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Hao B, Zhou W, Theg SM. The polar amino acid in the TatA transmembrane helix is not strictly necessary for protein function. J Biol Chem 2023; 299:102998. [PMID: 36764519 PMCID: PMC10124905 DOI: 10.1016/j.jbc.2023.102998] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Revised: 01/29/2023] [Accepted: 02/01/2023] [Indexed: 02/11/2023] Open
Abstract
The twin-arginine translocation (Tat) pathway utilizes the proton-motive force (pmf) to transport folded proteins across cytoplasmic membranes in bacteria and archaea, as well as across the thylakoid membrane in plants and the inner membrane in mitochondria. In most species, the minimal components required for Tat activity consist of three subunits, TatA, TatB, and TatC. Previous studies have shown that a polar amino acid is present at the N-terminus of the TatA transmembrane helix (TMH) across many different species. In order to systematically assess the functional importance of this polar amino acid in the TatA TMH in Escherichia coli, we examined a complete set of 19-amino-acid substitutions. Unexpectedly, although being preferred overall, our experiments suggest that the polar amino acid is not necessary for a functional TatA. Hydrophilicity and helix-stabilizing properties of this polar amino acid were found to be highly correlated with the Tat activity. Specifically, change in charge status of the amino acid side chain due to pH resulted in a shift in hydrophilicity, which was demonstrated to impact the Tat transport activity. Furthermore, we identified a four-residue motif at the N-terminus of the TatA TMH by sequence alignment. Using a biochemical approach, we found that the N-terminal motif was functionally significant, with evidence indicating a potential role in the preference for utilizing different pmf components. Taken together, these findings yield new insights into the functionality of TatA and its potential role in the Tat transport mechanism.
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Affiliation(s)
- Binhan Hao
- Plant Biology Department, University of California, Davis, California, USA
| | - Wenjie Zhou
- Plant Biology Department, University of California, Davis, California, USA
| | - Steven M Theg
- Plant Biology Department, University of California, Davis, California, USA.
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Hao B, Zhou W, Theg SM. Hydrophobic mismatch is a key factor in protein transport across lipid bilayer membranes via the Tat pathway. J Biol Chem 2022; 298:101991. [PMID: 35490783 PMCID: PMC9207671 DOI: 10.1016/j.jbc.2022.101991] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Revised: 04/13/2022] [Accepted: 04/19/2022] [Indexed: 11/28/2022] Open
Abstract
The twin-arginine translocation (Tat) pathway transports folded proteins across membranes in bacteria, thylakoids, plant mitochondria, and archaea. In most species, the active Tat machinery consists of three independent subunits: TatA, TatB, and TatC. TatA and TatB possess short transmembrane alpha helices (TMHs), both of which are only 15 residues long in Escherichia coli. Such short TMHs cause a hydrophobic mismatch between Tat subunits and the membrane bilayer, although the functional significance of this mismatch is unclear. Here, we sought to address the functional importance of the hydrophobic mismatch in the Tat transport mechanism in E. coli. We conducted three different assays to evaluate the effect of TMH length mutants on Tat activity and observed that the TMHs of TatA and TatB appear to be evolutionarily tuned to 15 amino acids, with activity dropping off following any modification of this length. Surprisingly, TatA and TatB with as few as 11 residues in their TMHs can still insert into the membrane bilayer, albeit with a decline in membrane integrity. These findings support a model of Tat transport utilizing localized toroidal pores that form when the membrane bilayer is thinned to a critical threshold. In this context, we conclude that the 15-residue length of the TatA and TatB TMHs can be seen as a compromise between the need for some hydrophobic mismatch to allow the membrane to reversibly reach the threshold thinness required for toroidal pore formation and the permanently destabilizing effect of placing even shorter helices into these energy-transducing membranes.
