1
|
Xu Z, Zhang T, Hu H, Liu W, Xu P, Tang H. Characterization on nicotine degradation and research on heavy metal resistance of a strain Pseudomonas sp. NBB. JOURNAL OF HAZARDOUS MATERIALS 2023; 459:132145. [PMID: 37557045 DOI: 10.1016/j.jhazmat.2023.132145] [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: 05/18/2023] [Revised: 07/05/2023] [Accepted: 07/23/2023] [Indexed: 08/11/2023]
Abstract
The remediation of polluted sites containing multiple contaminants like nicotine and heavy metals poses significant challenges, due to detrimental effects like cell death. In this study, we isolated a new strain Pseudomonas sp. NBB capable of efficiently degrading nicotine even in high level of heavy metals. It degraded nicotine through pyrrolidine pathway and displayed minimum inhibitory concentrations of 2 mM for barium, copper, and lead, and 5 mM for manganese. In the presence of 2 mM Ba2+ or Pb2+, 3 g L-1 nicotine could be completely degraded within 24 h. Moreover, under 0.5 mM Cu2+ or 5 mM Mn2+ stress, 24.13% and 72.56% of nicotine degradation were achieved in 60 h, respectively. Strain NBB tolerances metal stress by various strategies, including morphological changes, up-regulation of macromolecule transporters, cellular response to DNA damage, and down-regulation of ABC transporters. Notably, among the 153 up-regulated genes, cds_821 was identified as manganese exporter (MneA) after gene disruption and recovery experiments. This study presents a novel strain capable of efficiently degrading nicotine and displaying remarkable resistance to heavy metals. The findings of this research provide valuable insights into the potential application of nicotine bioremediation in heavy metal-contaminated areas.
Collapse
Affiliation(s)
- Zhaoyong Xu
- State Key Laboratory of Microbial Metabolism, and School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China
| | - Tingting Zhang
- China Tobacco Henan Industrial Co. Ltd., Zhengzhou 450000, People's Republic of China
| | - Haiyang Hu
- State Key Laboratory of Microbial Metabolism, and School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China.
| | - Wenzhao Liu
- China Tobacco Henan Industrial Co. Ltd., Zhengzhou 450000, People's Republic of China
| | - Ping Xu
- State Key Laboratory of Microbial Metabolism, and School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China
| | - Hongzhi Tang
- State Key Laboratory of Microbial Metabolism, and School of Life Sciences & Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China
| |
Collapse
|
2
|
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.
Collapse
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
| |
Collapse
|
3
|
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 DOI: 10.1073/pnas.1615056114] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [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.
Collapse
|
4
|
Alcock F, Stansfeld PJ, Basit H, Habersetzer J, Baker MA, Palmer T, Wallace MI, Berks BC. Assembling the Tat protein translocase. eLife 2016; 5. [PMID: 27914200 PMCID: PMC5201420 DOI: 10.7554/elife.20718] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Accepted: 11/29/2016] [Indexed: 12/18/2022] Open
Abstract
The twin-arginine protein translocation system (Tat) transports folded proteins across the bacterial cytoplasmic membrane and the thylakoid membranes of plant chloroplasts. The Tat transporter is assembled from multiple copies of the membrane proteins TatA, TatB, and TatC. We combine sequence co-evolution analysis, molecular simulations, and experimentation to define the interactions between the Tat proteins of Escherichia coli at molecular-level resolution. In the TatBC receptor complex the transmembrane helix of each TatB molecule is sandwiched between two TatC molecules, with one of the inter-subunit interfaces incorporating a functionally important cluster of interacting polar residues. Unexpectedly, we find that TatA also associates with TatC at the polar cluster site. Our data provide a structural model for assembly of the active Tat translocase in which substrate binding triggers replacement of TatB by TatA at the polar cluster site. Our work demonstrates the power of co-evolution analysis to predict protein interfaces in multi-subunit complexes. DOI:http://dx.doi.org/10.7554/eLife.20718.001
Collapse
Affiliation(s)
- Felicity Alcock
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | | | - Hajra Basit
- Department of Chemistry, University of Oxford, Oxford, United Kingdom
| | - Johann Habersetzer
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Matthew Ab Baker
- Department of Chemistry, University of Oxford, Oxford, United Kingdom
| | - Tracy Palmer
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Mark I Wallace
- Department of Chemistry, University of Oxford, Oxford, United Kingdom
| | - Ben C Berks
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| |
Collapse
|
5
|
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.
