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Gallego-Parrilla JJ, Severi E, Chandra G, Palmer T. Identification of novel tail-anchored membrane proteins integrated by the bacterial twin-arginine translocase. MICROBIOLOGY (READING, ENGLAND) 2024; 170:001431. [PMID: 38363712 PMCID: PMC10924467 DOI: 10.1099/mic.0.001431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2023] [Accepted: 01/22/2024] [Indexed: 02/18/2024]
Abstract
The twin-arginine protein transport (Tat) system exports folded proteins across the cytoplasmic membranes of prokaryotes and the energy transducing-membranes of plant thylakoids and mitochondria. Proteins are targeted to the Tat machinery by N-terminal signal peptides with a conserved twin-arginine motif, and some substrates are exported as heterodimers where the signal peptide is present on one of the partner proteins. A subset of Tat substrates is found in the membrane. Tat-dependent membrane proteins usually have large globular domains and a single transmembrane helix present at the N- or C-terminus. Five Tat substrates that have C-terminal transmembrane helices have previously been characterized in the model bacterium Escherichia coli. Each of these is an iron-sulfur cluster-containing protein involved in electron transfer from hydrogen or formate. Here we have undertaken a bioinformatic search to identify further tail-anchored Tat substrates encoded in bacterial genomes. Our analysis has revealed additional tail-anchored iron-sulfur proteins associated in modules with either a b-type cytochrome or a quinol oxidase. We also identified further candidate tail-anchored Tat substrates, particularly among members of the actinobacterial phylum, that are not predicted to contain cofactors. Using reporter assays, we show experimentally that six of these have both N-terminal Tat signal peptides and C-terminal transmembrane helices. The newly identified proteins include a carboxypeptidase and a predicted protease, and four sortase substrates for which membrane integration is a prerequisite for covalent attachment to the cell wall.
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Affiliation(s)
- José Jesús Gallego-Parrilla
- Microbes in Health and Disease Theme, Newcastle University Biosciences Institute, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Emmanuele Severi
- Microbes in Health and Disease Theme, Newcastle University Biosciences Institute, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Govind Chandra
- John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK
| | - Tracy Palmer
- Microbes in Health and Disease Theme, Newcastle University Biosciences Institute, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
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Severi E, Bunoro Batista M, Lannoy A, Stansfeld PJ, Palmer T. Characterization of a TatA/TatB binding site on the TatC component of the Escherichia coli twin arginine translocase. MICROBIOLOGY (READING, ENGLAND) 2023; 169:001298. [PMID: 36790402 PMCID: PMC10197872 DOI: 10.1099/mic.0.001298] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2022] [Accepted: 01/06/2023] [Indexed: 02/16/2023]
Abstract
The twin arginine transport (Tat) pathway exports folded proteins across the cytoplasmic membranes of prokaryotes and the thylakoid membranes of chloroplasts. In Escherichia coli and other Gram-negative bacteria, the Tat machinery comprises TatA, TatB and TatC components. A Tat receptor complex, formed from all three proteins, binds Tat substrates, which triggers receptor organization and recruitment of further TatA molecules to form the active Tat translocon. The polytopic membrane protein TatC forms the core of the Tat receptor and harbours two binding sites for the sequence-related TatA and TatB proteins. A 'polar' cluster binding site, formed by TatC transmembrane helices (TMH) 5 and 6 is occupied by TatB in the resting receptor and exchanges for TatA during receptor activation. The second binding site, lying further along TMH6, is occupied by TatA in the resting state, but its functional relevance is unclear. Here we have probed the role of this second binding site through a programme of random and targeted mutagenesis. Characterization of three stably produced TatC variants, P221R, M222R and L225P, each of which is inactive for protein transport, demonstrated that the substitutions did not affect assembly of the Tat receptor. Moreover, the substitutions that we analysed did not abolish TatA or TatB binding to either binding site. Using targeted mutagenesis we introduced bulky substitutions into the TatA binding site. Molecular dynamics simulations and crosslinking analysis indicated that TatA binding at this site was substantially reduced by these amino acid changes, but TatC retained function. While it is not clear whether TatA binding at the TMH6 site is essential for Tat activity, the isolation of inactivating substitutions indicates that this region of the protein has a critical function.
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Affiliation(s)
- Emmanuele Severi
- Microbes in Health and Disease Theme, Newcastle University Biosciences Institute, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Mariana Bunoro Batista
- School of Life Sciences and Department of Chemistry, Gibbet Hill Campus, University of Warwick, Coventry, CV4 7AL, UK
| | - Adelie Lannoy
- Microbes in Health and Disease Theme, Newcastle University Biosciences Institute, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
| | - Phillip J. Stansfeld
- School of Life Sciences and Department of Chemistry, Gibbet Hill Campus, University of Warwick, Coventry, CV4 7AL, UK
| | - Tracy Palmer
- Microbes in Health and Disease Theme, Newcastle University Biosciences Institute, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK
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Ghosh D, Boral D, Vankudoth KR, Ramasamy S. Analysis of haloarchaeal twin-arginine translocase pathway reveals the diversity of the machineries. Heliyon 2019; 5:e01587. [PMID: 31193317 PMCID: PMC6525301 DOI: 10.1016/j.heliyon.2019.e01587] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2018] [Revised: 03/23/2019] [Accepted: 04/24/2019] [Indexed: 01/10/2023] Open
Abstract
The twin-arginine translocase (Tat) pathway transports folded proteins across the plasma membrane and plays a critical role in protein transport in haloarchaea. Computational analysis and previous experimental evidence suggested that the Tat pathway transports almost the entire secretome in haloarchaea. The TatC, receptor component of this pathway shows greater variation in membrane topology in haloarchaea than in other organisms. The presence of a unique fourteen-transmembrane TatC homolog (TatCt) in haloarchaea, over and above the expected TatC topological variants, indicates a strong correlation between the additional homologs and the large number of substrates transported via the haloarchaeal Tat pathway. Various combinations of TatC homologs with different topologies—TatCo, TatCt, TatCn, and TatCx have been observed in haloarchaea. In this report, on the basis of these combinations we have segregated all haloarchaeal Tat substrates into two groups. The first group consists of substrates that are transported by TatCt alone, whereas the second group consists of substrates that are transported by the other TatC homologs (TatCo, TatCn, and TatCx). The various haloarchaea TatA components also shows the possible segregation towards the substrates. We have also identified the possible homologs for Tat substrate chaperones, which act as a quality-control mechanism for proper protein folding. Further sequence analysis implies that the two TatC domains of TatCt complement each other's functionally. Substrate analysis also revealed subtle differences between the substrates being transported by various homologs: further experimental analysis is therefore required for better understanding of the complexities of the haloarchaeal Tat pathway.
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Affiliation(s)
- Deepanjan Ghosh
- Division of Biochemical Sciences, CSIR-National Chemical Laboratory, Pune 411008, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad- 201002, India
| | - Debjyoti Boral
- Division of Biochemical Sciences, CSIR-National Chemical Laboratory, Pune 411008, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad- 201002, India
| | - Koteswara Rao Vankudoth
- Division of Biochemical Sciences, CSIR-National Chemical Laboratory, Pune 411008, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad- 201002, India
| | - Sureshkumar Ramasamy
- Division of Biochemical Sciences, CSIR-National Chemical Laboratory, Pune 411008, India
- Corresponding author.
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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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5
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Wojnowska M, Gault J, Yong SC, Robinson CV, Berks BC. Precursor-Receptor Interactions in the Twin Arginine Protein Transport Pathway Probed with a New Receptor Complex Preparation. Biochemistry 2018; 57:1663-1671. [PMID: 29460615 PMCID: PMC5852461 DOI: 10.1021/acs.biochem.8b00026] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The twin arginine translocation (Tat) system moves folded proteins across the cytoplasmic membrane of bacteria and the thylakoid membrane of plant chloroplasts. Signal peptide-bearing substrates of the Tat pathway (precursor proteins) are recognized at the membrane by the TatBC receptor complex. The only established preparation of the TatBC complex uses the detergent digitonin, rendering it unsuitable for biophysical analysis. Here we show that the detergent glyco-diosgenin (GDN) can be used in place of digitonin to isolate homogeneous TatBC complexes that bind precursor proteins with physiological specificity. We use this new preparation to quantitatively characterize TatBC-precursor interactions in a fully defined system. Additionally, we show that the GDN-solubilized TatBC complex co-purifies with substantial quantities of phospholipids.
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Affiliation(s)
- Marta Wojnowska
- Department of Biochemistry , University of Oxford , South Parks Road , Oxford OX1 3QU , United Kingdom
| | - Joseph Gault
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry , University of Oxford , South Parks Road , Oxford OX1 3QZ , United Kingdom
| | - Shee Chien Yong
- Department of Biochemistry , University of Oxford , South Parks Road , Oxford OX1 3QU , United Kingdom
| | - Carol V Robinson
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry , University of Oxford , South Parks Road , Oxford OX1 3QZ , United Kingdom
| | - Ben C Berks
- Department of Biochemistry , University of Oxford , South Parks Road , Oxford OX1 3QU , United Kingdom
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Blümmel AS, Drepper F, Knapp B, Eimer E, Warscheid B, Müller M, Fröbel J. Structural features of the TatC membrane protein that determine docking and insertion of a twin-arginine signal peptide. J Biol Chem 2017; 292:21320-21329. [PMID: 29089385 DOI: 10.1074/jbc.m117.812560] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 10/26/2017] [Indexed: 11/06/2022] Open
Abstract
Twin-arginine translocation (Tat) systems transport folded proteins across cellular membranes with the concerted action of mostly three membrane proteins: TatA, TatB, and TatC. Hetero-oligomers of TatB and TatC form circular substrate-receptor complexes with a central binding cavity for twin-arginine-containing signal peptides. After binding of the substrate, energy from an electro-chemical proton gradient is transduced into the recruitment of TatA oligomers and into the actual translocation event. We previously reported that Tat-dependent protein translocation into membrane vesicles of Escherichia coli is blocked by the compound N,N'-dicyclohexylcarbodiimide (DCCD, DCC). We have now identified a highly conserved glutamate residue in the transmembrane region of E. coli TatC, which when modified by DCCD interferes with the deep insertion of a Tat signal peptide into the TatBC receptor complex. Our findings are consistent with a hydrophobic binding cavity formed by TatB and TatC inside the lipid bilayer. Moreover, we found that DCCD mediates discrete intramolecular cross-links of E. coli TatC involving both its N- and C-tails. These results confirm the close proximity of two distant sequence sections of TatC proposed to concertedly function as the primary docking site for twin-arginine signal peptides.
