1
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Pollet RM, Foley MH, Kumar SS, Elmore A, Jabara NT, Venkatesh S, Vasconcelos Pereira G, Martens EC, Koropatkin NM. Multiple TonB homologs are important for carbohydrate utilization by Bacteroides thetaiotaomicron. J Bacteriol 2023; 205:e0021823. [PMID: 37874167 PMCID: PMC10662123 DOI: 10.1128/jb.00218-23] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Accepted: 09/28/2023] [Indexed: 10/25/2023] Open
Abstract
IMPORTANCE The human gut microbiota, including Bacteroides, is required for the degradation of otherwise undigestible polysaccharides. The gut microbiota uses polysaccharides as an energy source, and fermentation products such as short-chain fatty acids are beneficial to the human host. This use of polysaccharides is dependent on the proper pairing of a TonB protein with polysaccharide-specific TonB-dependent transporters; however, the formation of these protein complexes is poorly understood. In this study, we examine the role of 11 predicted TonB homologs in polysaccharide uptake. We show that two proteins, TonB4 and TonB6, may be functionally redundant. This may allow for the development of drugs targeting Bacteroides species containing only a TonB4 homolog with limited impact on species encoding the redundant TonB6.
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Affiliation(s)
- Rebecca M. Pollet
- Department of Chemistry, Vassar College, Poughkeepsie, New York, USA
- Biochemistry Program, Vassar College, Poughkeepsie, New York, USA
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Matthew H. Foley
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Supriya Suresh Kumar
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Amanda Elmore
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | | | - Sameeksha Venkatesh
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | | | - Eric C. Martens
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Nicole M. Koropatkin
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA
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2
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Hubert T, Madec M, Schalk IJ. Experimental and computational methods to highlight behavioural variations in TonB-dependent transporter expression in Pseudomonas aeruginosa versus siderophore concentration. Sci Rep 2023; 13:20015. [PMID: 37974013 PMCID: PMC10654771 DOI: 10.1038/s41598-023-46585-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Accepted: 11/02/2023] [Indexed: 11/19/2023] Open
Abstract
Iron is a key nutrient for bacterial growth. The source can be either heme or siderophore-Fe complexes. Siderophores are small molecules synthesized by bacteria to scavenge iron from the bacterial environment. The pathogen Pseudomonas aeruginosa can express at least 15 different iron uptake pathways and all but one involve a TonB-dependent transporter (TBDT) for the uptake of iron across the outer membrane. Little is known about how bacteria modulate and adapt the expression of their different iron import pathways according to their environment. Here, we have developed fluorescent reporters between the promoter region of genes encoding a TBDT and the fluorescent reporter mCherry. With these constructs, we can follow the expression of TBDTs under different growth conditions. Mathematical modelling of the data obtained showed the transcription and expression of the gene encoding the TBDT PfeA to have a sigmoidal shape, whereas it was logarithmic for the TBDT gene foxA. Maximum transcription for pfeA was reached in the presence of 3 µM enterobactin, the siderophore recognized by PfeA, whereas the maximum was not reached for foxA with 100 µM nocardamine, the siderophore of FoxA.
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Affiliation(s)
- Thibaut Hubert
- CNRS, UMR7242, ESBS, University of Strasbourg, Bld Sébastien Brant, 67412, Illkirch, Strasbourg, France
- ICube Laboratory, CNRS, UMR 7357, University of Strasbourg, Bld Sébastien Brant, 67412, Illkirch, Strasbourg, France
| | - Morgan Madec
- ICube Laboratory, CNRS, UMR 7357, University of Strasbourg, Bld Sébastien Brant, 67412, Illkirch, Strasbourg, France.
| | - Isabelle J Schalk
- CNRS, UMR7242, ESBS, University of Strasbourg, Bld Sébastien Brant, 67412, Illkirch, Strasbourg, France.
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3
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Abstract
TonB-dependent transporters (TBDTs) are present in all gram-negative bacteria and mediate energy-dependent uptake of molecules that are too scarce or large to be taken up efficiently by outer membrane (OM) diffusion channels. This process requires energy that is derived from the proton motive force and delivered to TBDTs by the TonB-ExbBD motor complex in the inner membrane. Together with the need to preserve the OM permeability barrier, this has led to an extremely complex and fascinating transport mechanism for which the fundamentals, despite decades of research, are still unclear. In this review, we describe our current understanding of the transport mechanism of TBDTs, their potential role in the delivery of novel antibiotics, and the important contributions made by TBDT-associated (lipo)proteins.