Collapse
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
| |
Collapse
|
6
|
Patel R, Smith SM, Robinson C. Protein transport by the bacterial Tat pathway. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:1620-8. [PMID: 24583120 DOI: 10.1016/j.bbamcr.2014.02.013] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Revised: 02/10/2014] [Accepted: 02/15/2014] [Indexed: 10/25/2022]
Abstract
The twin-arginine translocation (Tat) system accomplishes the remarkable feat of translocating large - even dimeric - proteins across tightly sealed energy-transducing membranes. All of the available evidence indicates that it is unique in terms of both structure and mechanism; however its very nature has hindered efforts to probe the core translocation events. At the heart of the problem is the fact that two large sub-complexes are believed to coalesce to form the active translocon, and 'capturing' this translocation event has been too difficult. Nevertheless, studies on the individual components have come a long way in recent years, and structural studies have reached the point where educated guesses can be made concerning the most interesting aspects of Tat. In this article we review these studies and the emerging ideas in this field. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey.
Collapse
Affiliation(s)
- Roshani Patel
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - Sarah M Smith
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - Colin Robinson
- Centre for Molecular Processing, School of Biosciences, University of Kent, Canterbury CT2 7NJ, United Kingdom.
| |
Collapse
|
7
|
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]
|
8
|
Transmembrane insertion of twin-arginine signal peptides is driven by TatC and regulated by TatB. Nat Commun 2013; 3:1311. [PMID: 23250441 PMCID: PMC3538955 DOI: 10.1038/ncomms2308] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2012] [Accepted: 11/15/2012] [Indexed: 12/03/2022] Open
Abstract
The twin-arginine translocation (Tat) pathway of bacteria and plant chloroplasts mediates the transmembrane transport of folded proteins, which harbour signal sequences with a conserved twin-arginine motif. Many Tat translocases comprise the three membrane proteins TatA, TatB and TatC. TatC was previously shown to be involved in recognizing twin-arginine signal peptides. Here we show that beyond recognition, TatC mediates the transmembrane insertion of a twin-arginine signal sequence, thereby translocating the signal sequence cleavage site across the bilayer. In the absence of TatB, this can lead to the removal of the signal sequence even from a translocation-incompetent substrate. Hence interaction of twin-arginine signal peptides with TatB counteracts their premature cleavage uncoupled from translocation. This capacity of TatB is not shared by the homologous TatA protein. Collectively our results suggest that TatC is an insertase for twin-arginine signal peptides and that translocation-proficient signal sequence recognition requires the concerted action of TatC and TatB. TatA, B and C act together to translocate folded proteins across bacterial and chloroplast membranes, however the precise mechanism remains unclear. Fröbel and colleagues discover that TatC has unforeseen membrane insertase activity, while TatB prevents premature cleavage before translocation.
Collapse
|
9
|
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.
Collapse
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
| |
Collapse
|
10
|
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.
Collapse
Affiliation(s)
- Holger Kneuper
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | | | | | | | | | | | | | | | | |
Collapse
|
11
|
Fritsch MJ, Krehenbrink M, Tarry MJ, Berks BC, Palmer T. Processing by rhomboid protease is required for Providencia stuartii TatA to interact with TatC and to form functional homo-oligomeric complexes. Mol Microbiol 2012; 84:1108-23. [PMID: 22591141 PMCID: PMC3712462 DOI: 10.1111/j.1365-2958.2012.08080.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [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. In Escherichia coli three membrane proteins, TatA, TatB and TatC, are essential components of the machinery. TatA from Providencia stuartii is homologous to E. coli TatA but is synthesized as an inactive pre-protein with an N-terminal extension of eight amino acids. Removal of this extension by the rhomboid protease AarA is required to activate P. stuartii TatA. Here we show that P. stuartii TatA can functionally substitute for E. coli TatA provided that the E. coli homologue of AarA, GlpG, is present. The oligomerization state of the P. stuartii TatA pro-protein was compared with that of the proteolytically activated protein and with E. coli TatA. The pro-protein still formed small homo-oligomers but cannot form large TatBC-dependent assemblies. In the absence of TatB, E. coli TatA or the processed form of P. stuartii TatA form a complex with TatC. However, this complex is not observed with the pro-form of P. stuartii TatA. Taken together our results suggest that the P. stuartii TatA pro-protein is inactive because it is unable to interact with TatC and cannot form the large TatA complexes required for transport.