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Affiliation(s)
- Anne-Sophie Blümmel
- From the Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine.,the Spemann Graduate School of Biology and Medicine (SGBM).,the Faculty of Biology
| | - Friedel Drepper
- the Institute of Biology II, Biochemistry: Functional Proteomics, Faculty of Biology, and.,the BIOSS Centre for Biological Signalling Studies, University of Freiburg, 79104 Freiburg, Germany
| | - Bettina Knapp
- the Institute of Biology II, Biochemistry: Functional Proteomics, Faculty of Biology, and
| | - Ekaterina Eimer
- From the Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine.,the Faculty of Biology
| | - Bettina Warscheid
- the Institute of Biology II, Biochemistry: Functional Proteomics, Faculty of Biology, and.,the BIOSS Centre for Biological Signalling Studies, University of Freiburg, 79104 Freiburg, Germany
| | - Matthias Müller
- From the Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine,
| | - Julia Fröbel
- From the Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine
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7
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Abstract
The general secretory pathway (Sec) and twin-arginine translocase (Tat) operate in parallel to export proteins across the cytoplasmic membrane of prokaryotes and the thylakoid membrane of plant chloroplasts. Substrates are targeted to their respective machineries by N-terminal signal peptides that share a tripartite organization; however, Tat signal peptides harbor a conserved and almost invariant arginine pair that is critical for efficient targeting to the Tat machinery. Tat signal peptides interact with a membrane-bound receptor complex comprised of TatB and TatC components, with TatC containing the twin-arginine recognition site. Here, we isolated suppressors in the signal peptide of the Tat substrate, SufI, that restored Tat transport in the presence of inactivating substitutions in the TatC twin-arginine binding site. These suppressors increased signal peptide hydrophobicity, and copurification experiments indicated that they restored binding to the variant TatBC complex. The hydrophobic suppressors could also act in cis to suppress substitutions at the signal peptide twin-arginine motif that normally prevent targeting to the Tat pathway. Highly hydrophobic variants of the SufI signal peptide containing four leucine substitutions retained the ability to interact with the Tat system. The hydrophobic signal peptides of two Sec substrates, DsbA and OmpA, containing twin lysine residues, were shown to mediate export by the Tat pathway and to copurify with TatBC. These findings indicate that there is unprecedented overlap between Sec and Tat signal peptides and that neither the signal peptide twin-arginine motif nor the TatC twin-arginine recognition site is an essential mechanistic feature for operation of the Tat pathway.IMPORTANCE Protein export is an essential process in all prokaryotes. The Sec and Tat export pathways operate in parallel, with the Sec machinery transporting unstructured precursors and the Tat pathway transporting folded proteins. Proteins are targeted to the Tat pathway by N-terminal signal peptides that contain an almost invariant twin-arginine motif. Here, we make the surprising discovery that the twin arginines are not essential for recognition of substrates by the Tat machinery and that this requirement can be bypassed by increasing the signal peptide hydrophobicity. We further show that signal peptides of bona fide Sec substrates can also mediate transport by the Tat pathway. Our findings suggest that key features of the Tat targeting mechanism have evolved to prevent mistargeting of substrates to the Sec pathway rather than being a critical requirement for function of the Tat pathway.
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8
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Huang Q, Alcock F, Kneuper H, Deme JC, Rollauer SE, Lea SM, Berks BC, Palmer T. A signal sequence suppressor mutant that stabilizes an assembled state of the twin arginine translocase. Proc Natl Acad Sci U S A 2017; 114:E1958-E1967. [PMID: 28223511 PMCID: PMC5347605 DOI: 10.1073/pnas.1615056114] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The twin-arginine protein translocation (Tat) system mediates transport of folded proteins across the cytoplasmic membrane of bacteria and the thylakoid membrane of chloroplasts. The Tat system of Escherichia coli is made up of TatA, TatB, and TatC components. TatBC comprise the substrate receptor complex, and active Tat translocases are formed by the substrate-induced association of TatA oligomers with this receptor. Proteins are targeted to TatBC by signal peptides containing an essential pair of arginine residues. We isolated substitutions, locating to the transmembrane helix of TatB that restored transport activity to Tat signal peptides with inactivating twin arginine substitutions. A subset of these variants also suppressed inactivating substitutions in the signal peptide binding site on TatC. The suppressors did not function by restoring detectable signal peptide binding to the TatBC complex. Instead, site-specific cross-linking experiments indicate that the suppressor substitutions induce conformational change in the complex and movement of the TatB subunit. The TatB F13Y substitution was associated with the strongest suppressing activity, even allowing transport of a Tat substrate lacking a signal peptide. In vivo analysis using a TatA-YFP fusion showed that the TatB F13Y substitution resulted in signal peptide-independent assembly of the Tat translocase. We conclude that Tat signal peptides play roles in substrate targeting and in triggering assembly of the active translocase.
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Affiliation(s)
- Qi Huang
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Felicity Alcock
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Holger Kneuper
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Justin C Deme
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
- Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, United Kingdom
| | - Sarah E Rollauer
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
- Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, United Kingdom
| | - Susan M Lea
- Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, United Kingdom
| | - Ben C Berks
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Tracy Palmer
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom;
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9
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Abstract
Twin-arginine protein translocation systems (Tat) translocate fully folded and co-factor-containing proteins across biological membranes. In this review, we focus on the Tat pathway of Gram-positive bacteria. The minimal Tat pathway is composed of two components, namely a TatA and TatC pair, which are often complemented with additional TatA-like proteins. We provide overviews of our current understanding of Tat pathway composition and mechanistic aspects related to Tat-dependent cargo protein translocation. This includes Tat pathway flexibility, requirements for the correct folding and incorporation of co-factors in cargo proteins and the functions of known cargo proteins. Tat pathways of several Gram-positive bacteria are discussed in detail, with emphasis on the Tat pathway of Bacillus subtilis. We discuss both shared and unique features of the different Gram-positive bacterial Tat pathways. Lastly, we highlight topics for future research on Tat, including the development of this protein transport pathway for the biotechnological secretion of high-value proteins and its potential applicability as an antimicrobial drug target in pathogens.
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Affiliation(s)
- Vivianne J Goosens
- MRC Centre for Molecular Bacteriology and Infection, Section of Microbiology, Imperial College London, London, SW7 2AZ, UK
| | - Jan Maarten van Dijl
- Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30001, 9700, RB, Groningen, The Netherlands.
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10
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A Tat ménage à trois — The role of Bacillus subtilis TatAc in twin-arginine protein translocation. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2015; 1853:2745-53. [DOI: 10.1016/j.bbamcr.2015.07.022] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Revised: 07/28/2015] [Accepted: 07/30/2015] [Indexed: 11/19/2022]
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Cléon F, Habersetzer J, Alcock F, Kneuper H, Stansfeld PJ, Basit H, Wallace MI, Berks BC, Palmer T. The TatC component of the twin-arginine protein translocase functions as an obligate oligomer. Mol Microbiol 2015; 98:111-29. [PMID: 26112072 PMCID: PMC5102672 DOI: 10.1111/mmi.13106] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/23/2015] [Indexed: 12/24/2022]
Abstract
The Tat protein export system translocates folded proteins across the bacterial cytoplasmic membrane and the plant thylakoid membrane. The Tat system in Escherichia coli is composed of TatA, TatB and TatC proteins. TatB and TatC form an oligomeric, multivalent receptor complex that binds Tat substrates, while multiple protomers of TatA assemble at substrate‐bound TatBC receptors to facilitate substrate transport. We have addressed whether oligomerisation of TatC is an absolute requirement for operation of the Tat pathway by screening for dominant negative alleles of tatC that inactivate Tat function in the presence of wild‐type tatC. Single substitutions that confer dominant negative TatC activity were localised to the periplasmic cap region. The variant TatC proteins retained the ability to interact with TatB and with a Tat substrate but were unable to support the in vivo assembly of TatA complexes. Blue‐native PAGE analysis showed that the variant TatC proteins produced smaller TatBC complexes than the wild‐type TatC protein. The substitutions did not alter disulphide crosslinking to neighbouring TatC molecules from positions in the periplasmic cap but abolished a substrate‐induced disulphide crosslink in transmembrane helix 5 of TatC. Our findings show that TatC functions as an obligate oligomer.
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Affiliation(s)
- François Cléon
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Johann Habersetzer
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Felicity Alcock
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK
| | - Holger Kneuper
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Phillip J Stansfeld
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK
| | - Hajra Basit
- Department of Chemistry, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK
| | - Mark I Wallace
- Department of Chemistry, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK
| | - Ben C Berks
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK
| | - Tracy Palmer
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
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12
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Affiliation(s)
- Ben C. Berks
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom;
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13
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Cline K. Mechanistic Aspects of Folded Protein Transport by the Twin Arginine Translocase (Tat). J Biol Chem 2015; 290:16530-8. [PMID: 25975269 DOI: 10.1074/jbc.r114.626820] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The twin arginine translocase (Tat) transports folded proteins of widely varying size across ionically tight membranes with only 2-3 components of machinery and the proton motive force. Tat operates by a cycle in which the receptor complex combines with the pore-forming component to assemble a new translocase for each substrate. Recent data on component and substrate organization in the receptor complex and on the structure of the pore complex inform models for translocase assembly and translocation. A translocation mechanism involving local transient bilayer rupture is discussed.
