1
|
Nemchinova M, Schuurman-Wolters GK, Whittaker JJ, Arkhipova V, Marrink SJ, Poolman B, Guskov A. Exploring the Ligand Binding and Conformational Dynamics of the Substrate-Binding Domain 1 of the ABC Transporter GlnPQ. J Phys Chem B 2024; 128:7822-7832. [PMID: 39090964 PMCID: PMC11331510 DOI: 10.1021/acs.jpcb.4c02662] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2024] [Revised: 07/21/2024] [Accepted: 07/25/2024] [Indexed: 08/04/2024]
Abstract
The adenosine triphosphate (ATP)-binding cassette (ABC) importer GlnPQ from Lactococcus lactis has two sequential covalently linked substrate-binding domains (SBDs), which capture the substrates and deliver them to the translocon. The two SBDs differ in their ligand specificities, binding affinities and the distance to the transmembrane domain; interestingly, both SBDs can bind their ligands simultaneously without affecting each other. In this work, we studied the binding of ligands to both SBDs using X-ray crystallography and molecular dynamics simulations. We report three high-resolution structures of SBD1, namely, the wild-type SBD1 with bound asparagine or arginine, and E184D SBD1 with glutamine bound. Molecular dynamics (MD) simulations provide a detailed insight into the dynamics associated with open-closed transitions of the SBDs.
Collapse
Affiliation(s)
- Mariia Nemchinova
- Groningen
Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG Groningen, The Netherlands
| | - Gea K. Schuurman-Wolters
- Groningen
Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG Groningen, The Netherlands
| | - Jacob J. Whittaker
- Groningen
Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG Groningen, The Netherlands
| | - Valentina Arkhipova
- Groningen
Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG Groningen, The Netherlands
| | - Siewert J. Marrink
- Groningen
Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG Groningen, The Netherlands
| | - Bert Poolman
- Groningen
Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG Groningen, The Netherlands
| | - Albert Guskov
- Groningen
Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG Groningen, The Netherlands
| |
Collapse
|
2
|
van den Noort M, Drougkas P, Paulino C, Poolman B. The substrate-binding domains of the osmoregulatory ABC importer OpuA transiently interact. eLife 2024; 12:RP90996. [PMID: 38695350 PMCID: PMC11065425 DOI: 10.7554/elife.90996] [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] [Indexed: 05/04/2024] Open
Abstract
Bacteria utilize various strategies to prevent internal dehydration during hypertonic stress. A common approach to countering the effects of the stress is to import compatible solutes such as glycine betaine, leading to simultaneous passive water fluxes following the osmotic gradient. OpuA from Lactococcus lactis is a type I ABC-importer that uses two substrate-binding domains (SBDs) to capture extracellular glycine betaine and deliver the substrate to the transmembrane domains for subsequent transport. OpuA senses osmotic stress via changes in the internal ionic strength and is furthermore regulated by the 2nd messenger cyclic-di-AMP. We now show, by means of solution-based single-molecule FRET and analysis with multi-parameter photon-by-photon hidden Markov modeling, that the SBDs transiently interact in an ionic strength-dependent manner. The smFRET data are in accordance with the apparent cooperativity in transport and supported by new cryo-EM data of OpuA. We propose that the physical interactions between SBDs and cooperativity in substrate delivery are part of the transport mechanism.