Collapse
Affiliation(s)
- Maximilian J Fritsch
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | | | | | | | | |
Collapse
|
12
|
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.
Collapse
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
| |
Collapse
|
13
|
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.
Collapse
Affiliation(s)
- Stefan Zoufaly
- Institute of Biochemistry and Molecular Biology, Zentrum für Biochemie und Molekulare Zellforschung (ZBMZ), University of Freiburg, 79104 Freiburg, Germany
| | | | | | | | | | | | | |
Collapse
|
14
|
Fröbel J, Rose P, Müller M. Early contacts between substrate proteins and TatA translocase component in twin-arginine translocation. J Biol Chem 2011; 286:43679-43689. [PMID: 22041896 DOI: 10.1074/jbc.m111.292565] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Twin-arginine translocation (Tat) is a unique protein transport pathway in bacteria, archaea, and plastids. It mediates the transmembrane transport of fully folded proteins, which harbor a consensus twin-arginine motif in their signal sequences. In Gram-negative bacteria and plant chloroplasts, three membrane proteins, named TatA, TatB, and TatC, are required to enable Tat translocation. Available data suggest that TatA assembles into oligomeric pore-like structures that might function as the protein conduit across the lipid bilayer. Using site-specific photo-cross-linking, we have investigated the molecular environment of TatA under resting and translocating conditions. We find that monomeric TatA is an early interacting partner of functionally targeted Tat substrates. This interaction with TatA likely precedes translocation of Tat substrates and is influenced by the proton-motive force. It strictly depends on the presence of TatB and TatC, the latter of which is shown to make contacts with the transmembrane helix of TatA.
Collapse
Affiliation(s)
- Julia Fröbel
- Institute of Biochemistry and Molecular Biology, Zentrum für Biochemie und Molekulare Zellforschung (ZBMZ), University of Freiburg, 79104 Freiburg, Germany; Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany
| | - Patrick Rose
- Institute of Biochemistry and Molecular Biology, Zentrum für Biochemie und Molekulare Zellforschung (ZBMZ), University of Freiburg, 79104 Freiburg, Germany; Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany
| | - Matthias Müller
- Institute of Biochemistry and Molecular Biology, Zentrum für Biochemie und Molekulare Zellforschung (ZBMZ), University of Freiburg, 79104 Freiburg, Germany.
| |
Collapse
|
15
|
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
|
16
|
Maurer C, Panahandeh S, Jungkamp AC, Moser M, Müller M. TatB functions as an oligomeric binding site for folded Tat precursor proteins. Mol Biol Cell 2010; 21:4151-61. [PMID: 20926683 PMCID: PMC2993744 DOI: 10.1091/mbc.e10-07-0585] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
The TatABC subunits of the twin-arginine translocation machinery allow transport of folded proteins by an unknown mechanism. Here we show that the entire surfaces of folded Tat substrates contact TatB via both of its predicted helices. Our data suggest that TatB forms an oligomeric binding site that transiently accommodates folded Tat precursors. Twin-arginine-containing signal sequences mediate the transmembrane transport of folded proteins. The cognate twin-arginine translocation (Tat) machinery of Escherichia coli consists of the membrane proteins TatA, TatB, and TatC. Whereas Tat signal peptides are recognized by TatB and TatC, little is known about molecular contacts of the mature, folded part of Tat precursor proteins. We have placed a photo-cross-linker into Tat substrates at sites predicted to be either surface-exposed or hidden in the core of the folded proteins. On targeting of these variants to the Tat machinery of membrane vesicles, all surface-exposed sites were found in close proximity to TatB. Correspondingly, incorporation of the cross-linker into TatB revealed multiple precursor-binding sites in the predicted transmembrane and amphipathic helices of TatB. Large adducts indicative of TatB oligomers contacting one precursor molecule were also obtained. Cross-linking of Tat substrates to TatB required an intact twin-arginine signal peptide and disappeared upon transmembrane translocation. Our collective data are consistent with TatB forming an oligomeric binding site that transiently accommodates folded Tat precursors.