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Affiliation(s)
- Kenneth Cline
- From the Plant Molecular and Cellular Biology, University of Florida, Gainesville, Florida 32611
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14
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Luck AN, Evans CC, Riggs MD, Foster JM, Moorhead AR, Slatko BE, Michalski ML. Concurrent transcriptional profiling of Dirofilaria immitis and its Wolbachia endosymbiont throughout the nematode life cycle reveals coordinated gene expression. BMC Genomics 2014; 15:1041. [PMID: 25433394 PMCID: PMC4289336 DOI: 10.1186/1471-2164-15-1041] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2014] [Accepted: 11/14/2014] [Indexed: 01/24/2023] Open
Abstract
Background Dirofilaria immitis, or canine heartworm, is a filarial nematode parasite that infects dogs and other mammals worldwide. Current disease control relies on regular administration of anthelmintic preventives, however, relatively poor compliance and evidence of developing drug resistance could warrant alternative measures against D. immitis and related human filarial infections be taken. As with many other filarial nematodes, D. immitis contains Wolbachia, an obligate bacterial endosymbiont thought to be involved in providing certain critical metabolites to the nematode. Correlations between nematode and Wolbachia transcriptomes during development have not been examined. Therefore, we detailed the developmental transcriptome of both D. immitis and its Wolbachia (wDi) in order to gain a better understanding of parasite-endosymbiont interactions throughout the nematode life cycle. Results Over 215 million single-end 50 bp reads were generated from total RNA from D. immitis adult males and females, microfilariae (mf) and third and fourth-stage larvae (L3 and L4). We critically evaluated the transcriptomes of the various life cycle stages to reveal sex-biased transcriptional patterns, as well as transcriptional differences between larval stages that may be involved in larval maturation. Hierarchical clustering revealed both D. immitis and wDi transcriptional activity in the L3 stage is clearly distinct from other life cycle stages. Interestingly, a large proportion of both D. immitis and wDi genes display microfilarial-biased transcriptional patterns. Concurrent transcriptome sequencing identified potential molecular interactions between parasite and endosymbiont that are more prominent during certain life cycle stages. In support of metabolite provisioning between filarial nematodes and Wolbachia, the synthesis of the critical metabolite, heme, by wDi appears to be synchronized in a stage-specific manner (mf-specific) with the production of heme-binding proteins in D. immitis. Conclusions Our integrated transcriptomic study has highlighted interesting correlations between Wolbachia and D. immitis transcription throughout the life cycle and provided a resource that may be used for the development of novel intervention strategies, not only for the treatment and prevention of D. immitis infections, but of other closely related human parasites as well. Electronic supplementary material The online version of this article (doi:10.1186/1471-2164-15-1041) contains supplementary material, which is available to authorized users.
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Affiliation(s)
| | | | | | | | | | | | - Michelle L Michalski
- Department of Biology and Microbiology, University of Wisconsin Oshkosh, Oshkosh, WI 54901, USA.
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15
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Bozue J, Cote CK, Chance T, Kugelman J, Kern SJ, Kijek TK, Jenkins A, Mou S, Moody K, Fritz D, Robinson CG, Bell T, Worsham P. A Yersinia pestis tat mutant is attenuated in bubonic and small-aerosol pneumonic challenge models of infection but not as attenuated by intranasal challenge. PLoS One 2014; 9:e104524. [PMID: 25101850 PMCID: PMC4125294 DOI: 10.1371/journal.pone.0104524] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Accepted: 07/11/2014] [Indexed: 01/01/2023] Open
Abstract
Bacterial proteins destined for the Tat pathway are folded before crossing the inner membrane and are typically identified by an N-terminal signal peptide containing a twin arginine motif. Translocation by the Tat pathway is dependent on the products of genes which encode proteins possessing the binding site of the signal peptide and mediating the actual translocation event. In the fully virulent CO92 strain of Yersinia pestis, the tatA gene was deleted. The mutant was assayed for loss of virulence through various in vitro and in vivo assays. Deletion of the tatA gene resulted in several consequences for the mutant as compared to wild-type. Cell morphology of the mutant bacteria was altered and demonstrated a more elongated form. In addition, while cultures of the mutant strain were able to produce a biofilm, we observed a loss of adhesion of the mutant biofilm structure compared to the biofilm produced by the wild-type strain. Immuno-electron microscopy revealed a partial disruption of the F1 antigen on the surface of the mutant. The virulence of the ΔtatA mutant was assessed in various murine models of plague. The mutant was severely attenuated in the bubonic model with full virulence restored by complementation with the native gene. After small-particle aerosol challenge in a pneumonic model of infection, the mutant was also shown to be attenuated. In contrast, when mice were challenged intranasally with the mutant, very little difference in the LD50 was observed between wild-type and mutant strains. However, an increased time-to-death and delay in bacterial dissemination was observed in mice infected with the ΔtatA mutant as compared to the parent strain. Collectively, these findings demonstrate an essential role for the Tat pathway in the virulence of Y. pestis in bubonic and small-aerosol pneumonic infection but less important role for intranasal challenge.
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Affiliation(s)
- Joel Bozue
- Bacteriology Division, The United States Army of Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland, United States of America
- * E-mail:
| | - Christopher K. Cote
- Bacteriology Division, The United States Army of Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland, United States of America
| | - Taylor Chance
- Pathology Division, The United States Army of Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland, United States of America
| | - Jeffrey Kugelman
- Center for Genome Sciences, The United States Army of Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland, United States of America
| | - Steven J. Kern
- Office of Research Support, The United States Army of Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland, United States of America
| | - Todd K. Kijek
- Bacteriology Division, The United States Army of Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland, United States of America
| | - Amy Jenkins
- Bacteriology Division, The United States Army of Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland, United States of America
| | - Sherry Mou
- Bacteriology Division, The United States Army of Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland, United States of America
| | - Krishna Moody
- Bacteriology Division, The United States Army of Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland, United States of America
| | - David Fritz
- Bacteriology Division, The United States Army of Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland, United States of America
| | - Camenzind G. Robinson
- Pathology Division, The United States Army of Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland, United States of America
| | - Todd Bell
- Pathology Division, The United States Army of Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland, United States of America
| | - Patricia Worsham
- Bacteriology Division, The United States Army of Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland, United States of America
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Aldridge C, Ma X, Gerard F, Cline K. Substrate-gated docking of pore subunit Tha4 in the TatC cavity initiates Tat translocase assembly. J Cell Biol 2014; 205:51-65. [PMID: 24711501 PMCID: PMC3987133 DOI: 10.1083/jcb.201311057] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Accepted: 03/11/2014] [Indexed: 11/22/2022] Open
Abstract
The twin-arginine translocase (Tat) transports folded proteins across tightly sealed membranes. cpTatC is the core component of the thylakoid translocase and coordinates transport through interactions with the substrate signal peptide and other Tat components, notably the Tha4 pore-forming component. Here, Cys-Cys matching mapped Tha4 contact sites on cpTatC and assessed the role of signal peptide binding on Tha4 assembly with the cpTatC-Hcf106 receptor complex. Tha4 made contact with a peripheral cpTatC site in nonstimulated membranes. In the translocase, Tha4 made an additional contact within the cup-shaped cavity of cpTatC that likely seeds Tha4 polymerization to form the pore. Substrate binding triggers assembly of Tha4 onto the interior site. We provide evidence that the substrate signal peptide inserts between cpTatC subunits arranged in a manner that conceivably forms an enclosed chamber. The location of the inserted signal peptide and the Tha4-cpTatC contact data suggest a model for signal peptide-gated Tha4 entry into the chamber to form the translocase.
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Affiliation(s)
- Cassie Aldridge
- Horticultural Sciences Department and Plant Molecular and Cellular Biology, University of Florida, Gainesville, FL 32611
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17
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Berks BC, Lea SM, Stansfeld PJ. Structural biology of Tat protein transport. Curr Opin Struct Biol 2014; 27:32-7. [PMID: 24709396 DOI: 10.1016/j.sbi.2014.03.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2014] [Revised: 02/27/2014] [Accepted: 03/07/2014] [Indexed: 11/30/2022]
Abstract
The Tat protein transport system is found in the cytoplasmic membrane of prokaryotes and the thylakoid membrane of plant chloroplasts. Unusually, the Tat system translocates proteins only after they have folded. Proteins are targeted to the Tat system by specific N-terminal signal peptides. High resolution structures have recently been determined for the TatA and TatC proteins that form the Tat translocation site. These structures provide a molecular framework for understanding the mechanism of Tat transport. The interactions between TatC and the signal peptide of the substrate protein can be provisionally modelled. However, the way that TatA and TatC combine in the active translocation site remains to be definitively established.