Collapse
Affiliation(s)
- Marco van den Noort
- Department of Biochemistry, Groningen Biomolecular Science and Biotechnology Institute, University of GroningenGroningenNetherlands
| | - Panagiotis Drougkas
- Department of Biochemistry, Groningen Biomolecular Science and Biotechnology Institute, University of GroningenGroningenNetherlands
- Biochemistry Center, Heidelberg UniversityHeidelbergGermany
| | - Cristina Paulino
- Department of Biochemistry, Groningen Biomolecular Science and Biotechnology Institute, University of GroningenGroningenNetherlands
- Biochemistry Center, Heidelberg UniversityHeidelbergGermany
| | - Bert Poolman
- Department of Biochemistry, Groningen Biomolecular Science and Biotechnology Institute, University of GroningenGroningenNetherlands
| |
Collapse
|
3
|
Ploetz E, Schuurman-Wolters GK, Zijlstra N, Jager AW, Griffith DA, Guskov A, Gouridis G, Poolman B, Cordes T. Structural and biophysical characterization of the tandem substrate-binding domains of the ABC importer GlnPQ. Open Biol 2021; 11:200406. [PMID: 33823661 PMCID: PMC8025302 DOI: 10.1098/rsob.200406] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The ATP-binding cassette transporter GlnPQ is an essential uptake system that transports glutamine, glutamic acid and asparagine in Gram-positive bacteria. It features two extra-cytoplasmic substrate-binding domains (SBDs) that are linked in tandem to the transmembrane domain of the transporter. The two SBDs differ in their ligand specificities, binding affinities and their distance to the transmembrane domain. Here, we elucidate the effects of the tandem arrangement of the domains on the biochemical, biophysical and structural properties of the protein. For this, we determined the crystal structure of the ligand-free tandem SBD1-2 protein from Lactococcus lactis in the absence of the transporter and compared the tandem to the isolated SBDs. We also used isothermal titration calorimetry to determine the ligand-binding affinity of the SBDs and single-molecule Förster resonance energy transfer (smFRET) to relate ligand binding to conformational changes in each of the domains of the tandem. We show that substrate binding and conformational changes are not notably affected by the presence of the adjoining domain in the wild-type protein, and changes only occur when the linker between the domains is shortened. In a proof-of-concept experiment, we combine smFRET with protein-induced fluorescence enhancement (PIFE–FRET) and show that a decrease in SBD linker length is observed as a linear increase in donor-brightness for SBD2 while we can still monitor the conformational states (open/closed) of SBD1. These results demonstrate the feasibility of PIFE–FRET to monitor protein–protein interactions and conformational states simultaneously.
Collapse
Affiliation(s)
- Evelyn Ploetz
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.,Department of Chemistry, Center for Nanosciences (CeNS) and Center for Integrated Proteins Science Munich (CiPSM), Ludwig Maximilians-Universität München, Butenandtstraße 11, 81377 Munich, Germany
| | - Gea K Schuurman-Wolters
- Groningen Biomolecular Science and Biotechnology Institute, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Niels Zijlstra
- Physical and Synthetic Biology, Faculty of Biology, Großhaderner Straße 2-4, Ludwig-Maximilians-Universität München, 82152 Planegg-Martinsried, Germany
| | - Amarins W Jager
- Groningen Biomolecular Science and Biotechnology Institute, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Douglas A Griffith
- Physical and Synthetic Biology, Faculty of Biology, Großhaderner Straße 2-4, Ludwig-Maximilians-Universität München, 82152 Planegg-Martinsried, Germany
| | - Albert Guskov
- Groningen Biomolecular Science and Biotechnology Institute, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.,Moscow Institute of Physics and Technology (MIPT), Institutskiy Pereulok 9, Dolgoprudny, Moscow Region 141701, Russian Federation
| | - Giorgos Gouridis
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.,Structural Biology Division, Institute of Molecular Biology and Biotechnology (IMBB-FORTH), Nikolaou Plastira 100, Heraklion, Crete, Greece
| | - Bert Poolman
- Groningen Biomolecular Science and Biotechnology Institute, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Thorben Cordes
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.,Physical and Synthetic Biology, Faculty of Biology, Großhaderner Straße 2-4, Ludwig-Maximilians-Universität München, 82152 Planegg-Martinsried, Germany
| |
Collapse
|
4
|
Kleerebezem M, Bachmann H, van Pelt-KleinJan E, Douwenga S, Smid EJ, Teusink B, van Mastrigt O. Lifestyle, metabolism and environmental adaptation in Lactococcus lactis. FEMS Microbiol Rev 2021; 44:804-820. [PMID: 32990728 DOI: 10.1093/femsre/fuaa033] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2020] [Accepted: 09/28/2020] [Indexed: 12/14/2022] Open
Abstract
Lactococcus lactis serves as a paradigm organism for the lactic acid bacteria (LAB). Extensive research into the molecular biology, metabolism and physiology of several model strains of this species has been fundamental for our understanding of the LAB. Genomic studies have provided new insights into the species L. lactis, including the resolution of the genetic basis of its subspecies division, as well as the control mechanisms involved in the fine-tuning of growth rate and energy metabolism. In addition, it has enabled novel approaches to study lactococcal lifestyle adaptations to the dairy application environment, including its adjustment to near-zero growth rates that are particularly relevant in the context of cheese ripening. This review highlights various insights in these areas and exemplifies the strength of combining experimental evolution with functional genomics and bacterial physiology research to expand our fundamental understanding of the L. lactis lifestyle under different environmental conditions.