Collapse
Affiliation(s)
- Carlo Maurer
- Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, Stefan-Meier-Strasse 17, D-79104 Freiburg, Germany
| | | | | | | | | |
Collapse
|
17
|
Ma X, Cline K. Multiple precursor proteins bind individual Tat receptor complexes and are collectively transported. EMBO J 2010; 29:1477-88. [PMID: 20339348 PMCID: PMC2876949 DOI: 10.1038/emboj.2010.44] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2009] [Accepted: 03/03/2010] [Indexed: 11/09/2022] Open
Abstract
The thylakoid twin arginine protein translocation (Tat) system is thought to have a multivalent receptor complex with each cpTatC-Hcf106 pair constituting a signal peptide-binding unit. Conceptual models suggest that translocation of individual precursor proteins occurs upon assembly of a Tha4 oligomer with a precursor-occupied cpTatC-Hcf106. However, results reported here reveal that multiple precursor proteins bound to a single receptor complex can be transported together. Precursor proteins that contain one or two cysteine residues readily formed intermolecular disulphide bonds upon binding to the receptor complex, resulting in dimeric and tetrameric precursor proteins. Three lines of evidence indicate that all members of precursor oligomers were specifically bound to a receptor unit. Blue native-polyacrylamide gel electrophoresis analysis showed that oligomers were present on individual receptor complexes rather than bridging two or more receptor complexes. Upon energizing the membrane, the dimeric and tetrameric precursors were transported across the membrane with efficiencies comparable with that of monomeric precursors. These results imply a novel aspect of Tat systems, whereby multiple precursor-binding sites can act in concert to transport an interlinked oligo-precursor protein.
Collapse
Affiliation(s)
- Xianyue Ma
- Horticultural Sciences Department and Plant Molecular and Cellular Biology, University of Florida, Gainesville, FL, USA
| | - Kenneth Cline
- Horticultural Sciences Department and Plant Molecular and Cellular Biology, University of Florida, Gainesville, FL, USA
| |
Collapse
|
18
|
Holzapfel E, Moser M, Schiltz E, Ueda T, Betton JM, Müller M. Twin-Arginine-Dependent Translocation of SufI in the Absence of Cytosolic Helper Proteins. Biochemistry 2009; 48:5096-105. [DOI: 10.1021/bi900520d] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Eva Holzapfel
- Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, Stefan-Meier-Strasse 17, D-79104 Freiburg, Germany
| | - Michael Moser
- Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, Stefan-Meier-Strasse 17, D-79104 Freiburg, Germany
| | - Emile Schiltz
- Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, Stefan-Meier-Strasse 17, D-79104 Freiburg, Germany
- Institute of Organic Chemistry and Biochemistry, University of Freiburg, Albert-Strasse 21, D-79104 Freiburg, Germany
| | - Takuya Ueda
- Department of Medical Genome Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Chiba 277-8562, Japan
| | - Jean-Michel Betton
- Unité Biochimie Structurale, CNRS URA 2185, Institut Pasteur, 75724 Paris cedex 15, France
| | - Matthias Müller
- Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, Stefan-Meier-Strasse 17, D-79104 Freiburg, Germany
| |
Collapse
|
19
|
Panahandeh S, Maurer C, Moser M, DeLisa MP, Müller M. Following the path of a twin-arginine precursor along the TatABC translocase of Escherichia coli. J Biol Chem 2008; 283:33267-75. [PMID: 18836181 DOI: 10.1074/jbc.m804225200] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The twin-arginine translocation (Tat) machinery present in bacterial and thylakoidal membranes is able to transport fully folded proteins. Consistent with previous in vivo data, we show that the model Tat substrate TorA-PhoA is translocated by the TatABC translocase of Escherichia coli inner membrane vesicles, only if the PhoA moiety was allowed to fold by disulfide bond formation. Although even unfolded TorA-PhoA was found to physically associate with the Tat translocase of the vesicles, site-specific cross-linking revealed a perturbed interaction of the signal sequence of unfolded TorA-PhoA with the TatBC receptor site. Some of the folded TorA-PhoA precursor accumulated in a partially protease-protected membrane environment, from where it could be translocated into the lumen of the vesicles upon re-installation of an H+-gradient. Translocation arrest occurred in immediate vicinity to TatA. Consistent with a neighborhood to TatA, TorA-PhoA remained protease-resistant in the presence of detergents that are known to preserve the oligomeric structures of TatA. Moreover, entry of TorA-PhoA to the protease-protected environment strictly required the presence of TatA. Collectively, our results are consistent with some degree of quality control by TatBC and a recruitment of TatA to a folded substrate that has functionally engaged the twin-arginine translocase.