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Affiliation(s)
- Augustinas Silale
- Biosciences Institute, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom; ,
| | - Bert van den Berg
- Biosciences Institute, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom; ,
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4
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Pollet RM, Foley MH, Kumar SS, Elmore A, Jabara NT, Venkatesh S, Pereira GV, Martens EC, Koropatkin NM. Multiple TonB Homologs are Important for Carbohydrate Utilization by Bacteroides thetaiotaomicron. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.07.548152. [PMID: 37461508 PMCID: PMC10350073 DOI: 10.1101/2023.07.07.548152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 07/24/2023]
Abstract
The human gut microbiota is able to degrade otherwise undigestible polysaccharides, largely through the activity of the Bacteroides. Uptake of polysaccharides into Bacteroides is controlled by TonB-dependent transporters (TBDT) whose transport is energized by an inner membrane complex composed of the proteins TonB, ExbB, and ExbD. Bacteroides thetaiotaomicron (B. theta) encodes 11 TonB homologs which are predicted to be able to contact TBDTs to facilitate transport. However, it is not clear which TonBs are important for polysaccharide uptake. Using strains in which each of the 11 predicted tonB genes are deleted, we show that TonB4 (BT2059) is important but not essential for proper growth on starch. In the absence of TonB4, we observed an increase in abundance of TonB6 (BT2762) in the membrane of B. theta, suggesting functional redundancy of these TonB proteins. Growth of the single deletion strains on pectin galactan, chondroitin sulfate, arabinan, and levan suggests a similar functional redundancy of the TonB proteins. A search for highly homologous proteins across other Bacteroides species and recent work in B. fragilis suggests that TonB4 is widely conserved and may play a common role in polysaccharide uptake. However, proteins similar to TonB6 are found only in B. theta and closely related species suggesting that the functional redundancy of TonB4 and TonB6 may be limited across the Bacteroides. This study extends our understanding of the protein network required for polysaccharide utilization in B. theta and highlights differences in TonB complexes across Bacteroides species.
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Affiliation(s)
- Rebecca M Pollet
- Department of Chemistry, Vassar College, Poughkeepsie, NY, 12604, USA
- Biochemistry Program, Vassar College, Poughkeepsie, NY, 12604, USA
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Matthew H Foley
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Supriya Suresh Kumar
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Amanda Elmore
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Nisrine T Jabara
- Biochemistry Program, Vassar College, Poughkeepsie, NY, 12604, USA
| | - Sameeksha Venkatesh
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | | | - Eric C Martens
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Nicole M Koropatkin
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
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5
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Surveying membrane landscapes: a new look at the bacterial cell surface. Nat Rev Microbiol 2023:10.1038/s41579-023-00862-w. [PMID: 36828896 DOI: 10.1038/s41579-023-00862-w] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/30/2023] [Indexed: 02/26/2023]
Abstract
Recent studies applying advanced imaging techniques are changing the way we understand bacterial cell surfaces, bringing new knowledge on everything from single-cell heterogeneity in bacterial populations to their drug sensitivity and mechanisms of antimicrobial resistance. In both Gram-positive and Gram-negative bacteria, the outermost surface of the bacterial cell is being imaged at nanoscale; as a result, topographical maps of bacterial cell surfaces can be constructed, revealing distinct zones and specific features that might uniquely identify each cell in a population. Functionally defined assembly precincts for protein insertion into the membrane have been mapped at nanoscale, and equivalent lipid-assembly precincts are suggested from discrete lipopolysaccharide patches. As we review here, particularly for Gram-negative bacteria, the applications of various modalities of nanoscale imaging are reawakening our curiosity about what is conceptually a 3D cell surface landscape: what it looks like, how it is made and how it provides resilience to respond to environmental impacts.
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6
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Lin X, Zmyslowski AM, Gagnon IA, Nakamoto RK, Sosnick TR. Development of in vivo HDX-MS with applications to a TonB-dependent transporter and other proteins. Protein Sci 2022; 31:e4402. [PMID: 36040258 PMCID: PMC9382693 DOI: 10.1002/pro.4402] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 07/09/2022] [Accepted: 07/11/2022] [Indexed: 12/02/2022]
Abstract
Hydrogen-deuterium exchange mass spectrometry (HDX-MS) is a powerful tool that monitors protein dynamics in solution. However, the reversible nature of HDX labels has largely limited the application to in vitro systems. Here, we describe a protocol for measuring HDX-MS in living Escherichia coli cells applied to BtuB, a TonB-dependent transporter found in outer membranes (OMs). BtuB is a convenient and biologically interesting system for testing in vivo HDX-MS due to its controllable HDX behavior and large structural rearrangements that occur during the B12 transport cycle. Our previous HDX-MS study in native OMs provided evidence for B12 binding and breaking of a salt bridge termed the Ionic Lock, an event that leads to the unfolding of the amino terminus. Although purified OMs provide a more native-like environment than reconstituted systems, disruption of the cell envelope during lysis perturbs the linkage between BtuB and the TonB complex that drives B12 transport. The in vivo HDX response of BtuB's plug domain (BtuBp) to B12 binding corroborates our previous in vitro findings that B12 alone is sufficient to break the Ionic Lock. In addition, we still find no evidence of B12 binding-induced unfolding in other regions of BtuBp that could enable B12 passage. Our protocol was successful in reporting on the HDX of several endogenous E. coli proteins measured in the same measurement. Our success in performing HDX in live cells opens the possibility for future HDX-MS studies in a native cellular environment. IMPORTANCE: We present a protocol for performing in vivo HDX-MS, focusing on BtuB, a protein whose native membrane environment is believed to be mechanistically important for B12 transport. The in vivo HDX-MS data corroborate the conclusions from our previous in vitro HDX-MS study of the allostery initiated by B12 binding. Our success with BtuB and other proteins opens the possibility for performing additional HDX-MS studies in a native cellular environment.