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Affiliation(s)
- Binhan Hao
- Plant Biology Department, University of California, Davis, CA 95616
| | - Wenjie Zhou
- Plant Biology Department, University of California, Davis, CA 95616
| | - Steven M Theg
- Plant Biology Department, University of California, Davis, CA 95616.
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Kleiner FH, Vesteg M, Steiner JM. An ancient glaucophyte c6-like cytochrome related to higher plant cytochrome c6A is imported into muroplasts. J Cell Sci 2021; 134:261815. [DOI: 10.1242/jcs.255901] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Accepted: 03/29/2021] [Indexed: 12/13/2022] Open
Abstract
Abstract
Cytochrome c6 is a redox carrier in the thylakoid lumen of cyanobacteria and some eukaryotic algae. Although the isofunctional plastocyanin is present in land plants and the green alga Chlamydomonas reinhardtii, these organisms also possess a cytochrome c6-like protein designated as cytochrome c6A. Two other cytochrome c6-like groups, c6B and c6C, have been identified in cyanobacteria. In this study, we have identified a novel c6-like cytochrome called PetJ2, which is encoded in the nuclear genome of Cyanophora paradoxa, a member of the glaucophytes – the basal branch of the Archaeplastida. We propose that glaucophyte PetJ2 protein is related to cyanobacterial c6B and c6C cytochromes, and that cryptic green algal and land plant cytochromes c6A evolved from an ancestral archaeplastidial PetJ2 protein. In vitro import experiments with isolated muroplasts revealed that PetJ2 is imported into plastids. Although it harbors a twin-arginine motif in its thylakoid-targeting peptide, which is generally indicative of thylakoid import via the Tat import pathway, our import experiments with isolated muroplasts and the heterologous pea thylakoid import system revealed that PetJ2 uses the Sec pathway instead of the Tat import pathway.
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Affiliation(s)
- Friedrich Hans Kleiner
- Institute of Biology – Plant Physiology, Martin Luther University Halle-Wittenberg, Halle/Saale 06099, Germany
- Marine Biological Association, The Laboratory, Citadel Hill, Plymouth PL1 2PB, UK
- School of Ocean and Earth Science, University of Southampton, Southampton SO14 3ZH, UK
| | - Matej Vesteg
- Department of Biology and Ecology, Faculty of Natural Sciences, Matej Bel University, 974 01, Banská Bystrica, Slovakia
| | - Jürgen Michael Steiner
- Institute of Biology – Plant Physiology, Martin Luther University Halle-Wittenberg, Halle/Saale 06099, Germany
- Department of Biology and Ecology, Faculty of Natural Sciences, Matej Bel University, 974 01, Banská Bystrica, Slovakia
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Zinecker S, Jakob M, Klösgen RB. Functional reconstitution of TatB into the thylakoidal Tat translocase. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2019; 1867:118606. [PMID: 31733260 DOI: 10.1016/j.bbamcr.2019.118606] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Revised: 10/22/2019] [Accepted: 10/29/2019] [Indexed: 12/11/2022]
Abstract
We have established an experimental system for the functional analysis of thylakoidal TatB, a component of the membrane-integral TatBC receptor complex of the thylakoidal Twin-arginine protein transport (Tat) machinery. For this purpose, the intrinsic TatB activity of isolated pea thylakoids was inhibited by affinity-purified antibodies and substituted by supplementing the assays with TatB protein either obtained by in vitro translation or purified after heterologous expression in E. coli. Tat transport activity of such reconstituted thylakoids, which was analysed with the authentic Tat substrate pOEC16, reached routinely 20-25% of the activity of mock-treated thylakoid vesicles analysed in parallel. In contrast, supplementation of the assays with the purified antigen comprising all but the N-terminal transmembrane helix of thylakoidal TatB did not result in Tat transport reconstitution which confirms that transport relies strictly on the activity of the TatB protein added and is not due to restoration of the intrinsic TatB activity by antibody release. Unexpectedly, even a mutated TatB protein (TatB,E10C) assumed to be incapable of assembling into the TatBC receptor complex showed low but considerable transport reconstitution underlining the sensitivity of the approach and its suitability for further functional analyses of protein variants. Finally, quantification of TatB demand suggests that TatA and TatB are required in approximately equimolar amounts to achieve Tat-dependent thylakoid transport.