Collapse
Affiliation(s)
- Sascha Panahandeh
- Institut für Biochemie und Molekularbiologie, ZBMZ, Freiburg, Germany
| | | | | | | | | |
Collapse
|
20
|
Abstract
Photosynthetic electron transport pumps protons into the thylakoid lumen, creating an electrochemical potential called the protonmotive force (PMF). The energy of the thylakoid PMF is utilized by such machinery as the chloroplast F(0)F(1)-ATPase as well as the chloroplast Tat (cpTat) pathway (a protein transporter) to do work. The bulk phase thylakoid PMF decays rapidly after the termination of actinic illumination, and it has been well established via potentiometric measurements that there is no detectable electrical or chemical potential in the thylakoid after a brief time in the dark. Yet, we report herein that cpTat transport can occur for long periods in the dark. We show that the thylakoid PMF is actually present long after actinic illumination of the thylakoids ceases and that this energy is present in physiologically useful quantities. Consistent with previous studies, the dark-persisting thylakoid potential is not detectable by established indicators. We propose that cpTat transport in the dark is dependent on a pool of protons in the thylakoid held out of equilibrium with those in the bulk aqueous phase.
Collapse
Affiliation(s)
- Nikolai A Braun
- Department of Plant Biology, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA
| | | |
Collapse
|
21
|
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: 340] [Impact Index Per Article: 20.0] [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.
Collapse
|
22
|
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.
Collapse
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.
| |
Collapse
|
23
|
Behrendt J, Lindenstrauss U, Brüser T. The TatBC complex formation suppresses a modular TatB-multimerization inEscherichia coli. FEBS Lett 2007; 581:4085-90. [PMID: 17678896 DOI: 10.1016/j.febslet.2007.07.045] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2007] [Revised: 07/08/2007] [Accepted: 07/19/2007] [Indexed: 11/22/2022]
Abstract
Twin-arginine translocation (Tat) systems allow the translocation of folded proteins across biological membranes of most prokaryotes. In proteobacteria, a TatBC complex binds Tat substrates and initiates their translocation after recruitment of the component TatA. TatA and TatB belong to one protein family, but only TatB forms stable complexes with TatC. Here we show that TatB builds up TatA-like modular complexes in the absence of TatC. This TatB ladder ranges from about 100 to over 880 kDa with 105+/-10 kDa increments. TatC alone can form a 250 kDa complex which could be a scaffold that can recruit TatB to form defined TatBC complexes.
Collapse
Affiliation(s)
- Jana Behrendt
- Institute of Biology/Microbiology, University of Halle-Wittenberg, Kurt-Mothes-Strasse 3, D-06120 Halle, Germany
| | | | | |
Collapse
|
24
|
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.
Collapse
Affiliation(s)
- Claire Punginelli
- Department of Molecular Microbiology, John Innes Centre, Colney Lane, Norwich NR4 7UH, United Kingdom
| | | | | | | | | | | | | | | |
Collapse
|
25
|
Sargent F. Constructing the wonders of the bacterial world: biosynthesis of complex enzymes. Microbiology (Reading) 2007; 153:633-651. [PMID: 17322183 DOI: 10.1099/mic.0.2006/004762-0] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The prokaryotic cytoplasmic membrane not only maintains cell integrity and forms a barrier between the cell and its outside environment, but is also the location for essential biochemical processes. Microbial model systems provide excellent bases for the study of fundamental problems in membrane biology including signal transduction, chemotaxis, solute transport and, as will be the topic of this review, energy metabolism. Bacterial respiration requires a diverse array of complex, multi-subunit, cofactor-containing redox enzymes, many of which are embedded within, or located on the extracellular side of, the membrane. The biosynthesis of these enzymes therefore requires carefully controlled expression, assembly, targeting and transport processes. Here, focusing on the molybdenum-containing respiratory enzymes central to anaerobic respiration in Escherichia coli, recent descriptions of a chaperone-mediated 'proofreading' system involved in coordinating assembly and export of complex extracellular enzymes will be discussed. The paradigm proofreading chaperones are members of a large group of proteins known as the TorD family, and recent research in this area highlights common principles that underpin biosynthesis of both exported and non-exported respiratory enzymes.