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Affiliation(s)
- Ben C Berks
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom.
| | - Susan M Lea
- Sir William Dunn School of Pathology, South Parks Road, Oxford OX1 3RE, United Kingdom.
| | - Phillip J Stansfeld
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
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18
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Behrendt J, Brüser T. The TatBC complex of the Tat protein translocase in Escherichia coli and its transition to the substrate-bound TatABC complex. Biochemistry 2014; 53:2344-54. [PMID: 24654648 DOI: 10.1021/bi500169s] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The twin-arginine translocation (Tat) system serves to transport folded proteins across membranes of prokaryotes and plant plastids. In Escherichia coli, a complex consisting of multiple copies of TatB and TatC initiates the transport by binding the signal peptides of the Tat substrates. Using blue-native polyacrylamide gel electrophoresis, bands of TatBC-containing complexes can be detected at molecular masses of 440 and 580 kDa. We systematically analyzed the formation of Tat complexes with TatB or TatC variants that carried point mutations at selected positions. Several mutations resulted in specific disassembly patterns and alterations in the 440 kDa:580 kDa complex ratios. The 440 kDa complex contains only TatBC, whereas the 580 kDa complex consists of TatABC. Substrate binding results in a TatBC-Tat substrate complex at ~500 kDa and a TatABC-Tat substrate complex at ~600 kDa. Only the ~600 kDa complex was detected with nonrecombinant substrate levels and thus could be the physiologically most relevant species. The results suggest that some TatA is usually associated with TatBC, regardless of substrate binding.
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Affiliation(s)
- Jana Behrendt
- Institute of Microbiology, Leibniz University Hannover , Schneiderberg 50, 30167 Hannover, Germany
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19
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Simone D, Bay DC, Leach T, Turner RJ. Diversity and evolution of bacterial twin arginine translocase protein, TatC, reveals a protein secretion system that is evolving to fit its environmental niche. PLoS One 2013; 8:e78742. [PMID: 24236045 PMCID: PMC3827258 DOI: 10.1371/journal.pone.0078742] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2013] [Accepted: 09/20/2013] [Indexed: 11/18/2022] Open
Abstract
Background The twin-arginine translocation (Tat) protein export system enables the transport of fully folded proteins across a membrane. This system is composed of two integral membrane proteins belonging to TatA and TatC protein families and in some systems a third component, TatB, a homolog of TatA. TatC participates in substrate protein recognition through its interaction with a twin arginine leader peptide sequence. Methodology/Principal Findings The aim of this study was to explore TatC diversity, evolution and sequence conservation in bacteria to identify how TatC is evolving and diversifying in various bacterial phyla. Surveying bacterial genomes revealed that 77% of all species possess one or more tatC loci and half of these classes possessed only tatC and tatA genes. Phylogenetic analysis of diverse TatC homologues showed that they were primarily inherited but identified a small subset of taxonomically unrelated bacteria that exhibited evidence supporting lateral gene transfer within an ecological niche. Examination of bacilli tatCd/tatCy isoform operons identified a number of known and potentially new Tat substrate genes based on their frequent association to tatC loci. Evolutionary analysis of these Bacilli isoforms determined that TatCy was the progenitor of TatCd. A bacterial TatC consensus sequence was determined and highlighted conserved and variable regions within a three dimensional model of the Escherichia coli TatC protein. Comparative analysis between the TatC consensus sequence and Bacilli TatCd/y isoform consensus sequences revealed unique sites that may contribute to isoform substrate specificity or make TatA specific contacts. Synonymous to non-synonymous nucleotide substitution analyses of bacterial tatC homologues determined that tatC sequence variation differs dramatically between various classes and suggests TatC specialization in these species. Conclusions/Significance TatC proteins appear to be diversifying within particular bacterial classes and its specialization may be driven by the substrates it transports and the environment of its host.
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Affiliation(s)
- Domenico Simone
- Institute of Biomembranes and Bioenergetics, National Research Council, Bari, Bari, Italy
| | - Denice C. Bay
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Thorin Leach
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Raymond J. Turner
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
- * E-mail:
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20
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Goosens VJ, Monteferrante CG, van Dijl JM. The Tat system of Gram-positive bacteria. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1843:1698-706. [PMID: 24140208 DOI: 10.1016/j.bbamcr.2013.10.008] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2013] [Revised: 10/08/2013] [Accepted: 10/08/2013] [Indexed: 10/26/2022]
Abstract
The twin-arginine protein translocation (Tat) system has a unique ability to translocate folded and co-factor-containing proteins across lipid bilayers. The Tat pathway is present in bacteria, archaea and in the thylakoid membranes of chloroplasts and, depending on the organism and environmental conditions, it can be deemed important for cell survival, virulence or bioproduction. This review provides an overview of the current understanding of the Tat system with specific focus on Gram-positive bacteria. The 'universal minimal Tat system' is composed of a TatA and a TatC protein. However, this pathway is more commonly composed of two TatA-like proteins and one TatC protein. Often the TatA-like proteins have diverged to have two different functions and, in this case, the second TatA-like protein is usually referred to as TatB. The correct folding and/or incorporation of co-factors are requirements for translocation, and the known quality control mechanisms are examined in this review. A number of examples of crosstalk between the Tat system and other protein transport systems, such as the Sec-YidC translocon and signal peptidases or sheddases are also discussed. Further, an overview of specific Gram-positive bacterial Tat systems found in monoderm and diderm species is detailed. Altogether, this review highlights the unique features of Gram-positive bacterial Tat systems and pinpoints key questions that remain to be addressed in future research. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey.
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Affiliation(s)
- Vivianne J Goosens
- Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30001, 9700 RB Groningen, The Netherlands
| | - Carmine G Monteferrante
- Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30001, 9700 RB Groningen, The Netherlands
| | - Jan Maarten van Dijl
- Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30001, 9700 RB Groningen, The Netherlands.
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21
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Kudva R, Denks K, Kuhn P, Vogt A, Müller M, Koch HG. Protein translocation across the inner membrane of Gram-negative bacteria: the Sec and Tat dependent protein transport pathways. Res Microbiol 2013; 164:505-34. [DOI: 10.1016/j.resmic.2013.03.016] [Citation(s) in RCA: 122] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Accepted: 03/11/2013] [Indexed: 11/28/2022]
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22
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Ramasamy S, Abrol R, Suloway CJ, Clemons WM. The glove-like structure of the conserved membrane protein TatC provides insight into signal sequence recognition in twin-arginine translocation. Structure 2013; 21:777-88. [PMID: 23583035 PMCID: PMC3653977 DOI: 10.1016/j.str.2013.03.004] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2012] [Revised: 02/14/2013] [Accepted: 03/07/2013] [Indexed: 11/23/2022]
Abstract
In bacteria, two signal-sequence-dependent secretion pathways translocate proteins across the cytoplasmic membrane. Although the mechanism of the ubiquitous general secretory pathway is becoming well understood, that of the twin-arginine translocation pathway, responsible for translocation of folded proteins across the bilayer, is more mysterious. TatC, the largest and most conserved of three integral membrane components, provides the initial binding site of the signal sequence prior to pore assembly. Here, we present two crystal structures of TatC from the thermophilic bacteria Aquifex aeolicus at 4.0 Å and 6.8 Å resolution. The membrane architecture of TatC includes a glove-shaped structure with a lipid-exposed pocket predicted by molecular dynamics to distort the membrane. Correlating the biochemical literature to these results suggests that the signal sequence binds in this pocket, leading to structural changes that facilitate higher order assemblies.
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Affiliation(s)
| | - Ravinder Abrol
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Christian J.M. Suloway
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - William M. Clemons
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
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23
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Ma X, Cline K. Mapping the signal peptide binding and oligomer contact sites of the core subunit of the pea twin arginine protein translocase. THE PLANT CELL 2013; 25:999-1015. [PMID: 23512851 PMCID: PMC3634702 DOI: 10.1105/tpc.112.107409] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2012] [Revised: 02/08/2013] [Accepted: 02/19/2013] [Indexed: 05/17/2023]
Abstract
Twin arginine translocation (Tat) systems of thylakoid and bacterial membranes transport folded proteins using the proton gradient as the sole energy source. Tat substrates have hydrophobic signal peptides with an essential twin arginine (RR) recognition motif. The multispanning cpTatC plays a central role in Tat operation: It binds the signal peptide, directs translocase assembly, and may facilitate translocation. An in vitro assay with pea (Pisum sativum) chloroplasts was developed to conduct mutagenesis and analysis of cpTatC functions. Ala scanning mutagenesis identified mutants defective in substrate binding and receptor complex assembly. Mutations in the N terminus (S1) and first stromal loop (S2) caused specific defects in signal peptide recognition. Cys matching between substrate and imported cpTatC confirmed that S1 and S2 directly and specifically bind the RR proximal region of the signal peptide. Mutations in four lumen-proximal regions of cpTatC were defective in receptor complex assembly. Copurification and Cys matching analyses suggest that several of the lumen proximal regions may be important for cpTatC-cpTatC interactions. Surprisingly, RR binding domains of adjacent cpTatCs directed strong cpTatC-cpTatC cross-linking. This suggests clustering of binding sites on the multivalent receptor complex and explains the ability of Tat to transport cross-linked multimers. Transport of substrate proteins cross-linked to the signal peptide binding site tentatively identified mutants impaired in the translocation step.
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Affiliation(s)
- Xianyue Ma
- Horticultural Sciences Department and Plant Molecular and Cellular Biology, University of Florida, Gainesville, Florida 32611
| | - Kenneth Cline
- Horticultural Sciences Department and Plant Molecular and Cellular Biology, University of Florida, Gainesville, Florida 32611
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24
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Rollauer SE, Tarry MJ, Graham JE, Jääskeläinen M, Jäger F, Johnson S, Krehenbrink M, Liu SM, Lukey MJ, Marcoux J, McDowell MA, Rodriguez F, Roversi P, Stansfeld PJ, Robinson CV, Sansom MSP, Palmer T, Högbom M, Berks BC, Lea SM. Structure of the TatC core of the twin-arginine protein transport system. Nature 2012; 492:210-4. [PMID: 23201679 PMCID: PMC3573685 DOI: 10.1038/nature11683] [Citation(s) in RCA: 136] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Accepted: 10/18/2012] [Indexed: 12/12/2022]
Abstract
The twin-arginine translocation (Tat) pathway is one of two general protein transport systems found in the prokaryotic cytoplasmic membrane and is conserved in the thylakoid membrane of plant chloroplasts. The defining, and highly unusual, property of the Tat pathway is that it transports folded proteins, a task that must be achieved without allowing appreciable ion leakage across the membrane. The integral membrane TatC protein is the central component of the Tat pathway. TatC captures substrate proteins by binding their signal peptides. TatC then recruits TatA family proteins to form the active translocation complex. Here we report the crystal structure of TatC from the hyperthermophilic bacterium Aquifex aeolicus. This structure provides a molecular description of the core of the Tat translocation system and a framework for understanding the unique Tat transport mechanism.