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Affiliation(s)
- Xiaoxuan Lin
- Department of Biochemistry and Molecular BiologyThe University of ChicagoChicagoIllinoisUSA
| | - Adam M. Zmyslowski
- Department of Biochemistry and Molecular BiologyThe University of ChicagoChicagoIllinoisUSA
- Present address:
Evozyne LLCChicagoIllinoisUSA
| | - Isabelle A. Gagnon
- Department of Biochemistry and Molecular BiologyThe University of ChicagoChicagoIllinoisUSA
| | - Robert K. Nakamoto
- Department of Molecular Physiology and Biological PhysicsUniversity of VirginiaCharlottesvilleVirginiaUSA
| | - Tobin R. Sosnick
- Department of Biochemistry and Molecular BiologyThe University of ChicagoChicagoIllinoisUSA
- Prizker School for Molecular EngineeringThe University of ChicagoChicagoIllinoisUSA
- Institute for Biophysical DynamicsThe University of ChicagoChicagoIllinoisUSA
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7
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Abstract
The Ton complex is a molecular motor at the inner membrane of Gram-negative bacteria that uses a proton gradient to apply forces on outer membrane (OM) proteins to permit active transport of nutrients into the periplasmic space. Recently, the structure of the ExbB–ExbD subcomplex was determined in several bacterial species, but the complete structure and stoichiometry of TonB have yet to be determined. The C-terminal end of TonB is known to cross the periplasm and interact with TonB-dependent outer membrane transport proteins with high affinity. Yet despite having significant knowledge of these transport proteins, it is not clear how the Ton motor opens a pathway across the outer membrane for nutrient import. Additionally, the mechanism by which energy is harnessed from the inner membrane subcomplex and transduced to the outer membrane via TonB is not well understood. In this review, we will discuss the gaps in the knowledge about the complete structure of the Ton motor complex and the relationship between ion flow used to generate mechanical work at the outer membrane and the nutrient transport process.
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8
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Analysis of six tonB gene homologs in Bacteroides fragilis revealed that tonB3 is essential for survival in experimental intestinal colonization and intra-abdominal infection. Infect Immun 2021; 90:e0046921. [PMID: 34662212 DOI: 10.1128/iai.00469-21] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The opportunistic, anaerobic pathogen and commensal of the human large intestinal tract, Bacteroides fragilis strain 638R, contains six predicted TonB proteins, termed TonB1-6, four ExbBs orthologs, ExbB1-4, and five ExbDs orthologs, ExbD1-5. The inner membrane TonB/ExbB/ExbD complex harvests energy from the proton motive force (Δp) and the TonB C-terminal domain interacts with and transduces energy to outer membrane TonB-dependent transporters (TBDTs). However, TonB's role in activating nearly one hundred TBDTs for nutrient acquisition in B. fragilis during intestinal colonization and extraintestinal infection has not been established. In this study, we show that growth was abolished in the ΔtonB3 mutant when heme, vitamin B12, Fe(III)-ferrichrome, starch, mucin-glycans, or N-linked glycans were used as a substrate for growth in vitro. Genetic complementation of the ΔtonB3 mutant with the tonB3 gene restored growth on these substrates. The ΔtonB1, ΔtonB2, ΔtonB4, ΔtonB5, and ΔtonB6 single mutants did not show a growth defect. This indicates that there was no functional compensation for the lack of TonB3, and it demonstrates that TonB3, alone, drives the TBDTs involved in the transport of essential nutrients. The ΔtonB3 mutant had a severe growth defect in a mouse model of intestinal colonization compared to the parent strain. This intestinal growth defect was enhanced in the ΔtonB3 ΔtonB6 double mutant strain which completely lost its ability to colonize the mouse intestinal tract compared to the parent strain. The ΔtonB1, ΔtonB2, ΔtonB4, and ΔtonB5 mutants did not significantly affect intestinal colonization. Moreover, the survival of the ΔtonB3 mutant strain was completely eradicated in a rat model of intra-abdominal infection. Taken together, these findings show that TonB3 was essential for survival in vivo. The genetic organization of tonB1, tonB2, tonB4, tonB5, and tonB6 gene orthologs indicates that they may interact with periplasmic and nonreceptor outer membrane proteins, but the physiological relevance of this has not been defined. Because anaerobic fermentation metabolism yields a lower Δp than aerobic respiration and B. fragilis has a reduced redox state in its periplasmic space - in contrast to an oxidative environment in aerobes - it remains to be determined if the diverse system of TonB/ExbB/ExbD orthologs encoded by B. fragilis have an increased sensitivity to PMF (relative to aerobic bacteria) to allow for the harvesting of energy under anaerobic conditions.
