title: Polypeptide Transport-Associated Domains of the Toc75 Channel Protein Are Located in the Intermembrane Space of Chloroplasts.
abstract: Toc75 is the channel for protein translocation across the chloroplast outer envelope membrane. Toc75 belongs to the Omp85 protein family and consists of three N-terminal polypeptide transport-associated (POTRA) domains that are essential for the functions of Toc75, followed by a membrane-spanning β-barrel domain. In bacteria, POTRA domains of Omp85 family members are located in the periplasm, where they interact with other partner proteins to accomplish protein secretion and outer membrane protein assembly. However, the orientation and therefore the molecular function of chloroplast Toc75 POTRA domains remain a matter of debate. We investigated the topology of Toc75 using bimolecular fluorescence complementation and immunogold electron microscopy. Bimolecular fluorescence complementation analyses showed that in stably transformed plants, Toc75 N terminus is located on the intermembrane space side, not the cytosolic side, of the outer membrane. Immunogold labeling of endogenous Toc75 POTRA domains in pea (Pisum sativum) and Arabidopsis (Arabidopsis thaliana) confirmed that POTRA domains are located in the intermembrane space of the chloroplast envelope.
authors.affiliation: Institute of Molecular Biology, Academia Sinica, Nankang, Taipei 11529, Taiwan.
authors.forename: Yih-Lin
authors.identifier: 0000-0003-1151-1706
authors.initials: YL
authors.lastname: Chen
authors.affiliation: Institute of Molecular Biology, Academia Sinica, Nankang, Taipei 11529, Taiwan.
authors.forename: Lih-Jen
authors.initials: LJ
authors.lastname: Chen
authors.affiliation: Institute of Molecular Biology, Academia Sinica, Nankang, Taipei 11529, Taiwan mbhmli@gate.sinica.edu.tw.
authors.forename: Hsou-Min
authors.identifier: 0000-0002-0211-7339
authors.initials: HM
authors.lastname: Li
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D002736:Chloroplasts / Q000378:metabolism* / Q000648:ultrastructure; D015151:Immunoblotting; D007425:Intracellular Membranes / Q000378:metabolism* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D018613:Microscopy, Confocal; D016253:Microscopy, Immunoelectron; D018532:Pisum sativum / Q000235:genetics / Q000378:metabolism; D010455:Peptides / Q000378:metabolism*; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport
chemical_list: D029681:Arabidopsis Proteins; D008565:Membrane Proteins; D010455:Peptides; D010940:Plant Proteins; D011498:Protein Precursors; C491244:TOC75 protein, Arabidopsis