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Affiliation(s)
- Sarah E Rollauer
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK
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25
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Twin-arginine translocase mutations that suppress folding quality control and permit export of misfolded substrate proteins. Proc Natl Acad Sci U S A 2012; 109:13392-7. [PMID: 22847444 DOI: 10.1073/pnas.1210140109] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The bacterial twin-arginine translocation (Tat) pathway facilitates the transport of correctly folded proteins across the tightly sealed cytoplasmic membrane. Here, we report the isolation and characterization of suppressor mutations in the Tat translocase that allow export of misfolded proteins, which form structures that are not normally tolerated by the wild-type translocase. Selection of suppressors was enabled by a genetic assay that effectively linked in vivo folding and stability of a test protein with Tat export efficiency of a selectable marker protein, namely TEM-1 β-lactamase. By using a test protein named α(3)B-a designed three-helix-bundle protein that forms collapsed, stable molten globules but lacks a uniquely folded structure-translocase mutants that rescued export of this protein were readily identified. Each mutant translocase still efficiently exported folded substrate proteins, indicating that the substrate specificity of suppressors was relaxed but not strictly altered. A subset of the suppressors could also export other misfolded proteins, such as the aggregation-prone α(3)A protein and reduced alkaline phosphatase. Importantly, the isolation of genetic suppressors that inactivate the Tat quality-control mechanism provides direct evidence for the participation of the Tat translocase in structural proofreading of substrate proteins and reveals epitopes in the translocase that are important for this process.
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26
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Kneuper H, Maldonado B, Jäger F, Krehenbrink M, Buchanan G, Keller R, Müller M, Berks BC, Palmer T. Molecular dissection of TatC defines critical regions essential for protein transport and a TatB-TatC contact site. Mol Microbiol 2012; 85:945-61. [PMID: 22742417 PMCID: PMC3712464 DOI: 10.1111/j.1365-2958.2012.08151.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The twin arginine transport (Tat) system transports folded proteins across the prokaryotic cytoplasmic membrane and the plant thylakoid membrane. TatC is the largest and most conserved component of the Tat machinery. It forms a multisubunit complex with TatB and binds the signal peptides of Tat substrates. Here we have taken a random mutagenesis approach to identify substitutions in Escherichia coli TatC that inactivate protein transport. We identify 32 individual amino acid substitutions that abolish or severely compromise TatC activity. The majority of the inactivating substitutions fall within the first two periplasmic loops of TatC. These regions are predicted to have conserved secondary structure and results of extensive amino acid insertion and deletion mutagenesis are consistent with these conserved elements being essential for TatC function. Three inactivating substitutions were identified in the fifth transmembrane helix of TatC. The inactive M205R variant could be suppressed by mutations affecting amino acids in the transmembrane helix of TatB. A physical interaction between TatC helix 5 and the TatB transmembrane helix was confirmed by the formation of a site-specific disulphide bond between TatC M205C and TatB L9C variants. This is the first molecular contact site mapped to single amino acid level between these two proteins.
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Affiliation(s)
- Holger Kneuper
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
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Fröbel J, Rose P, Müller M. Twin-arginine-dependent translocation of folded proteins. Philos Trans R Soc Lond B Biol Sci 2012; 367:1029-46. [PMID: 22411976 PMCID: PMC3297433 DOI: 10.1098/rstb.2011.0202] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Twin-arginine translocation (Tat) denotes a protein transport pathway in bacteria, archaea and plant chloroplasts, which is specific for precursor proteins harbouring a characteristic twin-arginine pair in their signal sequences. Many Tat substrates receive cofactors and fold prior to translocation. For a subset of them, proofreading chaperones coordinate maturation and membrane-targeting. Tat translocases comprise two kinds of membrane proteins, a hexahelical TatC-type protein and one or two members of the single-spanning TatA protein family, called TatA and TatB. TatC- and TatA-type proteins form homo- and hetero-oligomeric complexes. The subunits of TatABC translocases are predominantly recovered from two separate complexes, a TatBC complex that might contain some TatA, and a homomeric TatA complex. TatB and TatC coordinately recognize twin-arginine signal peptides and accommodate them in membrane-embedded binding pockets. Advanced binding of the signal sequence to the Tat translocase requires the proton-motive force (PMF) across the membranes and might involve a first recruitment of TatA. When targeted in this manner, folded twin-arginine precursors induce homo-oligomerization of TatB and TatA. Ultimately, this leads to the formation of a transmembrane protein conduit that possibly consists of a pore-like TatA structure. The translocation step again is dependent on the PMF.
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Affiliation(s)
- Julia Fröbel
- Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, Stefan-Meier-Strasse 17, 79104 Freiburg, Germany
- Faculty of Biology, University of Freiburg, Schänzle-Strasse 1, 79104 Freiburg, Germany
| | - Patrick Rose
- Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, Stefan-Meier-Strasse 17, 79104 Freiburg, Germany
- Faculty of Biology, University of Freiburg, Schänzle-Strasse 1, 79104 Freiburg, Germany
| | - Matthias Müller
- Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, Stefan-Meier-Strasse 17, 79104 Freiburg, Germany
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28
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Nuñez PA, Soria M, Farber MD. The twin-arginine translocation pathway in α-proteobacteria is functionally preserved irrespective of genomic and regulatory divergence. PLoS One 2012; 7:e33605. [PMID: 22438962 PMCID: PMC3305326 DOI: 10.1371/journal.pone.0033605] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Accepted: 02/13/2012] [Indexed: 11/19/2022] Open
Abstract
The twin-arginine translocation (Tat) pathway exports fully folded proteins out of the cytoplasm of Gram-negative and Gram-positive bacteria. Although much progress has been made in unraveling the molecular mechanism and biochemical characterization of the Tat system, little is known concerning its functionality and biological role to confer adaptive skills, symbiosis or pathogenesis in the α-proteobacteria class. A comparative genomic analysis in the α-proteobacteria class confirmed the presence of tatA, tatB, and tatC genes in almost all genomes, but significant variations in gene synteny and rearrangements were found in the order Rickettsiales with respect to the typically described operon organization. Transcription of tat genes was confirmed for Anaplasma marginale str. St. Maries and Brucella abortus 2308, two α-proteobacteria with full and partial intracellular lifestyles, respectively. The tat genes of A. marginale are scattered throughout the genome, in contrast to the more generalized operon organization. Particularly, tatA showed an approximately 20-fold increase in mRNA levels relative to tatB and tatC. We showed Tat functionality in B. abortus 2308 for the first time, and confirmed conservation of functionality in A. marginale. We present the first experimental description of the Tat system in the Anaplasmataceae and Brucellaceae families. In particular, in A. marginale Tat functionality is conserved despite operon splitting as a consequence of genome rearrangements. Further studies will be required to understand how the proper stoichiometry of the Tat protein complex and its biological role are achieved. In addition, the predicted substrates might be the evidence of role of the Tat translocation system in the transition process from a free-living to a parasitic lifestyle in these α-proteobacteria.
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Affiliation(s)
- Pablo A. Nuñez
- Instituto de Biotecnología, Instituto Nacional de Tecnología Agropecuaria (CICVyA-INTA), Buenos Aires, Argentina
| | - Marcelo Soria
- Cátedra de Microbiología Agrícola, Facultad de Agronomía, Universidad de Buenos Aires, INBA-CONICET, Buenos Aires, Argentina
| | - Marisa D. Farber
- Instituto de Biotecnología, Instituto Nacional de Tecnología Agropecuaria (CICVyA-INTA), Buenos Aires, Argentina
- * E-mail:
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29
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Koch S, Fritsch MJ, Buchanan G, Palmer T. Escherichia coli TatA and TatB proteins have N-out, C-in topology in intact cells. J Biol Chem 2012; 287:14420-31. [PMID: 22399293 DOI: 10.1074/jbc.m112.354555] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The twin arginine protein transport (Tat) system translocates folded proteins across the cytoplasmic membrane of prokaryotes and the thylakoid membrane of chloroplasts. In Escherichia coli, TatA, TatB, and TatC are essential components of the machinery. A complex of TatB and TatC acts as the substrate receptor, whereas TatA is proposed to form the Tat transport channel. TatA and TatB are related proteins that comprise an N-terminal transmembrane helix and an adjacent amphipathic helix. Previous studies addressing the topological organization of TatA have given conflicting results. In this study, we have addressed the topological arrangement of TatA and TatB in intact cells by labeling of engineered cysteine residues with the membrane-impermeable thiol reagent methoxypolyethylene glycol maleimide. Our results show that TatA and TatB share an N-out, C-in topology, with no evidence that the amphipathic helices of either protein are exposed at the periplasmic side of the membrane. We further show that the N-out, C-in topology of TatA is fixed and is not affected by the absence of other Tat components or by the overproduction of a Tat substrate. These data indicate that topological reorganization of TatA is unlikely to accompany Tat-dependent protein transport.