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9
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Nilaweera TD, Nyenhuis DA, Cafiso DS. Structural intermediates observed only in intact Escherichia coli indicate a mechanism for TonB-dependent transport. eLife 2021; 10:68548. [PMID: 34251336 PMCID: PMC8341980 DOI: 10.7554/elife.68548] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2021] [Accepted: 07/11/2021] [Indexed: 12/17/2022] Open
Abstract
Outer membrane TonB-dependent transporters facilitate the uptake of trace nutrients and carbohydrates in Gram-negative bacteria and are essential for pathogenic bacteria and the health of the microbiome. Despite this, their mechanism of transport is still unknown. Here, pulse electron paramagnetic resonance (EPR) measurements were made in intact cells on the Escherichia coli vitamin B12 transporter, BtuB. Substrate binding was found to alter the C-terminal region of the core and shift an extracellular substrate binding loop 2 nm toward the periplasm; moreover, this structural transition is regulated by an ionic lock that is broken upon binding of the inner membrane protein TonB. Significantly, this structural transition is not observed when BtuB is reconstituted into phospholipid bilayers. These measurements suggest an alternative to existing models of transport, and they demonstrate the importance of studying outer membrane proteins in their native environment.
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Affiliation(s)
- Thushani D Nilaweera
- Department of Chemistry and Center for Membrane Biology, University of Virginia, Charlottesville, United States
| | - David A Nyenhuis
- Department of Chemistry and Center for Membrane Biology, University of Virginia, Charlottesville, United States
| | - David S Cafiso
- Department of Chemistry and Center for Membrane Biology, University of Virginia, Charlottesville, United States
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10
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He X, Wu X, Qiao Y, Hu T, Wang D, Han X, Li CM. Electrical tension-triggered conversion of anaerobic to aerobic respiration of Shewanella putrefaciens CN32 cells while promoting biofilm growth in microbial fuel cells. Chem Commun (Camb) 2020; 56:6050-6053. [PMID: 32347873 DOI: 10.1039/d0cc01605e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A global gene expression analysis of Shewanella putrefaciens CN32 cells nearby a nanostructured microbial anode reveals an electrical tension-triggered conversion of anaerobic respiration to aerobic respiration with increased excretion of flavin electron shuttles and cytochrome C proteins, which sheds light on the role of electric tension in cell organisms.
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Affiliation(s)
- Xiu He
- Institute for Clean Energy & Advanced Materials, Faculty of Materials & Energy, Southwest University, No. 2 Tiansheng Road, Chongqing 400715, P. R. China.
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11
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Kopp DR, Postle K. The Intrinsically Disordered Region of ExbD Is Required for Signal Transduction. J Bacteriol 2020; 202:e00687-19. [PMID: 31932309 PMCID: PMC7167468 DOI: 10.1128/jb.00687-19] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2019] [Accepted: 01/03/2020] [Indexed: 12/26/2022] Open
Abstract
The TonB system actively transports vital nutrients across the unenergized outer membranes of the majority of Gram-negative bacteria. In this system, integral membrane proteins ExbB, ExbD, and TonB work together to transduce the proton motive force (PMF) of the inner membrane to customized active transporters in the outer membrane by direct and cyclic binding of TonB to the transporters. A PMF-dependent TonB-ExbD interaction is prevented by 10-residue deletions within a periplasmic disordered domain of ExbD adjacent to the cytoplasmic membrane. Here, we explored the function of the ExbD disordered domain in more detail. In vivo photo-cross-linking through sequential pBpa substitutions in the ExbD disordered domain captured five different ExbD complexes, some of which had been previously detected using in vivo formaldehyde cross-linking, a technique that lacks the residue-specific information that can be achieved through photo-cross-linking: two ExbB-ExbD heterodimers (one of which had not been detected previously), previously detected ExbD homodimers, previously detected PMF-dependent ExbD-TonB heterodimers, and for the first time, a predicted, ExbD-TonB PMF-independent interaction. The fact that multiple complexes were captured by the same pBpa substitution indicated the dynamic nature of ExbD interactions as the energy transduction cycle proceeded in vivo In this study, we also discovered that a conserved motif-V45, V47, L49, and P50-within the disordered domain was required for signal transduction to TonB and to the C-terminal domain of ExbD and was the source of motif essentiality.IMPORTANCE The TonB system is a virulence factor for Gram-negative pathogens. The mechanism by which cytoplasmic membrane proteins of the TonB system transduce an electrochemical gradient into mechanical energy is a long-standing mystery. TonB, ExbB, and ExbD primary amino acid sequences are characterized by regions of predicted intrinsic disorder, consistent with a proposed multiplicity of protein-protein contacts as TonB proceeds through an energy transduction cycle, a complex process that has yet to be recapitulated in vitro This study validates a region of intrinsic disorder near the ExbD transmembrane domain and identifies an essential conserved motif embedded within it that transduces signals to distal regions of ExbD suggested to configure TonB for productive interaction with outer membrane transporters.