Collapse
Affiliation(s)
- Michiel Kleerebezem
- Host-Microbe Interactomics Group, Animal Sciences Department, Wageningen University, De Elst 1, 6708 WD Wageningen, the Netherlands
| | - Herwig Bachmann
- Systems Bioinformatics, Vrije Universiteit Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, the Netherlands.,NIZO food research, Kernhemseweg 2, 6718 ZB Ede, the Netherlands
| | - Eunice van Pelt-KleinJan
- Systems Bioinformatics, Vrije Universiteit Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, the Netherlands.,TiFN Food & Nutrition, Nieuwe Kanaal 9A, 6709 PA Wageningen, the Netherlands
| | - Sieze Douwenga
- Systems Bioinformatics, Vrije Universiteit Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, the Netherlands.,TiFN Food & Nutrition, Nieuwe Kanaal 9A, 6709 PA Wageningen, the Netherlands
| | - Eddy J Smid
- Laboratory of Food Microbiology, Wageningen University, Bornse Weilanden 9, 6708 WG Wageningen, the Netherlands
| | - Bas Teusink
- Systems Bioinformatics, Vrije Universiteit Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, the Netherlands
| | - Oscar van Mastrigt
- Laboratory of Food Microbiology, Wageningen University, Bornse Weilanden 9, 6708 WG Wageningen, the Netherlands
| |
Collapse
|
5
|
Abstract
The impacts of linkers on dynamics, expression, and activity of biomacromolecules are often overlooked. This may be due, in part, to the lack of facile methods for incorporation and analysis of linkers that vary iteratively in both length and sequence composition. The protaTETHER method addresses this gap by enabling the incorporation of focused linker libraries at potentially any region in a protein sequence. In this chapter, we describe the generation and incorporation of linkers in a PKAc-GFP fusion protein and provide methods for the application and evaluation of the protaTETHER process.
Collapse
|
6
|
de Boer M, Cordes T, Poolman B. Kinetic Modelling of Transport Inhibition by Substrates in ABC Importers. J Mol Biol 2020; 432:5565-5576. [PMID: 32800784 DOI: 10.1016/j.jmb.2020.08.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 08/05/2020] [Accepted: 08/09/2020] [Indexed: 12/11/2022]
Abstract
Prokaryotic ATP-binding cassette (ABC) importers require a substrate-binding protein (SBP) for the capture and delivery of the cognate substrate to the transmembrane domain (TMD) of the transporter. Various biochemical compounds have been identified that bind to the SBP but are not transported. The mechanistic basis for the "non-cognate" substrates not being transported differs. Some non-cognate substrates fail to trigger the appropriate conformational change in the SBP, resulting in loss of affinity for the TMD or the inability to allosterically activate transport. In another mechanism, the SBP cannot release the bound non-cognate substrate. Here, we used rate equations to derive the steady-state transport rate of cognate substrates of an ABC importer and investigated how non-cognate substrates influence this rate. We found that under limiting non-cognate substrate concentrations, the transport rate remains unaltered for each of the mechanisms. In contrast, at saturating substrate and SBP concentrations, the effect of the non-cognate substrate depends heavily on the respective mechanism. For instance, the transport rate becomes zero when the non-cognate substrate cannot be released by the SBP. Yet it remains unaffected when substrate release is possible but the SBP cannot dock onto the TMDs. Our work shows how the different mechanisms of substrate inhibition impact the transport kinetics, which is relevant for understanding and manipulating solute fluxes and hence the propagation of cells in nutritionally complex milieus.