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Affiliation(s)
- Sabrina Koch
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
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Zoufaly S, Fröbel J, Rose P, Flecken T, Maurer C, Moser M, Müller M. Mapping precursor-binding site on TatC subunit of twin arginine-specific protein translocase by site-specific photo cross-linking. J Biol Chem 2012; 287:13430-41. [PMID: 22362773 DOI: 10.1074/jbc.m112.343798] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A number of secreted precursor proteins of bacteria, archaea, and plant chloroplasts stand out by a conserved twin arginine-containing sequence motif in their signal peptides. Many of these precursor proteins are secreted in a completely folded conformation by specific twin arginine translocation (Tat) machineries. Tat machineries are high molecular mass complexes consisting of two types of membrane proteins, a hexahelical TatC protein, and usually one or two single-spanning membrane proteins, called TatA and TatB. TatC has previously been shown to be involved in the recognition of twin arginine signal peptides. We have performed an extensive site-specific cross-linking analysis of the Escherichia coli TatC protein under resting and translocating conditions. This strategy allowed us to map the recognition site for twin arginine signal peptides to the cytosolic N-terminal region and first cytosolic loop of TatC. In addition, discrete contact sites between TatC, TatB, and TatA were revealed. We discuss a tentative model of how a twin arginine signal sequence might be accommodated in the Tat translocase.
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Affiliation(s)
- Stefan Zoufaly
- Institute of Biochemistry and Molecular Biology, Zentrum für Biochemie und Molekulare Zellforschung (ZBMZ), University of Freiburg, 79104 Freiburg, Germany
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Chang CY, Hobley L, Till R, Capeness M, Kanna M, Burtt W, Jagtap P, Aizawa SI, Sockett RE. The Bdellovibrio bacteriovorus twin-arginine transport system has roles in predatory and prey-independent growth. MICROBIOLOGY-SGM 2011; 157:3079-3093. [PMID: 21903758 DOI: 10.1099/mic.0.052449-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Bdellovibrio bacteriovorus grows in one of two ways: either (i) predatorily [in a host-dependent (HD) manner], when it invades the periplasm of another Gram-negative bacterium, exporting into the prey co-ordinated waves of soluble enzymes using the prey cell contents for growth; or (ii) in a host-independent (HI) manner, when it grows (slowly) axenically in rich media. Periplasmic invasion potentially exposes B. bacteriovorus to extremes of pH and exposes the need to scavenge electron donors from prey electron transport components by synthesis of metalloenzymes. The twin-arginine transport system (Tat) in other bacteria transports folded metalloenzymes and the B. bacteriovorus genome encodes 21 potential Tat-transported substrates and Tat transporter proteins TatA1, TatA2 and TatBC. GFP tagging of the Tat signal peptide from Bd1802, a high-potential iron-sulfur protein (HiPIP), revealed it to be exported into the prey bacterium during predatory growth. Mutagenesis showed that the B. bacteriovorus tatA2 and tatC gene products are essential for both HI and HD growth, despite the fact that they partially complement (in SDS resistance assays) the corresponding mutations in Escherichia coli where neither TatA nor TatC are essential for life. The essentiality of B. bacteriovorus TatA2 was surprising given that the B. bacteriovorus genome encodes a second tatA homologue, tatA1. Transcription of tatA1 was found to be induced upon entry to the bdelloplast, and insertional inactivation of tatA1 showed that it significantly slowed the rates of both HI and HD growth. B. bacteriovorus is one of a few bacterial species that are reliant on a functional Tat system and where deletion of a single tatA1 gene causes a significant growth defect(s), despite the presence of its tatA2 homologue.
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Affiliation(s)
- Chien-Yi Chang
- Institute of Genetics, School of Biology, University of Nottingham Medical School, Nottingham NG7 2UH, UK
| | - Laura Hobley
- Institute of Genetics, School of Biology, University of Nottingham Medical School, Nottingham NG7 2UH, UK
| | - Rob Till
- Institute of Genetics, School of Biology, University of Nottingham Medical School, Nottingham NG7 2UH, UK
| | - Michael Capeness
- Institute of Genetics, School of Biology, University of Nottingham Medical School, Nottingham NG7 2UH, UK
| | - Machi Kanna
- Prefectural University of Hiroshima, 562 Nanatsuka, Shobara, Hiroshima 727-0023, Japan
| | - William Burtt
- Institute of Genetics, School of Biology, University of Nottingham Medical School, Nottingham NG7 2UH, UK
| | - Pratik Jagtap
- Max-Planck Institute for Developmental Biology, 72076 Tübingen, Germany
| | - Shin-Ichi Aizawa
- Prefectural University of Hiroshima, 562 Nanatsuka, Shobara, Hiroshima 727-0023, Japan
| | - R Elizabeth Sockett
- Institute of Genetics, School of Biology, University of Nottingham Medical School, Nottingham NG7 2UH, UK
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Jiang X, Fares MA. Functional Diversification of the Twin-Arginine Translocation Pathway Mediates the Emergence of Novel Ecological Adaptations. Mol Biol Evol 2011; 28:3183-93. [DOI: 10.1093/molbev/msr154] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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Ciapina LP, Picchi SC, Lacroix JM, Lemos EGDM, Ödberg-Ferragut C. A putative twin-arginine translocation system in the phytopathogenic bacterium Xylella fastidiosa. Can J Microbiol 2011; 57:149-54. [PMID: 21326357 DOI: 10.1139/w10-111] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The twin-arginine translocation (Tat) pathway of the xylem-limited phytopathogenic bacterium Xylella fastidiosa strain 9a5c, responsible for citrus variegated chlorosis, was explored. The presence of tatA, tatB, and tatC in the X. fastidiosa genome together with a list of proteins harboring 2 consecutive arginines in their signal peptides suggested the presence of a Tat pathway. The functional Tat dependence of X. fastidiosa OpgD was examined. Native or mutated signal peptides were fused to the β-lactamase. Expression of fusion with intact signal peptides mediated high resistance to ampicillin in Escherichia coli tat+ but not in the E. coli tat null mutant. The replacement of the 2 arginines by 2 lysines prevented the export of β-lactamase in E. coli tat+, demonstrating that X. fastidiosa OpgD carries a signal peptide capable of engaging the E. coli Tat machinery. RT-PCR analysis revealed that the tat genes are transcribed as a single operon. tatA, tatB, and tatC genes were cloned. Complementation assays in E. coli devoid of all Tat or TatC components were unsuccessful, whereas X. fastidiosa Tat components led to a functional Tat translocase in E. coli TatB-deficient strain. Additional experiments implicated that X. fastidiosa TatB component could form a functional heterologous complex with the E. coli TatC component.
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Affiliation(s)
- Luciane Prioli Ciapina
- Unité de glycobiologie structurale et fonctionnelle, UMR USTL-CNRS 8576, IFR147, Université des sciences et technologies de Lille, Bâtiment C9, 59655 Villeneuve d'Ascq Cedex, France
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Reynolds MM, Bogomolnaya L, Guo J, Aldrich L, Bokhari D, Santiviago CA, McClelland M, Andrews-Polymenis H. Abrogation of the twin arginine transport system in Salmonella enterica serovar Typhimurium leads to colonization defects during infection. PLoS One 2011; 6:e15800. [PMID: 21298091 PMCID: PMC3027627 DOI: 10.1371/journal.pone.0015800] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Accepted: 11/24/2010] [Indexed: 11/18/2022] Open
Abstract
TatC (STM3975) is a highly conserved component of the Twin Arginine Transport (Tat) systems that is required for transport of folded proteins across the inner membrane in gram-negative bacteria. We previously identified a ΔtatC mutant as defective in competitive infections with wild type ATCC14028 during systemic infection of Salmonella-susceptible BALB/c mice. Here we confirm these results and show that the ΔtatC mutant is internalized poorly by cultured J774-A.1 mouse macrophages a phenotype that may be related to the systemic infection defect. This mutant is also defective for short-term intestinal and systemic colonization after oral infection of BALB/c mice and is shed in reduced numbers in feces from orally infected Salmonella-resistant (CBA/J) mice. We show that the ΔtatC mutant is highly sensitive to bile acids perhaps resulting in the defect in intestinal infection that we observe. Finally, the ΔtatC mutant has an unusual combination of motility phenotypes in Salmonella; it is severely defective for swimming motility but is able to swarm well. The ΔtatC mutant has a lower amount of flagellin on the bacterial surface during swimming motility but normal levels under swarming conditions.
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Affiliation(s)
- M. Megan Reynolds
- Department of Microbial and Molecular Pathogenesis, College of Medicine, Texas A & M University System Health Science Center, College Station, Texas, United States of America
| | - Lydia Bogomolnaya
- Department of Microbial and Molecular Pathogenesis, College of Medicine, Texas A & M University System Health Science Center, College Station, Texas, United States of America
| | - Jinbai Guo
- Department of Microbial and Molecular Pathogenesis, College of Medicine, Texas A & M University System Health Science Center, College Station, Texas, United States of America
| | - Lindsay Aldrich
- Department of Microbial and Molecular Pathogenesis, College of Medicine, Texas A & M University System Health Science Center, College Station, Texas, United States of America
| | - Danial Bokhari
- Department of Microbial and Molecular Pathogenesis, College of Medicine, Texas A & M University System Health Science Center, College Station, Texas, United States of America
| | - Carlos A. Santiviago
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Santiago, Chile
| | - Michael McClelland
- Vaccine Research Institute of San Diego, San Diego, California, United States of America
- Department of Pathology and Laboratory Medicine, College of Health Sciences, University of California Irvine, Irvine, California, United States of America
| | - Helene Andrews-Polymenis
- Department of Microbial and Molecular Pathogenesis, College of Medicine, Texas A & M University System Health Science Center, College Station, Texas, United States of America
- * E-mail:
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Maldonado B, Kneuper H, Buchanan G, Hatzixanthis K, Sargent F, Berks BC, Palmer T. Characterisation of the membrane-extrinsic domain of the TatB component of the twin arginine protein translocase. FEBS Lett 2011; 585:478-84. [DOI: 10.1016/j.febslet.2011.01.016] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2010] [Revised: 12/21/2010] [Accepted: 01/03/2011] [Indexed: 11/30/2022]
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Maldonado B, Buchanan G, Müller M, Berks BC, Palmer T. Genetic Evidence for a TatC Dimer at the Core of the Escherichia coli Twin Arginine (Tat) Protein Translocase. J Mol Microbiol Biotechnol 2011; 20:168-75. [DOI: 10.1159/000329076] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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37
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Abstract
Proteins that reside partially or completely outside the bacterial cytoplasm require specialized pathways to facilitate their localization. Globular proteins that function in the periplasm must be translocated across the hydrophobic barrier of the inner membrane. While the Sec pathway transports proteins in a predominantly unfolded conformation, the Tat pathway exports folded protein substrates. Protein transport by the Tat machinery is powered solely by the transmembrane proton gradient, and there is no requirement for nucleotide triphosphate hydrolysis. Proteins are targeted to the Tat machinery by N-terminal signal peptides that contain a consensus twin arginine motif. In Escherichia coli and Salmonella there are approximately thirty proteins with twin arginine signal peptides that are transported by the Tat pathway. The majority of these bind complex redox cofactors such as iron sulfur clusters or the molybdopterin cofactor. Here we describe what is known about Tat substrates in E. coli and Salmonella, the function and mechanism of Tat protein export, and how the cofactor insertion step is coordinated to ensure that only correctly assembled substrates are targeted to the Tat machinery.