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Affiliation(s)
- Dale R Kopp
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA
| | - Kathleen Postle
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA
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12
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The TonB m-PocAB System Is Required for Maintenance of Membrane Integrity and Polar Position of Flagella in Pseudomonas putida. J Bacteriol 2019; 201:JB.00303-19. [PMID: 31182498 DOI: 10.1128/jb.00303-19] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2019] [Accepted: 06/07/2019] [Indexed: 12/23/2022] Open
Abstract
TonB-ExbB-ExbD-like energy transduction systems are widespread among Gram-negative bacteria. While most species have only one copy of tonB-exbBD genes, the Pseudomonas species possess more TonB-ExbBD homologues. One of them, the TonB3-PocA-PocB complex, was recently shown to be required for polar localization of FlhF and, thus, the flagella in Pseudomonas aeruginosa Here, we show that the orthologous TonBm-PocA-PocB complex is important for polar localization of FlhF and flagella in Pseudomonas putida as well. Additionally, the system is necessary for maintaining membrane integrity, as the inactivation of the TonBm-PocAB complex results in increased membrane permeability, lowered stress tolerance, and conditional cell lysis. Interestingly, the functionality of TonBm-PocAB complex is more important for stationary than for exponentially growing bacteria. The whole-cell proteome analysis provided a likely explanation for this growth phase dependence, as extensive reprogramming was disclosed in an exponentially growing tonBm deletion strain, while only a few proteomic changes, mostly downregulation of outer membrane proteins, were determined in the stationary-phase ΔtonBm strain. We propose that this response in exponential phase, involving, inter alia, activation of AlgU and ColR regulons, can compensate for TonBm-PocAB's deficiency, while stationary-phase cells are unable to alleviate the lack of TonBm-PocAB. Our results suggest that mislocalization of flagella does not cause the membrane integrity problems; rather, the impaired membrane intactness of the TonBm-PocAB-deficient strain could be the reason for the random placement of flagella.IMPORTANCE The ubiquitous Pseudomonas species are well adapted to survive in a wide variety of environments. Their success relies on their versatile metabolic, signaling, and transport ability but also on their high intrinsic tolerance to various stress factors. This is why the study of the stress-surviving mechanisms of Pseudomonas species is of utmost importance. The stress tolerance of Pseudomonads is mainly achieved through the high barrier property of their membranes. Here, we present evidence that the TonB-ExbBD-like TonBm-PocAB system is involved in maintaining the membrane homeostasis of Pseudomonas putida, and its deficiency leads to lowered stress tolerance and conditional cell lysis.
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13
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Maki-Yonekura S, Matsuoka R, Yamashita Y, Shimizu H, Tanaka M, Iwabuki F, Yonekura K. Hexameric and pentameric complexes of the ExbBD energizer in the Ton system. eLife 2018; 7:35419. [PMID: 29661272 PMCID: PMC5903867 DOI: 10.7554/elife.35419] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 03/18/2018] [Indexed: 01/18/2023] Open
Abstract
Gram-negative bacteria import essential nutrients such as iron and vitamin B12 through outer membrane receptors. This process utilizes proton motive force harvested by the Ton system made up of three inner membrane proteins, ExbB, ExbD and TonB. ExbB and ExbD form the proton channel that energizes uptake through TonB. Recently, crystal structures suggest that the ExbB pentamer is the scaffold. Here, we present structures of hexameric complexes of ExbB and ExbD revealed by X-ray crystallography and single particle cryo-EM. Image analysis shows that hexameric and pentameric complexes coexist, with the proportion of hexamer increasing with pH. Channel current measurement and 2D crystallography support the existence and transition of the two oligomeric states in membranes. The hexameric complex consists of six ExbB subunits and three ExbD transmembrane helices enclosed within the central channel. We propose models for activation/inactivation associated with hexamer and pentamer formation and utilization of proton motive force. Many biological processes that are essential for life are powered by the flow of ions across the membranes of cells. Similar to how energy is stored in the water behind a dam, energy is also stored when the concentration of ions on one side of a biological membrane is higher than it is on the other. When these ions then flow down this concentration gradient, the energy can be harnessed to power other processes. In many bacteria, the concentration of hydrogen ions, or protons, is higher on the outside of the cell. When the protons flow down the concentration gradient, a protein complex called the Ton system in the bacteria’s inner membrane harnesses the energy to transport various compounds, including essential nutrients, across the outer membrane, which is about 20 nanometres away. Toxins, and viruses that infect bacteria, can also hijack the Ton system to gain entry into these cells. This means that the Ton system could perhaps be targeted via drugs to treat bacterial infections. Though the Ton system is important, structural information on this protein family is limited. The Ton complex is composed of three proteins – ExbB, ExbD and TonB – located in the bacteria’s inner membrane. ExbB and ExbD together form a channel for the protons and the complex made from these two proteins can be thought of as the system’s engine. Maki-Yonekura et al. wanted to understand how the ExbB / ExbD complex works, which was challenging because the complex was not well suited to any single structural biology technique. To get around this issue, a combination of two techniques called X-ray crystallography and single particle cryo-EM were used. This approached revealed that the two proteins form complexes made up of either five or six ExbB subunits with one or three ExbD subunits, respectively. It also showed that the proteins transition between the two forms in a cell’s membrane. More of the larger six-unit complex (also called a “hexamer”) formed at higher pH. This is consistent with the increased flow of protons through the channel when the local conditions inside the cell become less acidic. Based on these results, Maki-Yonekura et al. propose that some subunits in the core of the complex rotate to harness the energy from the flow of protons, and the number of subunits in the complex changes when it switches to become active or inactive. The discoveries may provide a new vision of dynamic membrane biology. Further studies are now needed to see how general this mechanism is in biology, and the new structural information could also be used to help develop more anti-bacterial drugs.