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Affiliation(s)
- Sarah Zinecker
- Institute of Biology - Plant Physiology, Martin Luther University Halle-Wittenberg, Weinbergweg 10, 06120 Halle/Saale, Germany
| | - Mario Jakob
- Institute of Biology - Plant Physiology, Martin Luther University Halle-Wittenberg, Weinbergweg 10, 06120 Halle/Saale, Germany
| | - Ralf Bernd Klösgen
- Institute of Biology - Plant Physiology, Martin Luther University Halle-Wittenberg, Weinbergweg 10, 06120 Halle/Saale, Germany.
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Fröbel J, Blümmel AS, Drepper F, Warscheid B, Müller M. Surface-exposed domains of TatB involved in the structural and functional assembly of the Tat translocase in Escherichia coli. J Biol Chem 2019; 294:13902-13914. [PMID: 31341014 DOI: 10.1074/jbc.ra119.009298] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Revised: 07/10/2019] [Indexed: 11/06/2022] Open
Abstract
Twin-arginine-dependent translocases transport folded proteins across bacterial, archaeal, and chloroplast membranes. Upon substrate binding, they assemble from hexahelical TatC and single-spanning TatA and TatB membrane proteins. Although structural and functional details of individual Tat subunits have been reported previously, the sequence and dynamics of Tat translocase assembly remain to be determined. Employing the zero-space cross-linker N,N'-dicyclohexylcarbodiimide (DCCD) in combination with LC-MS/MS, we identified as yet unknown intra- and intermolecular contact sites of TatB and TatC. In addition to their established intramembrane binding sites, both proteins were thus found to contact each other through the soluble N terminus of TatC and the interhelical linker region around the conserved glutamyl residue Glu49 of TatB from Escherichia coli Functional analyses suggested that by interacting with the TatC N terminus, TatB improves the formation of a proficient substrate recognition site of TatC. The Glu49 region of TatB was found also to contact distinct downstream sites of a neighboring TatB molecule and to thereby mediate oligomerization of TatB within the TatBC receptor complex. Finally, we show that global DCCD-mediated cross-linking of TatB and TatC in membrane vesicles or, alternatively, creating covalently linked TatC oligomers prevents TatA from occupying a position close to the TatBC-bound substrate. Collectively, our results are consistent with a circular arrangement of the TatB and TatC units within the TatBC receptor complex and with TatA entering the interior TatBC-binding cavity through lateral gates between TatBC protomers.
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Affiliation(s)
- Julia Fröbel
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany
| | - Anne-Sophie Blümmel
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany
| | - Friedel Drepper
- Institute of Biology II, Biochemistry-Functional Proteomics, Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany.,BIOSS Centre for Biological Signalling Studies, University of Freiburg, 79104 Freiburg, Germany
| | - Bettina Warscheid
- Institute of Biology II, Biochemistry-Functional Proteomics, Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany.,BIOSS Centre for Biological Signalling Studies, University of Freiburg, 79104 Freiburg, Germany.,CIBSS Centre for Integrative Biological Signalling Studies, University of Freiburg, 79104 Freiburg, Germany
| | - Matthias Müller
- Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany
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New CP, Ma Q, Dabney-Smith C. Routing of thylakoid lumen proteins by the chloroplast twin arginine transport pathway. PHOTOSYNTHESIS RESEARCH 2018; 138:289-301. [PMID: 30101370 DOI: 10.1007/s11120-018-0567-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Accepted: 07/26/2018] [Indexed: 06/08/2023]
Abstract
Thylakoids are complex sub-organellar membrane systems whose role in photosynthesis makes them critical to life. Thylakoids require the coordinated expression of both nuclear- and plastid-encoded proteins to allow rapid response to changing environmental conditions. Transport of cytoplasmically synthesized proteins to thylakoids or the thylakoid lumen is complex; the process involves transport across up to three membrane systems with routing through three aqueous compartments. Protein transport in thylakoids is accomplished by conserved ancestral prokaryotic plasma membrane translocases containing novel adaptations for the sub-organellar location. This review focuses on the evolutionarily conserved chloroplast twin arginine transport (cpTat) pathway. An overview is provided of known aspects of the cpTat components, energy requirements, and mechanisms with a focus on recent discoveries. Some of the most exciting new studies have been in determining the structural architecture of the membrane complex involved in forming the point of passage for the precursor and binding features of the translocase components. The cpTat system is of particular interest because it transports folded protein domains using only the proton motive force for energy. The implications for mechanism of translocation by recent studies focusing on interactions between membrane Tat components and with the translocating precursor will be discussed.