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Effects of altered TatC proteins on protein secretion efficiency via the twin-arginine translocation pathway of Bacillus subtilis. Microbiology (Reading) 2009; 155:1776-1785. [DOI: 10.1099/mic.0.027987-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Protein translocation via the Tat machinery in thylakoids and bacteria occurs through a cooperation between the TatA, TatB and TatC subunits, of which the TatC protein forms the initial Tat substrate-binding site. The Bacillus subtilis Tat machinery lacks TatB and comprises two separate TatAC complexes with distinct substrate specificities: PhoD is secreted by the TatAdCd complex, whereas YwbN is secreted by the TatAyCy complex. To study the role of the Gram-positive TatC proteins in Tat-dependent protein secretion efficiency, we applied several genetic engineering approaches to modify and analyse the B. subtilis TatCd and TatCy proteins. Cytoplasmic and transmembrane domain exchange between TatCd and TatCy resulted in stable chimeric proteins that were unable to secrete both known substrates of the B. subtilis Tat system. Site-directed mutagenesis of conserved residues in the N-terminal part of both TatC proteins revealed significant differences in the degree of importance of these residues between TatCd, TatCy and Escherichia coli TatC. In addition, two small C-terminal deletions in TatCy completely abolished YwbN translocation, indicating that this terminus is essential for Tat translocation activity. Important differences from previous observations for E. coli TatC and implications for substrate binding and translocation are discussed.
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Martin JR, Harwood JH, McCaffery MW, Fernandez DE, Cline KC. Localization and integration of thylakoid protein translocase subunit cpTatC. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2009; 58:831-42. [PMID: 19207210 PMCID: PMC2787251 DOI: 10.1111/j.1365-313x.2009.03816.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Thylakoid membranes have a unique complement of proteins, most of which are nuclear encoded synthesized in the cytosol, imported into the stroma and translocated into thylakoid membranes by specific thylakoid translocases. Known thylakoid translocases contain core multi-spanning, membrane-integrated subunits that are also nuclear-encoded and imported into chloroplasts before being integrated into thylakoid membranes. Thylakoid translocases play a central role in determining the composition of thylakoids, yet the manner by which the core translocase subunits are integrated into the membrane is not known. We used biochemical and genetic approaches to investigate the integration of the core subunit of the chloroplast Tat translocase, cpTatC, into thylakoid membranes. In vitro import assays show that cpTatC correctly localizes to thylakoids if imported into intact chloroplasts, but that it does not integrate into isolated thylakoids. In vitro transit peptide processing and chimeric precursor import experiments suggest that cpTatC possesses a stroma-targeting transit peptide. Import time-course and chase assays confirmed that cpTatC targets to thylakoids via a stromal intermediate, suggesting that it might integrate through one of the known thylakoid translocation pathways. However, chemical inhibitors to the cpSecA-cpSecY and cpTat pathways did not impede cpTatC localization to thylakoids when used in import assays. Analysis of membranes isolated from Arabidopsis thaliana mutants lacking cpSecY or Alb3 showed that neither is necessary for cpTatC membrane integration or assembly into the cpTat receptor complex. These data suggest the existence of another translocase, possibly one dedicated to the integration of chloroplast translocases.
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Affiliation(s)
- Jonathan R. Martin
- Horticultural Sciences Department and Plant Molecular and Cellular Biology, University of Florida, Gainesville FL, USA
| | - Jessica H. Harwood
- Department of Botany, University of Wisconsin-Madison, 430 Lincoln Drive, Madison, WI 53706-1381, USA
| | - Michael W. McCaffery
- Horticultural Sciences Department and Plant Molecular and Cellular Biology, University of Florida, Gainesville FL, USA
| | - Donna E. Fernandez
- Department of Botany, University of Wisconsin-Madison, 430 Lincoln Drive, Madison, WI 53706-1381, USA
| | - Kenneth C. Cline
- Horticultural Sciences Department and Plant Molecular and Cellular Biology, University of Florida, Gainesville FL, USA
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Stevens CM, Winstone TML, Turner RJ, Paetzel M. Structural analysis of a monomeric form of the twin-arginine leader peptide binding chaperone Escherichia coli DmsD. J Mol Biol 2009; 389:124-33. [PMID: 19361518 DOI: 10.1016/j.jmb.2009.03.069] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2009] [Revised: 03/27/2009] [Accepted: 03/31/2009] [Indexed: 11/20/2022]
Abstract
The redox enzyme maturation proteins play an essential role in the proofreading and membrane targeting of protein substrates to the twin-arginine translocase. Functionally, the most thoroughly characterized redox enzyme maturation protein to date is Escherichia coli DmsD (EcDmsD). Herein, we present the X-ray crystal structure of the monomeric form of the EcDmsD refined to 2.0 A resolution, with clear electron density present for each of its 204 amino acid residues. The structural data presented here complement the biochemical data previously generated regarding the function of these twin-arginine translocase leader peptide binding chaperone proteins. Docking and molecular dynamics simulation experiments were used to provide a proposed model for how this chaperone is able to recognize the leader peptide of its substrate DmsA. The interactions observed in the model are in agreement with previous biochemical data and suggest intimate interactions between the conserved twin-arginine motif of the leader peptide of E. coli DmsA and the most conserved regions on the surface of EcDmsD.
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Affiliation(s)
- Charles M Stevens
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada
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Warren G, Oates J, Robinson C, Dixon AM. Contributions of the transmembrane domain and a key acidic motif to assembly and function of the TatA complex. J Mol Biol 2009; 388:122-32. [PMID: 19268473 DOI: 10.1016/j.jmb.2009.02.060] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2008] [Revised: 02/09/2009] [Accepted: 02/25/2009] [Indexed: 10/21/2022]
Abstract
The twin-arginine translocase (Tat) pathway transports folded proteins across bacterial and thylakoid membranes. In Escherichia coli, a membrane-bound TatA complex, which oligomerizes to form complexes of less than 100 to more than 500 kDa, is considered essential for translocation. We have studied the contributions of various TatA domains to the assembly and function of this heterogeneous TatA complex. The TOXCAT assay was used to analyze the potential contribution of the TatA transmembrane (TM) domain. We observed relatively weak interactions between TatA TM domains, suggesting that the TM domain is not the sole driving force behind oligomerization. A potential hydrogen-bonding role for a TM domain glutamine was also investigated, and it was found that mutation blocks transport at low expression levels, while assembly is unaffected at higher expression levels. Analysis of truncated TatA proteins instead highlighted an acidic motif directly following the TatA amphipathic helix. Mutating these negatively charged residues to apolar uncharged residues completely blocks activity, even at high levels of TatA, and appears to disrupt ordered complex formation.
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Affiliation(s)
- Gemma Warren
- MOAC Doctoral Training Centre, University of Warwick, Coventry CV4 7AL, UK
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Buchanan G, Maillard J, Nabuurs SB, Richardson DJ, Palmer T, Sargent F. Features of a twin-arginine signal peptide required for recognition by a Tat proofreading chaperone. FEBS Lett 2008; 582:3979-84. [DOI: 10.1016/j.febslet.2008.10.049] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2008] [Revised: 10/17/2008] [Accepted: 10/20/2008] [Indexed: 10/21/2022]
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Escherichia coli tat mutant strains are able to transport maltose in the absence of an active malE gene. Arch Microbiol 2008; 189:597-604. [PMID: 18385983 DOI: 10.1007/s00203-008-0356-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2007] [Revised: 01/23/2008] [Accepted: 02/13/2008] [Indexed: 10/22/2022]
Abstract
The twin-arginine transport (Tat) system is a prokaryotic protein transport system. Escherichia coli mutants in this pathway show a defect in cell separation during cell division, resulting in destabilization and permeability of the outer membrane. Maltose uptake is catalysed by a membrane-bound transporter of the ATP binding cassette (ABC) superfamily, where MalE is the essential periplasmic binding protein component. Here, we report that tat mutants are unexpectedly able to transport maltose in the absence of malE. This observation is specific to the MalE component since co-inactivation of malF, which encodes one of the channel components of the transporter, completely abolishes maltose transport even when the Tat system is inactivated. Genetic repair of the outer membrane leaky phenotype of the tat mutant strain re-established the absolute requirement for MalE in maltose uptake. In addition, we demonstrate that phenotypic repair of the outer membrane defect of the tat strain can also be achieved chemically by the inclusion of high concentrations of calcium or magnesium in the growth medium.