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Affiliation(s)
| | - Rei Matsuoka
- Biostructural Mechanism Laboratory, RIKEN SPring-8 Center, Sayo, Japan
| | - Yoshiki Yamashita
- Biostructural Mechanism Laboratory, RIKEN SPring-8 Center, Sayo, Japan
| | - Hirofumi Shimizu
- Department of Molecular Physiology and Biophysics, Faculty of Medical Sciences, University of Fukui, Fukui, Japan
| | - Maiko Tanaka
- Biostructural Mechanism Laboratory, RIKEN SPring-8 Center, Sayo, Japan
| | - Fumie Iwabuki
- Biostructural Mechanism Laboratory, RIKEN SPring-8 Center, Sayo, Japan
| | - Koji Yonekura
- Biostructural Mechanism Laboratory, RIKEN SPring-8 Center, Sayo, Japan
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14
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Pokorzynski ND, Thompson CC, Carabeo RA. Ironing Out the Unconventional Mechanisms of Iron Acquisition and Gene Regulation in Chlamydia. Front Cell Infect Microbiol 2017; 7:394. [PMID: 28951853 PMCID: PMC5599777 DOI: 10.3389/fcimb.2017.00394] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 08/23/2017] [Indexed: 01/19/2023] Open
Abstract
The obligate intracellular pathogen Chlamydia trachomatis, along with its close species relatives, is known to be strictly dependent upon the availability of iron. Deprivation of iron in vitro induces an aberrant morphological phenotype termed "persistence." This persistent phenotype develops in response to various immunological and nutritional insults and may contribute to the development of sub-acute Chlamydia-associated chronic diseases in susceptible populations. Given the importance of iron to Chlamydia, relatively little is understood about its acquisition and its role in gene regulation in comparison to other iron-dependent bacteria. Analysis of the genome sequences of a variety of chlamydial species hinted at the involvement of unconventional mechanisms, being that Chlamydia lack many conventional systems of iron homeostasis that are highly conserved in other bacteria. Herein we detail past and current research regarding chlamydial iron biology in an attempt to provide context to the rapid progress of the field in recent years. We aim to highlight recent discoveries and innovations that illuminate the strategies involved in chlamydial iron homeostasis, including the vesicular mode of acquiring iron from the intracellular environment, and the identification of a putative iron-dependent transcriptional regulator that is synthesized as a fusion with a ABC-type transporter subunit. These recent findings, along with the noted absence of iron-related homologs, indicate that Chlamydia have evolved atypical approaches to the problem of iron homeostasis, reinvigorating research into the iron biology of this pathogen.
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Affiliation(s)
- Nick D Pokorzynski
- School of Molecular Biosciences, College of Veterinary Medicine, Washington State UniversityPullman, WA, United States
| | - Christopher C Thompson
- Jefferiss Trust Laboratories, Faculty of Medicine, Imperial College London, St. Mary's HospitalLondon, United Kingdom
| | - Rey A Carabeo
- School of Molecular Biosciences, College of Veterinary Medicine, Washington State UniversityPullman, WA, United States
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15
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Shrivastava R, Jiang X, Chng SS. Outer membrane lipid homeostasis via retrograde phospholipid transport in Escherichia coli. Mol Microbiol 2017; 106:395-408. [PMID: 28815827 DOI: 10.1111/mmi.13772] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/14/2017] [Indexed: 01/21/2023]
Abstract
Biogenesis of the outer membrane (OM) in Gram-negative bacteria, which is essential for viability, requires the coordinated transport and assembly of proteins and lipids, including lipopolysaccharides (LPS) and phospholipids (PLs), into the membrane. While pathways for LPS and OM protein assembly are well-studied, how PLs are transported to and from the OM is not clear. Mechanisms that ensure OM stability and homeostasis are also unknown. The trans-envelope Tol-Pal complex, whose physiological role has remained elusive, is important for OM stability. Here, we establish that the Tol-Pal complex is required for PL transport and OM lipid homeostasis in Escherichia coli. Cells lacking the complex exhibit defects in lipid asymmetry and accumulate excess PLs in the OM. This imbalance in OM lipids is due to defective retrograde PL transport in the absence of a functional Tol-Pal complex. Thus, cells ensure the assembly of a stable OM by maintaining an excess flux of PLs to the OM only to return the surplus to the inner membrane. Our findings also provide insights into the mechanism by which the Tol-Pal complex may promote OM invagination during cell division.