Collapse
Affiliation(s)
- Marijn de Boer
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Groningen, the Netherlands; Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, the Netherlands.
| | - Thorben Cordes
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Groningen, the Netherlands; Physical and Synthetic Biology, Faculty of Biology, Ludwig-Maximilians-Universität München, Großhadernerstr, 2-4, 82152 Planegg-Martinsried, Germany
| | - Bert Poolman
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, the Netherlands.
| |
Collapse
|
7
|
Willson BJ, Chapman LNM, Thomas GH. Evolutionary dynamics of membrane transporters and channels: enhancing function through fusion. Curr Opin Genet Dev 2019; 58-59:76-86. [DOI: 10.1016/j.gde.2019.07.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 07/19/2019] [Accepted: 07/23/2019] [Indexed: 02/05/2023]
|
8
|
de Boer M, Gouridis G, Muthahari YA, Cordes T. Single-Molecule Observation of Ligand Binding and Conformational Changes in FeuA. Biophys J 2019; 117:1642-1654. [PMID: 31537314 PMCID: PMC6838762 DOI: 10.1016/j.bpj.2019.08.005] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Revised: 07/15/2019] [Accepted: 08/02/2019] [Indexed: 12/01/2022] Open
Abstract
The specific binding of ligands by proteins and the coupling of this process to conformational changes is fundamental to protein function. We designed a fluorescence-based single-molecule assay and data analysis procedure that allows the simultaneous real-time observation of ligand binding and conformational changes in FeuA. The substrate-binding protein FeuA binds the ligand ferri-bacillibactin and delivers it to the ATP-binding cassette importer FeuBC, which is involved in bacterial iron uptake. The conformational dynamics of FeuA was assessed via Förster resonance energy transfer, whereas the presence of the ligand was probed by fluorophore quenching. We reveal that ligand binding shifts the conformational equilibrium of FeuA from an open to a closed conformation. Ligand binding occurs via an induced-fit mechanism, i.e., the ligand binds to the open state and subsequently triggers a rapid closing of the protein. However, FeuA also rarely samples the closed conformation without the involvement of the ligand. This shows that ligand interactions are not required for conformational changes in FeuA. However, ligand interactions accelerate the conformational change 10,000-fold and temporally stabilize the formed conformation 250-fold.
Collapse
Affiliation(s)
- Marijn de Boer
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Groningen, the Netherlands
| | - Giorgos Gouridis
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Groningen, the Netherlands; Physical and Synthetic Biology, Faculty of Biology, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany; KU Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, Leuven, Belgium
| | - Yusran Abdillah Muthahari
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Groningen, the Netherlands
| | - Thorben Cordes
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Groningen, the Netherlands; Physical and Synthetic Biology, Faculty of Biology, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany.
| |
Collapse
|
9
|
de Boer M, Gouridis G, Vietrov R, Begg SL, Schuurman-Wolters GK, Husada F, Eleftheriadis N, Poolman B, McDevitt CA, Cordes T. Conformational and dynamic plasticity in substrate-binding proteins underlies selective transport in ABC importers. eLife 2019; 8:44652. [PMID: 30900991 PMCID: PMC6450668 DOI: 10.7554/elife.44652] [Citation(s) in RCA: 72] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 03/22/2019] [Indexed: 12/20/2022] Open
Abstract
Substrate-binding proteins (SBPs) are associated with ATP-binding cassette importers and switch from an open to a closed conformation upon substrate binding, providing specificity for transport. We investigated the effect of substrates on the conformational dynamics of six SBPs and the impact on transport. Using single-molecule FRET, we reveal an unrecognized diversity of plasticity in SBPs. We show that a unique closed SBP conformation does not exist for transported substrates. Instead, SBPs sample a range of conformations that activate transport. Certain non-transported ligands leave the structure largely unaltered or trigger a conformation distinct from that of transported substrates. Intriguingly, in some cases, similar SBP conformations are formed by both transported and non-transported ligands. In this case, the inability for transport arises from slow opening of the SBP or the selectivity provided by the translocator. Our results reveal the complex interplay between ligand-SBP interactions, SBP conformational dynamics and substrate transport.