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Affiliation(s)
- Christopher Paul New
- Cellular, Molecular, and Structural Biology Graduate Program, Miami University, Oxford, OH, 45056, USA
| | - Qianqian Ma
- Cellular, Molecular, and Structural Biology Graduate Program, Miami University, Oxford, OH, 45056, USA
| | - Carole Dabney-Smith
- Cellular, Molecular, and Structural Biology Graduate Program, Miami University, Oxford, OH, 45056, USA.
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH, 45056, USA.
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Hou B, Heidrich ES, Mehner-Breitfeld D, Brüser T. The TatA component of the twin-arginine translocation system locally weakens the cytoplasmic membrane of Escherichia coli upon protein substrate binding. J Biol Chem 2018. [PMID: 29535185 DOI: 10.1074/jbc.ra118.002205] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The twin-arginine translocation (Tat) system that comprises the TatA, TatB, and TatC components transports folded proteins across energized membranes of prokaryotes and plant plastids. It is not known, however, how the transport of this protein cargo is achieved. Favored models suggest that the TatA component supports transport by weakening the membrane upon full translocon assembly. Using Escherichia coli as a model organism, we now demonstrate in vivo that the N terminus of TatA can indeed destabilize the membrane, resulting in a lowered membrane energization in growing cells. We found that in full-length TatA, this effect is counterbalanced by its amphipathic helix. Consistent with these observations, the TatA N terminus induced proton leakage in vitro, indicating membrane destabilization. Fluorescence quenching data revealed that substrate binding causes the TatA hinge region and the N-terminal part of the TatA amphipathic helix to move toward the membrane surface. In the presence of TatBC, substrate binding also reduced the exposure of a specific region in the amphipathic helix, indicating a participation of TatBC. Of note, the substrate-induced reorientation of the TatA amphipathic helix correlated with detectable membrane weakening. We therefore propose a two-state model in which membrane-destabilizing effects of the short TatA membrane anchor are compensated by the membrane-immersed N-terminal part of the amphipathic helix in a resting state. We conclude that substrate binding to TatABC complexes switches the position of the amphipathic helix, which locally weakens the membrane on demand to allow substrate translocation across the membrane.
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Affiliation(s)
- Bo Hou
- From the Institute of Microbiology, Leibniz Universität Hannover, Herrenhäuser Strasse 2, 30419 Hannover, Germany
| | - Eyleen S Heidrich
- From the Institute of Microbiology, Leibniz Universität Hannover, Herrenhäuser Strasse 2, 30419 Hannover, Germany
| | - Denise Mehner-Breitfeld
- From the Institute of Microbiology, Leibniz Universität Hannover, Herrenhäuser Strasse 2, 30419 Hannover, Germany
| | - Thomas Brüser
- From the Institute of Microbiology, Leibniz Universität Hannover, Herrenhäuser Strasse 2, 30419 Hannover, Germany
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