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Affiliation(s)
- Rahul Shrivastava
- Department of Chemistry, National University of Singapore, Singapore 117543
| | - Xiang'Er Jiang
- Department of Chemistry, National University of Singapore, Singapore 117543
| | - Shu-Sin Chng
- Department of Chemistry, National University of Singapore, Singapore 117543.,Singapore Center for Environmental Life Sciences Engineering, National University of Singapore (SCELSE-NUS), Singapore 117456
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16
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Assessing Energy-Dependent Protein Conformational Changes in the TonB System. Methods Mol Biol 2017. [PMID: 28667620 DOI: 10.1007/978-1-4939-7033-9_22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Changes in conformation can alter a protein's vulnerability to proteolysis. Thus, in vivo differential proteinase sensitivity provides a means for identifying conformational changes that mark discrete states in the activity cycle of a protein. The ability to detect a specific conformational state allows for experiments to address specific protein-protein interactions and other physiological components that potentially contribute to the function of the protein. This chapter presents the application of this technique to the TonB-dependent energy transduction system of Gram-negative bacteria, a strategy that has refined our understanding of how the TonB protein is coupled to the ion electrochemical gradient of the cytoplasmic membrane.
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17
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Going Outside the TonB Box: Identification of Novel FepA-TonB Interactions In Vivo. J Bacteriol 2017; 199:JB.00649-16. [PMID: 28264993 DOI: 10.1128/jb.00649-16] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2016] [Accepted: 02/15/2017] [Indexed: 01/30/2023] Open
Abstract
In Gram-negative bacteria, the cytoplasmic membrane protein TonB transmits energy derived from proton motive force to energize transport of important nutrients through TonB-dependent transporters in the outer membrane. Each transporter consists of a beta barrel domain and a lumen-occluding cork domain containing an essential sequence called the TonB box. To date, the only identified site of transporter-TonB interaction is between the TonB box and residues ∼158 to 162 of TonB. While the mechanism of ligand transport is a mystery, a current model based on site-directed spin labeling and molecular dynamics simulations is that, following ligand binding, the otherwise-sequestered TonB box extends into the periplasm for recognition by TonB, which mediates transport by pulling or twisting the cork. In this study, we tested that hypothesis with the outer membrane transporter FepA using in vivo photo-cross-linking to explore interactions of its TonB box and determine whether additional FepA-TonB interaction sites exist. We found numerous specific sites of FepA interaction with TonB on the periplasmic face of the FepA cork in addition to the TonB box. Two residues, T32 and A33, might constitute a ligand-sensitive conformational switch. The facts that some interactions were enhanced in the absence of ligand and that other interactions did not require the TonB box argued against the current model and suggested that the transport process is more complex than originally conceived, with subtleties that might provide a mechanism for discrimination among ligand-loaded transporters. These results constitute the first study on the dynamics of TonB-gated transporter interaction with TonB in vivoIMPORTANCE The TonB system of Gram-negative bacteria has a noncanonical active transport mechanism involving signal transduction and proteins integral to both membranes. To achieve transport, the cytoplasmic membrane protein TonB physically contacts outer membrane transporters such as FepA. Only one contact between TonB and outer membrane transporters has been identified to date: the TonB box at the transporter amino terminus. The TonB box has low information content, raising the question of how TonB can discriminate among multiple different TonB-dependent transporters present in the bacterium if it is the only means of contact. Here we identified several additional sites through which FepA contacts TonB in vivo, including two neighboring residues that may explain how FepA signals to TonB that ligand has bound.
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18
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TonB-dependent ligand trapping in the BtuB transporter. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:3105-3112. [DOI: 10.1016/j.bbamem.2016.09.019] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Revised: 09/21/2016] [Accepted: 09/22/2016] [Indexed: 11/22/2022]
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19
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Liu M, Wang M, Zhu D, Wang M, Jia R, Chen S, Sun K, Yang Q, Wu Y, Chen X, Biville F, Cheng A. Investigation of TbfA in Riemerella anatipestifer using plasmid-based methods for gene over-expression and knockdown. Sci Rep 2016; 6:37159. [PMID: 27845444 PMCID: PMC5109031 DOI: 10.1038/srep37159] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 10/25/2016] [Indexed: 01/01/2023] Open
Abstract
Riemerella anatipestifer is a duck pathogen that has caused serious economic losses to the duck industry worldwide. Despite this, there are few reported studies of the physiological and pathogenic mechanisms of Riemerella anatipestifer infection. In previous study, we have shown that TonB1 and TonB2 were involved in hemin uptake. TonB family protein (TbfA) was not investigated, since knockout of this gene was not successful at that time. Here, we used a plasmid based gene over-expression and knockdown to investigate its function. First, we constructed three Escherichia-Riemerella anatipestifer shuttle vectors containing three different native Riemerella anatipestifer promoters. The shuttle plasmids were introduced into Riemerella anatipestifer ATCC11845 by conjugation at an efficiency of 5 × 10-5 antibiotic-resistant transconjugants per recipient cell. Based on the high-expression shuttle vector pLMF03, a method for gene knockdown was established. Knockdown of TbfA in Riemerella anatipestifer ATCC11845 decreased the organism's growth ability in TSB medium but did not affect its hemin utilization. In contrast, over-expression of TbfA in Riemerella anatipestifer ATCC11845ΔtonB1ΔtonB2. Significantly promoted the organism's growth in TSB medium but significantly inhibited its hemin utilization. Collectively, these findings suggest that TbfA is not involved in hemin utilization by Riemerella anatipestifer.