Collapse
Affiliation(s)
- Marijn de Boer
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Giorgos Gouridis
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands.,Physical and Synthetic Biology, Faculty of Biology, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany.,Laboratory of Molecular Bacteriology, Department of Microbiology and Immunology, Rega Institute for Medical Research, KU Leuven, Leuven, Belgium
| | - Ruslan Vietrov
- Department of Biochemistry, Groningen Biomolecular Science and Biotechnology Institute, University of Groningen, Groningen, The Netherlands.,Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Stephanie L Begg
- Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, Australia
| | - Gea K Schuurman-Wolters
- Department of Biochemistry, Groningen Biomolecular Science and Biotechnology Institute, University of Groningen, Groningen, The Netherlands.,Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Florence Husada
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Nikolaos Eleftheriadis
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Bert Poolman
- Department of Biochemistry, Groningen Biomolecular Science and Biotechnology Institute, University of Groningen, Groningen, The Netherlands.,Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Christopher A McDevitt
- Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, Australia.,Research Centre for Infectious Diseases, School of Biological Sciences, The University of Adelaide, Adelaide, Australia
| | - Thorben Cordes
- Molecular Microscopy Research Group, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands.,Physical and Synthetic Biology, Faculty of Biology, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
| |
Collapse
|
10
|
Licht A, Bommer M, Werther T, Neumann K, Hobe C, Schneider E. Structural and functional characterization of a maltose/maltodextrin ABC transporter comprising a single solute binding domain (MalE) fused to the transmembrane subunit MalF. Res Microbiol 2019; 170:1-12. [DOI: 10.1016/j.resmic.2018.08.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2018] [Revised: 08/15/2018] [Accepted: 08/28/2018] [Indexed: 01/21/2023]
|
11
|
OpuF, a New Bacillus Compatible Solute ABC Transporter with a Substrate-Binding Protein Fused to the Transmembrane Domain. Appl Environ Microbiol 2018; 84:AEM.01728-18. [PMID: 30097444 DOI: 10.1128/aem.01728-18] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2018] [Accepted: 08/08/2018] [Indexed: 01/20/2023] Open
Abstract
The accumulation of compatible solutes is a common defense of bacteria against the detrimental effects of high osmolarity. Uptake systems for these compounds are cornerstones in cellular osmostress responses because they allow the energy-preserving scavenging of osmostress protectants from environmental sources. Bacillus subtilis is well studied with respect to the import of compatible solutes and its five transport systems (OpuA, OpuB, OpuC, OpuD, and OpuE), for these stress protectants have previously been comprehensively studied. Building on this knowledge and taking advantage of the unabated appearance of new genome sequences of members of the genus Bacillus, we report here the discovery, physiological characterization, and phylogenomics of a new member of the Opu family of transporters, OpuF (OpuFA-OpuFB). OpuF is not present in B. subtilis but it is widely distributed in members of the large genus Bacillus OpuF is a representative of a subgroup of ATP-binding cassette (ABC) transporters in which the substrate-binding protein (SBP) is fused to the transmembrane domain (TMD). We studied the salient features of the OpuF transporters from Bacillus infantis and Bacillus panaciterrae by functional reconstitution in a B. subtilis chassis strain lacking known Opu transporters. A common property of the examined OpuF systems is their substrate profile; OpuF mediates the import of glycine betaine, proline betaine, homobetaine, and the marine osmolyte dimethylsulfoniopropionate (DMSP). An in silico model of the SBP domain of the TMD-SBP hybrid protein OpuFB was established. It revealed the presence of an aromatic cage, a structural feature commonly present in ligand-binding sites of compatible solute importers.IMPORTANCE The high-affinity import of compatible solutes from environmental sources is an important aspect of the cellular defense of many bacteria and archaea against the harmful effects of high external osmolarity. The accumulation of these osmostress protectants counteracts high-osmolarity-instigated water efflux, a drop in turgor to nonphysiological values, and an undue increase in molecular crowding of the cytoplasm; they thereby foster microbial growth under osmotically unfavorable conditions. Importers for compatible solutes allow the energy-preserving scavenging of osmoprotective and physiologically compliant organic solutes from environmental sources. We report here the discovery, exemplary physiological characterization, and phylogenomics of a new compatible solute importer, OpuF, widely found in members of the Bacillus genus. The OpuF system is a representative of a growing subgroup of ABC transporters in which the substrate-scavenging function of the substrate-binding protein (SBP) and the membrane-embedded substrate translocating subunit (TMD) are fused into a single polypeptide chain.
Collapse
|