title: A twin arginine signal peptide and the pH gradient trigger reversible assembly of the thylakoid [Delta]pH/Tat translocase.
abstract: The thylakoid DeltapH-dependent/Tat pathway is a novel system with the remarkable ability to transport tightly folded precursor proteins using a transmembrane DeltapH as the sole energy source. Three known components of the transport machinery exist in two distinct subcomplexes. A cpTatC-Hcf106 complex serves as precursor receptor and a Tha4 complex is required after precursor recognition. Here we report that Tha4 assembles with cpTatC-Hcf106 during the translocation step. Interactions among components were examined by chemical cross-linking of intact thylakoids followed by immunoprecipitation and immunoblotting. cpTatC and Hcf106 were consistently associated under all conditions tested. In contrast, Tha4 was only associated with cpTatC and Hcf106 in the presence of a functional precursor and the DeltapH. Interestingly, a synthetic signal peptide could replace intact precursor in triggering assembly. The association of all three components was transient and dissipated upon the completion of protein translocation. Such an assembly-disassembly cycle could explain how the DeltapH/Tat system can assemble translocases to accommodate folded proteins of varied size. It also explains in part how the system can exist in the membrane without compromising its ion and proton permeability barrier.
authors.affiliation: Horticultural Sciences and Plant Molecular and Cellular Biology, University of Florida, Gainesville, FL 32611, USA. Britta.J.Eickholt@kcl.ac.uk
authors.forename: Hiroki
authors.initials: H
authors.lastname: Mori
authors.forename: Kenneth
authors.initials: K
authors.lastname: Cline
mesh_terms: D001120:Arginine / Q000378:metabolism*; D003432:Cross-Linking Reagents; D004151:Dipeptides / Q000378:metabolism*; D029968:Escherichia coli Proteins; D006863:Hydrogen-Ion Concentration; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism*; D008954:Models, Biological; D018532:Pisum sativum / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D010957:Plasmids; D011485:Protein Binding; D021382:Protein Sorting Signals / Q000502:physiology*; D021381:Protein Transport; D020524:Thylakoids / Q000737:chemistry / Q000378:metabolism*; D013997:Time Factors
chemical_list: D003432:Cross-Linking Reagents; D004151:Dipeptides; D029968:Escherichia coli Proteins; C109236:Hcf106 protein, plant; D046911:Macromolecular Substances; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D010940:Plant Proteins; D021382:Protein Sorting Signals; C432107:TatC protein, plant; C120444:Tha4 protein, plant; C408585:twin-arginine translocase complex, E coli; D001120:Arginine