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Affiliation(s)
- MaFeng Liu
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Key Laboratory of Animal Disease and Human Health of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan 611130, P. R. China
| | - MengYi Wang
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Key Laboratory of Animal Disease and Human Health of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan 611130, P. R. China
| | - DeKang Zhu
- Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Key Laboratory of Animal Disease and Human Health of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan 611130, P. R. China
| | - MingShu Wang
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Key Laboratory of Animal Disease and Human Health of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan 611130, P. R. China
| | - RenYong Jia
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Key Laboratory of Animal Disease and Human Health of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan 611130, P. R. China
| | - Shun Chen
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Key Laboratory of Animal Disease and Human Health of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan 611130, P. R. China
| | - KunFeng Sun
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Key Laboratory of Animal Disease and Human Health of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan 611130, P. R. China
| | - Qiao Yang
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Key Laboratory of Animal Disease and Human Health of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan 611130, P. R. China
| | - Ying Wu
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Key Laboratory of Animal Disease and Human Health of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan 611130, P. R. China
| | - XiaoYue Chen
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Key Laboratory of Animal Disease and Human Health of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan 611130, P. R. China
| | - Francis Biville
- Unité des Infections Bactériennes Invasives, Département Infection et Epidémiologie, Institut Pasteur, Paris, France
| | - AnChun Cheng
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, Chengdu, Sichuan 611130, P.R. China.,Key Laboratory of Animal Disease and Human Health of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan 611130, P. R. China
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20
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The mechanism of force transmission at bacterial focal adhesion complexes. Nature 2016; 539:530-535. [PMID: 27749817 DOI: 10.1038/nature20121] [Citation(s) in RCA: 86] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 09/28/2016] [Indexed: 12/14/2022]
Abstract
Various rod-shaped bacteria mysteriously glide on surfaces in the absence of appendages such as flagella or pili. In the deltaproteobacterium Myxococcus xanthus, a putative gliding motility machinery (the Agl-Glt complex) localizes to so-called focal adhesion sites (FASs) that form stationary contact points with the underlying surface. Here we show that the Agl-Glt machinery contains an inner-membrane motor complex that moves intracellularly along a right-handed helical path; when the machinery becomes stationary at FASs, the motor complex powers a left-handed rotation of the cell around its long axis. At FASs, force transmission requires cyclic interactions between the molecular motor and the adhesion proteins of the outer membrane via a periplasmic interaction platform, which presumably involves contractile activity of motor components and possible interactions with peptidoglycan. Our results provide a molecular model of bacterial gliding motility.
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21
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Abstract
The rotational surveillance and energy transfer (ROSET) model of TonB action suggests a mechanism by which the electrochemical proton gradient across the Gram-negative bacterial inner membrane (IM) promotes the transport of iron through ligand-gated porins (LGP) in the outer membrane (OM). TonB associates with the IM by an N-terminal hydrophobic helix that forms a complex with ExbBD. It also contains a central extended length of rigid polypeptide that spans the periplasm and a dimeric C-terminal-ββαβ-domain (CTD) with LysM motifs that binds the peptidoglycan (PG) layer beneath the OM bilayer. The TonB CTD forms a dimer with affinity for both PG- and TonB-independent OM proteins (e.g., OmpA), localizing it near the periplasmic interface of the OM bilayer. Porins and other OM proteins associate with PG, and this general affinity allows the TonB CTD dimer to survey the periplasmic surface of the OM bilayer. Energized rotational motion of the TonB N terminus in the fluid IM bilayer promotes the lateral movement of the TonB-ExbBD complex in the IM and of the TonB CTD dimer across the inner surface of the OM. When it encounters an accessible TonB box of a (ligand-bound) LGP, the monomeric form of the CTD binds and recruits it into a 4-stranded β-sheet. Because the CTD is rotating, this binding reaction transfers kinetic energy, created by the electrochemical proton gradient across the IM, through the periplasm to the OM protein. The equilibration of the TonB C terminus between the dimeric and monomeric forms that engage in different binding reactions allows the identification of iron-loaded LGP and then the internalization of iron through their trans-outer membrane β-barrels. Hence, the ROSET model postulates a mechanism for the transfer of energy from the IM to the OM, triggering iron uptake.
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