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The twin-arginine transport system: moving folded proteins across membranes. Biochem Soc Trans 2008; 35:835-47. [PMID: 17956229 DOI: 10.1042/bst0350835] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The Tat (twin-arginine transport) pathway is a protein-targeting system dedicated to the transmembrane translocation of fully folded proteins. This system is highly prevalent in the cytoplasmic membranes of bacteria and archaea, and is also found in the thylakoid membranes of plant chloroplasts and possibly also in the inner membrane of plant mitochondria. Proteins are targeted to a membrane-embedded Tat translocase by specialized N-terminal twin-arginine signal peptides bearing an SRRXFLK amino acid motif. The genes encoding components of the Tat translocase were discovered approx. 10 years ago, and, since then, research in this area has expanded on a global scale. In this review, the key discoveries in this field are summarized, and recent studies of bacterial twin-arginine signal-peptide-binding proteins are discussed.
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Strauch EM, Georgiou G. Escherichia coli tatC mutations that suppress defective twin-arginine transporter signal peptides. J Mol Biol 2007; 374:283-91. [PMID: 17936785 DOI: 10.1016/j.jmb.2007.09.050] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2007] [Revised: 09/18/2007] [Accepted: 09/18/2007] [Indexed: 10/22/2022]
Abstract
In vitro studies have suggested that the TatBC complex serves as the receptor for signal peptides targeted for export via the twin-arginine translocation (Tat) pathway. Substitution of the hallmark twin-arginine dipeptide with two lysines abrogates export of physiological substrates in all organisms. We report the isolation and characterization of suppressor mutations that allow export of an ssTor(KK)-GFP-SsrA tripartite fusion. We identified two amino acid suppressor mutations in the first cytoplasmic loop of TatC. In addition, two other amino acids in the first cytoplasmic loop exhibit epistatic suppression. Surprisingly, we also identified a suppressor mutation predicted to lie within the second periplasmic loop of TatC, a region that is not expected to interact directly with the signal peptide. The suppressor mutations allowed export of the native Esherichia coli Tat substrate trimethylamine N-oxide reductase with a twin-lysine substitution in its signal sequence. The cytoplasmic suppressor mutations conferred SDS sensitivity and partial filamentation, indicating that Tat export of authentic substrates was impaired.
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Affiliation(s)
- Eva-Maria Strauch
- Department of Chemistry and Biochemistry, University of Texas, Austin, TX 78712, USA
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Sec- and Tat-mediated protein secretion across the bacterial cytoplasmic membrane--distinct translocases and mechanisms. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1778:1735-56. [PMID: 17935691 DOI: 10.1016/j.bbamem.2007.07.015] [Citation(s) in RCA: 343] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2007] [Revised: 07/23/2007] [Accepted: 07/24/2007] [Indexed: 11/20/2022]
Abstract
In bacteria, two major pathways exist to secrete proteins across the cytoplasmic membrane. The general Secretion route, termed Sec-pathway, catalyzes the transmembrane translocation of proteins in their unfolded conformation, whereupon they fold into their native structure at the trans-side of the membrane. The Twin-arginine translocation pathway, termed Tat-pathway, catalyses the translocation of secretory proteins in their folded state. Although the targeting signals that direct secretory proteins to these pathways show a high degree of similarity, the translocation mechanisms and translocases involved are vastly different.
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47
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Orriss GL, Tarry MJ, Ize B, Sargent F, Lea SM, Palmer T, Berks BC. TatBC, TatB, and TatC form structurally autonomous units within the twin arginine protein transport system of Escherichia coli. FEBS Lett 2007; 581:4091-7. [PMID: 17686475 PMCID: PMC2517984 DOI: 10.1016/j.febslet.2007.07.044] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2007] [Revised: 07/06/2007] [Accepted: 07/19/2007] [Indexed: 11/22/2022]
Abstract
The Tat (twin arginine translocation) system transports folded proteins across bacterial and thylakoid membranes. The integral membrane proteins TatA, TatB, and TatC are the essential components of the Tat pathway in Escherichia coli. We demonstrate that formation of a stable complex between TatB and TatC does not require TatA or other Tat components. We show that the TatB and TatC proteins are each able to a form stable, defined, homomultimeric complexes. These we suggest correspond to structural subcomplexes within the parental TatBC complex. We infer that TatC forms a core to the TatBC complex on to which TatB assembles.
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Affiliation(s)
- George L. Orriss
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
| | - Michael J. Tarry
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
| | - Bérengère Ize
- Department of Molecular Microbiology, The John Innes Centre, Norwich NR4 7UH, United Kingdom
| | - Frank Sargent
- School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom
| | - Susan M. Lea
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, United Kingdom
| | - Tracy Palmer
- Department of Molecular Microbiology, The John Innes Centre, Norwich NR4 7UH, United Kingdom
| | - Ben C. Berks
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
- Corresponding author. Fax: +44 0 1865 275259.
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Greene NP, Porcelli I, Buchanan G, Hicks MG, Schermann SM, Palmer T, Berks BC. Cysteine scanning mutagenesis and disulfide mapping studies of the TatA component of the bacterial twin arginine translocase. J Biol Chem 2007; 282:23937-45. [PMID: 17565984 DOI: 10.1074/jbc.m702972200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Tat (twin arginine translocation) system transports folded proteins across the bacterial cytoplasmic membrane and the thylakoid membrane of plant chloroplasts. The integral membrane proteins TatA, TatB, and TatC are essential components of the Tat pathway. TatA forms high order oligomers and is thought to constitute the protein-translocating unit of the Tat system. Cysteine scanning mutagenesis was used to systematically investigate the functional importance of residues in the essential N-terminal transmembrane and amphipathic helices of Escherichia coli TatA. Cysteine substitutions of most residues in the amphipathic helix, including all the residues on the hydrophobic face of the helix, severely compromise Tat function. Glutamine 8 was identified as the only residue in the transmembrane helix that is critical for TatA function. The cysteine variants in the transmembrane helix were used in disulfide mapping experiments to probe the oligomeric arrangement of TatA protomers within the larger TatA complex. Residues in the center of the transmembrane helix (including residues 10-16) show a distinct pattern of cross-linking indicating that this region of the protein forms well defined interactions with other protomers. At least two interacting faces were detected. The results of our TatA studies are compared with analogous data for the homologous, but functionally distinct, TatB protein. This comparison reveals that it is only in TatA that the amphipathic helix is sensitive to amino acid substitutions. The TatA amphipathic helix may play a role in forming and controlling the path of substrate movement across the membrane.
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Affiliation(s)
- Nicholas P Greene
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU
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Yamada K, Sanzen I, Ohkura T, Okamoto A, Torii K, Hasegawa T, Ohta M. Analysis of Twin-Arginine Translocation Pathway Homologue in Staphylococcus aureus. Curr Microbiol 2007; 55:14-9. [PMID: 17551788 DOI: 10.1007/s00284-006-0461-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2006] [Accepted: 10/04/2006] [Indexed: 11/24/2022]
Abstract
Staphylococcus aureus releases a large number of exoproteins, including membrane-active proteins and toxins with superantigenic activity involved in pathogenicity. However, the export pathways of exoproteins in S. aureus have not been reported. We analyzed the function of the staphylococcal twin-arginine translocation (Tat) pathway homologue, the presence of which was recently discovered according to the genome database. The amino-acid sequences of the Tat homologues of S. aureus do not have a high similarity with those of Escherichia coli and other bacteria. Constructed tatC-deficient mutants from distinct parent strains showed the same patterns of exoproteins compared with those of parent strains on two-dementional gel electrophoresis, and the amounts of secreted staphylococcal enterotoxins and toxic shock syndrome toxin-1, of which signal peptides have some features often seen in signal sequences of Tat-dependent proteins, did not change with Western blotting analyses. Therefore, it seems that the Tat pathway does not play a major role in the secretion system of S. aureus, but other export pathways may play an important role in toxin secretion. This is the first experimental report showing the influence of the Tat pathway on the secretion of S. aureus.
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Affiliation(s)
- Keiko Yamada
- Department of Bacteriology, Graduate School of Medicine, Nagoya University, 65 Tsurumai-cho, Showa-ku, Nagoya, 466-8550, Japan
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Punginelli C, Maldonado B, Grahl S, Jack R, Alami M, Schröder J, Berks BC, Palmer T. Cysteine scanning mutagenesis and topological mapping of the Escherichia coli twin-arginine translocase TatC Component. J Bacteriol 2007; 189:5482-94. [PMID: 17545291 PMCID: PMC1951830 DOI: 10.1128/jb.00647-07] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The TatC protein is an essential component of the Escherichia coli twin-arginine (Tat) protein translocation pathway. It is a polytopic membrane protein that forms a complex with TatB, together acting as the receptor for Tat substrates. In this study we have constructed 57 individual cysteine substitutions throughout the protein. Each of the substitutions resulted in a TatC protein that was competent to support Tat-dependent protein translocation. Accessibility studies with membrane-permeant and -impermeant thiol-reactive reagents demonstrated that TatC has six transmembrane helices, rather than the four suggested by a previous study (K. Gouffi, C.-L. Santini, and L.-F. Wu, FEBS Lett. 525:65-70, 2002). Disulfide cross-linking experiments with TatC proteins containing single cysteine residues showed that each transmembrane domain of TatC was able to interact with the same domain from a neighboring TatC protein. Surprisingly, only three of these cysteine variants retained the ability to cross-link at low temperatures. These results are consistent with the likelihood that most of the disulfide cross-links are between TatC proteins in separate TatBC complexes, suggesting that TatC is located on the periphery of the complex.
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Affiliation(s)
- Claire Punginelli
- Department of Molecular Microbiology, John Innes Centre, Colney Lane, Norwich NR4 7UH, United Kingdom
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