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Analysis of the Brucella suis Twin Arginine Translocation System and Its Substrates Shows That It Is Essential for Viability. Infect Immun 2023; 91:e0045922. [PMID: 36448838 PMCID: PMC9872638 DOI: 10.1128/iai.00459-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Bacteria use the twin arginine translocator (Tat) system to export folded proteins from the cytosol to the bacterial envelope or to the extracellular environment. As with most Gram-negative bacteria, the Tat system of the zoonotic pathogen Brucella spp. is encoded by a three-gene operon, tatABC. Our attempts, using several different strategies, to create a Brucella suis strain 1330 tat mutant were all unsuccessful. This suggested that, for B. suis, Tat is essential, in contrast to a recent report for Brucella melitensis. This was supported by our findings that two molecules that inhibit the Pseudomonas aeruginosa Tat system also inhibit B. suis, B. melitensis, and Brucella abortus growth in vitro. In a bioinformatic screen of the B. suis 1330 proteome, we identified 28 proteins with putative Tat signal sequences. We used a heterologous reporter assay based on export of the Tat-dependent amidase AmiA by using the Tat signal sequences from the Brucella proteins to confirm that 20 of the 28 candidates can engage the Tat pathway.
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Taw MN, Boock JT, Sotomayor B, Kim D, Rocco MA, Waraho-Zhmayev D, DeLisa MP. Twin-arginine translocase component TatB performs folding quality control via a chaperone-like activity. Sci Rep 2022; 12:14862. [PMID: 36050356 PMCID: PMC9436932 DOI: 10.1038/s41598-022-18958-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2022] [Accepted: 08/23/2022] [Indexed: 12/03/2022] Open
Abstract
The twin-arginine translocation (Tat) pathway involves an inbuilt quality control (QC) system that synchronizes the proofreading of substrate protein folding with lipid bilayer transport. However, the molecular details of this QC mechanism remain poorly understood. Here, we hypothesized that the conformational state of Tat substrates is directly sensed by the TatB component of the bacterial Tat translocase. In support of this hypothesis, several TatB variants were observed to form functional translocases in vivo that had compromised QC activity as evidenced by the uncharacteristic export of several misfolded protein substrates. These variants each possessed cytoplasmic membrane-extrinsic domains that were either truncated or mutated in the vicinity of a conserved, highly flexible α-helical domain. In vitro folding experiments revealed that the TatB membrane-extrinsic domain behaved like a general molecular chaperone, transiently binding to highly structured, partially unfolded intermediates of a model protein, citrate synthase, in a manner that prevented its irreversible aggregation and stabilized the active species. Collectively, these results suggest that the Tat translocase may use chaperone-like client recognition to monitor the conformational status of its substrates.
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Affiliation(s)
- May N Taw
- Department of Microbiology, Cornell University, Ithaca, NY, 14853, USA
| | - Jason T Boock
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, 120 Olin Hall, Ithaca, NY, 14853, USA
| | - Belen Sotomayor
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, 120 Olin Hall, Ithaca, NY, 14853, USA
| | - Daniel Kim
- Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, 120 Olin Hall, Ithaca, NY, 14853, USA
| | - Mark A Rocco
- Nancy E. and Peter C. Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY, 14853, USA
| | - Dujduan Waraho-Zhmayev
- Biological Engineering Program, Faculty of Engineering, King Mongkut's University of Technology Thonburi, Bangkok, Thailand
| | - Matthew P DeLisa
- Department of Microbiology, Cornell University, Ithaca, NY, 14853, USA. .,Robert Frederick Smith School of Chemical and Biomolecular Engineering, Cornell University, 120 Olin Hall, Ithaca, NY, 14853, USA. .,Nancy E. and Peter C. Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY, 14853, USA.
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Palmer T, Stansfeld PJ. Targeting of proteins to the twin-arginine translocation pathway. Mol Microbiol 2020; 113:861-871. [PMID: 31971282 PMCID: PMC7317946 DOI: 10.1111/mmi.14461] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 01/12/2020] [Accepted: 01/12/2020] [Indexed: 02/06/2023]
Abstract
The twin-arginine protein transport (Tat pathway) is found in prokaryotes and plant organelles and transports folded proteins across membranes. Targeting of substrates to the Tat system is mediated by the presence of an N-terminal signal sequence containing a highly conserved twin-arginine motif. The Tat machinery comprises membrane proteins from the TatA and TatC families. Assembly of the Tat translocon is dynamic and is triggered by the interaction of a Tat substrate with the Tat receptor complex. This review will summarise recent advances in our understanding of Tat transport, focusing in particular on the roles played by Tat signal peptides in protein targeting and translocation.
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Affiliation(s)
- Tracy Palmer
- Faculty of Medical Sciences, Centre for Bacterial Cell Biology, Biosciences Institute, Molecular and Cellular Microbiology Theme, Newcastle University, Newcastle upon Tyne, England
| | - Phillip J Stansfeld
- School of Life Sciences and Department of Chemistry, University of Warwick, Coventry, UK
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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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Abstract
The inner membrane of Gram-negative bacteria is a ~6 nm thick phospholipid bilayer. It forms a semi-permeable barrier between the cytoplasm and periplasm allowing only regulated export and import of ions, sugar polymers, DNA and proteins. Inner membrane proteins, embedded via hydrophobic transmembrane α-helices, play an essential role in this regulated trafficking: they mediate insertion into the membrane (insertases) or complete crossing of the membrane (translocases) or both. The Gram-negative inner membrane is equipped with a variety of different insertases and translocases. Many of them are specialized, taking care of the export of only a few protein substrates, while others have more general roles. Here, we focus on the three general export/insertion pathways, the secretory (Sec) pathway, YidC and the twin-arginine translocation (TAT) pathway, focusing closely on the Escherichia coli (E. coli) paradigm. We only briefly mention dedicated export pathways found in different Gram-negative bacteria. The Sec system deals with the majority of exported proteins and functions both as a translocase for secretory proteins and an insertase for membrane proteins. The insertase YidC assists the Sec system or operates independently on membrane protein clients. Sec and YidC, in common with most export pathways, require their protein clients to be in soluble non-folded states to fit through the translocation channels and grooves. The TAT pathway is an exception, as it translocates folded proteins, some loaded with prosthetic groups.
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Affiliation(s)
- Jozefien De Geyter
- Laboratory of Molecular Bacteriology, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven - University of Leuven, Herestraat 49, 3000, Leuven, Belgium
| | - Dries Smets
- Laboratory of Molecular Bacteriology, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven - University of Leuven, Herestraat 49, 3000, Leuven, Belgium
| | - Spyridoula Karamanou
- Laboratory of Molecular Bacteriology, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven - University of Leuven, Herestraat 49, 3000, Leuven, Belgium
| | - Anastassios Economou
- Laboratory of Molecular Bacteriology, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven - University of Leuven, Herestraat 49, 3000, Leuven, Belgium.
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