Collapse
Affiliation(s)
- Frank Sargent
- Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
| |
Collapse
|
26
|
Cline K, Theg SM. The Sec and Tat Protein Translocation Pathways in Chloroplasts. MOLECULAR MACHINES INVOLVED IN PROTEIN TRANSPORT ACROSS CELLULAR MEMBRANES 2007. [DOI: 10.1016/s1874-6047(07)25018-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
|
27
|
McDevitt CA, Buchanan G, Sargent F, Palmer T, Berks BC. Subunit composition and in vivo substrate-binding characteristics of Escherichia coli Tat protein complexes expressed at native levels. FEBS J 2006; 273:5656-68. [PMID: 17212781 DOI: 10.1111/j.1742-4658.2006.05554.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The Tat system transports folded proteins across the bacterial cytoplasmic membrane and the thylakoid membrane of plant chloroplasts. Substrates are targeted to the Tat pathway by signal peptides containing a pair of consecutive arginine residues. The membrane proteins TatA, TatB and TatC are the essential components of this pathway in Escherichia coli. The complexes that these proteins form at native levels of expression have been investigated by the use of affinity tag-coding sequences fused to chromosomal tat genes. Distinct TatA and TatBC complexes were identified using size-exclusion chromatography and shown to have apparent molecular masses of approximately 700 and 500 kDa, respectively. Following in vivo expression, the Tat substrate protein SufI was found to copurify with the TatBC, but not the TatA, complex. This binding required the SufI signal peptide. Substitution of the twin-arginine residues in the SufI signal peptide by either twin lysine or twin alanine residues abolished export. However, both variant SufI proteins still copurified with the TatBC complex. These data show that the twin-arginine residues of the Tat consensus motif are not essential for binding of precursor to the TatBC complex but are required for the successful entry of the precursor into the transport cycle. The effect on substrate binding of single amino acid substitutions in TatC that affect Tat transport were studied using TatC variants Phe94Ala, Glu103Ala, Glu103Arg and Asp211Ala. Only variant Glu103Arg showed reduced copurification of SufI with TatBC. The transport defects associated with the other TatC variants do not, therefore, arise from an inability to bind substrate proteins.
Collapse
|
28
|
Lee PA, Orriss GL, Buchanan G, Greene NP, Bond PJ, Punginelli C, Jack RL, Sansom MSP, Berks BC, Palmer T. Cysteine-scanning mutagenesis and disulfide mapping studies of the conserved domain of the twin-arginine translocase TatB component. J Biol Chem 2006; 281:34072-85. [PMID: 16973610 DOI: 10.1074/jbc.m607295200] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cytoplasmic membrane protein TatB is an essential component of the Escherichia coli twin-arginine (Tat) protein translocation pathway. Together with the TatC component it forms a complex that functions as a membrane receptor for substrate proteins. Structural predictions suggest that TatB is anchored to the membrane via an N-terminal transmembrane alpha-helix that precedes an amphipathic alpha-helical section of the protein. From truncation analysis it is known that both these regions of the protein are essential for function. Here we construct 31 unique cysteine substitutions in the first 42 residues of TatB. Each of the substitutions results in a TatB protein that is competent to support Tat-dependent protein translocation. Oxidant-induced disulfide cross-linking shows that both the N-terminal and amphipathic helices form contacts with at least one other TatB protomer. For the transmembrane helix these contacts are localized to one face of the helix. Molecular modeling and molecular dynamics simulations provide insight into the possible structural basis of the transmembrane helix interactions. Using variants with double cysteine substitutions in the transmembrane helix, we were able to detect cross-links between up to five TatB molecules. Protein purification showed that species containing at least four cross-linked TatB molecules are found in correctly assembled TatBC complexes. Our results suggest that the transmembrane helices of TatB protomers are in the center rather than the periphery of the TatBC complex.
Collapse
Affiliation(s)
- Philip A Lee
- Department of Molecular Microbiology, John Innes Centre, Norwich NR4 7UH, United Kingdom
| | | | | | | | | | | | | | | | | | | |
Collapse
|
29
|
Sargent F, Berks BC, Palmer T. Pathfinders and trailblazers: a prokaryotic targeting system for transport of folded proteins. FEMS Microbiol Lett 2006; 254:198-207. [PMID: 16445746 DOI: 10.1111/j.1574-6968.2005.00049.x] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
The twin-arginine (Tat) protein translocase is a highly unusual protein transport machine that is dedicated to the movement of folded proteins across the bacterial cytoplasmic membrane. Proteins are targeted to the Tat pathway by means of N-terminal signal peptides harbouring a distinctive twin-arginine motif. In this minireview, we describe our current knowledge of the Tat system, paying particular attention to the function of the TatA protein and to the often overlooked step of signal peptide cleavage.
Collapse
Affiliation(s)
- Frank Sargent
- School of Biological Sciences, University of East Anglia, Norwich, UK.
| | | | | |
Collapse
|