayer. This insertion is stimulated by GTP and the presence of nonbilayer lipids, but is independent of the presence or absence of charged lipids. The topology of the protein inserted into protein-free liposomes was not exclusively directed by the positive-inside rule but by the size of the hydrophilic domain.
authors.affiliation: Department of Botany, Ludwig-Maximilian University Munich, 80368 Munich, Germany.
authors.forename: Soumya
authors.initials: S
authors.lastname: Qbadou
authors.forename: Roselynn
authors.initials: R
authors.lastname: Tien
authors.forename: Jürgen
authors.initials: J
authors.lastname: Soll
authors.forename: Enrico
authors.initials: E
authors.lastname: Schleiff
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000595:Amino Acid Sequence; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism*; D008051:Lipid Bilayers / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary
chemical_list: D008051:Lipid Bilayers; D008081:Liposomes; D008565:Membrane Proteins; D010940:Plant Proteins; C112475:Toc34 protein, plant; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate