title: Oligomers of Tha4 organize at the thylakoid Tat translocase during protein transport.
abstract: The Tat (twin arginine translocation) systems of thylakoids and bacteria transport fully folded protein substrates without breaching the permeability barrier of the membrane. Two components of the thylakoid system, cpTatC and Hcf106, compose a precursor-bound receptor complex. The third component, Tha4, assembles with the precursor-bound receptor complex for the translocation step and is thought to compose at least part of the protein-conducting channel. Here, we used two different cross-linking approaches to explore the organization of Tha4 in the translocase. These cross-linking techniques showed that transition to an active protein transport state resulted in an alignment of the Tha4 amphipathic helix and C-terminal tail domains to form Tha4 oligomers. Oligomerization required functional Tha4, a twin arginine signal peptide, and an active cpTatC-Hcf106 receptor complex. The spectrum of oligomers obtained was independent of the mature folded domain of the precursor. We propose a trapdoor mechanism for translocation whereby aligned oligomers of Tha4 amphipathic helices fold into the membrane to allow formfitting passage of precursor proteins.
authors.affiliation: Horticultural Sciences Department and the Plant Molecular and Cellular Biology Program, University of Florida, 1109 Fifield Hall, Gainesville, FL 32611, USA.
authors.forename: Carole
authors.initials: C
authors.lastname: Dabney-Smith
authors.forename: Hiroki
authors.initials: H
authors.lastname: Mori
authors.forename: Kenneth
authors.initials: K
authors.lastname: Cline
mesh_terms: D000595:Amino Acid Sequence; D001120:Arginine / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000378:metabolism; D004220:Disulfides; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D018532:Pisum sativum / Q000166:cytology / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D011498:Protein Precursors / Q000378:metabolism; D021381:Protein Transport; D020524:Thylakoids / Q000378:metabolism*
chemical_list: D003432:Cross-Linking Reagents; D004220:Disulfides; D008565:Membrane Proteins; D010940:Plant Proteins; D011498:Protein Precursors; C120444:Tha4 protein, plant; D001120:Arginine