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Tempelhagen L, Ayer A, Culham DE, Stocker R, Wood JM. Cultivation at high osmotic pressure confers ubiquinone 8–independent protection of respiration on Escherichia coli. J Biol Chem 2020. [DOI: 10.1016/s0021-9258(17)49909-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Tempelhagen L, Ayer A, Culham DE, Stocker R, Wood JM. Cultivation at high osmotic pressure confers ubiquinone 8-independent protection of respiration on Escherichia coli. J Biol Chem 2019; 295:981-993. [PMID: 31826918 DOI: 10.1074/jbc.ra119.011549] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Revised: 12/11/2019] [Indexed: 11/06/2022] Open
Abstract
Ubiquinone 8 (coenzyme Q8 or Q8) mediates electron transfer within the aerobic respiratory chain, mitigates oxidative stress, and contributes to gene expression in Escherichia coli In addition, Q8 was proposed to confer bacterial osmotolerance by accumulating during growth at high osmotic pressure and altering membrane stability. The osmolyte trehalose and membrane lipid cardiolipin accumulate in E. coli cells cultivated at high osmotic pressure. Here, Q8 deficiency impaired E. coli growth at low osmotic pressure and rendered growth osmotically sensitive. The Q8 deficiency impeded cellular O2 uptake and also inhibited the activities of two proton symporters, the osmosensing transporter ProP and the lactose transporter LacY. Q8 supplementation decreased membrane fluidity in liposomes, but did not affect ProP activity in proteoliposomes, which is respiration-independent. Liposomes and proteoliposomes prepared with E. coli lipids were used for these experiments. Similar oxygen uptake rates were observed for bacteria cultivated at low and high osmotic pressures. In contrast, respiration was dramatically inhibited when bacteria grown at the same low osmotic pressure were shifted to high osmotic pressure. Thus, respiration was restored during prolonged growth of E. coli at high osmotic pressure. Of note, bacteria cultivated at low and high osmotic pressures had similar Q8 concentrations. The protection of respiration was neither diminished by cardiolipin deficiency nor conferred by trehalose overproduction during growth at low osmotic pressure, but rather might be achieved by Q8-independent respiratory chain remodeling. We conclude that osmotolerance is conferred through Q8-independent protection of respiration, not by altering physical properties of the membrane.
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Affiliation(s)
- Laura Tempelhagen
- Department of Molecular and Cellular Biology, University of Guelph, 488 Gordon Street, Guelph, Ontario N1G 2W1, Canada
| | - Anita Ayer
- Vascular Biology Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales 2010, Australia.,St. Vincent's Clinical School, University of New South Wales Medicine, Kensington, New South Wales 2050, Australia
| | - Doreen E Culham
- Department of Molecular and Cellular Biology, University of Guelph, 488 Gordon Street, Guelph, Ontario N1G 2W1, Canada
| | - Roland Stocker
- Vascular Biology Division, Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales 2010, Australia.,St. Vincent's Clinical School, University of New South Wales Medicine, Kensington, New South Wales 2050, Australia
| | - Janet M Wood
- Department of Molecular and Cellular Biology, University of Guelph, 488 Gordon Street, Guelph, Ontario N1G 2W1, Canada
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Culham DE, Shkel IA, Record MT, Wood JM. Contributions of Coulombic and Hofmeister Effects to the Osmotic Activation of Escherichia coli Transporter ProP. Biochemistry 2016; 55:1301-13. [PMID: 26871755 DOI: 10.1021/acs.biochem.5b01169] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Osmosensing transporters mediate osmolyte accumulation to forestall cellular dehydration as the extracellular osmolality increases. ProP is a bacterial osmolyte-H(+) symporter, a major facilitator superfamily member, and a paradigm for osmosensing. ProP activity is a sigmoid function of the osmolality. It is determined by the osmolality, not the magnitude or direction of the osmotic shift, in cells and salt-loaded proteoliposomes. The activation threshold varies directly with the proportion of anionic phospholipid in cells and proteoliposomes. The osmosensory mechanism was probed by varying the salt composition and concentration outside and inside proteoliposomes. Data analysis was based on the hypothesis that the fraction of maximal transporter activity at a particular luminal salt concentration reflects the proportion of ProP molecules in an active conformation. ProP attained the same activity at the same osmolality when diverse, membrane-impermeant salts were added to the external medium. Contributions of Coulombic and/or Hofmeister salt effects to ProP activation were examined by varying the luminal salt cation (K(+) and Na(+)) and anion (chloride, phosphate, and sulfate) composition and then systematically increasing the luminal salt concentration by increasing the external osmolality. ProP activity increased with the sixth power of the univalent cation concentration, independent of the type of anion. This indicates that salt activation of ProP is a Coulombic, cation effect resulting from salt cation accumulation and not site-specific cation binding. Possible origins of this Coulombic effect include folding or assembly of anionic cytoplasmic ProP domains, an increase in local membrane surface charge density, and/or the juxtaposition of anionic protein and membrane surfaces during activation.
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Affiliation(s)
- Doreen E Culham
- Department of Molecular and Cellular Biology, University of Guelph , Guelph, ON N1G 2W1, Canada
| | - Irina A Shkel
- Departments of Biochemistry and Chemistry, University of Wisconsin , Madison, Wisconsin 53706, United States
| | - M Thomas Record
- Departments of Biochemistry and Chemistry, University of Wisconsin , Madison, Wisconsin 53706, United States
| | - Janet M Wood
- Department of Molecular and Cellular Biology, University of Guelph , Guelph, ON N1G 2W1, Canada
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Abstract
Escherichia coli and Salmonella encounter osmotic pressure variations in natural environments that include host tissues, food, soil, and water. Osmotic stress causes water to flow into or out of cells, changing their structure, physics, and chemistry in ways that perturb cell functions. E. coli and Salmonella limit osmotically induced water fluxes by accumulating and releasing electrolytes and small organic solutes, some denoted compatible solutes because they accumulate to high levels without disturbing cell functions. Osmotic upshifts inhibit membrane-based energy transduction and macromolecule synthesis while activating existing osmoregulatory systems and specifically inducing osmoregulatory genes. The osmoregulatory response depends on the availability of osmoprotectants (exogenous organic compounds that can be taken up to become compatible solutes). Without osmoprotectants, K+ accumulates with counterion glutamate, and compatible solute trehalose is synthesized. Available osmoprotectants are taken up via transporters ProP, ProU, BetT, and BetU. The resulting compatible solute accumulation attenuates the K+ glutamate response and more effectively restores cell hydration and growth. Osmotic downshifts abruptly increase turgor pressure and strain the cytoplasmic membrane. Mechanosensitive channels like MscS and MscL open to allow nonspecific solute efflux and forestall cell lysis. Research frontiers include (i) the osmoadaptive remodeling of cell structure, (ii) the mechanisms by which osmotic stress alters gene expression, (iii) the mechanisms by which transporters and channels detect and respond to osmotic pressure changes, (iv) the coordination of osmoregulatory programs and selection of available osmoprotectants, and (v) the roles played by osmoregulatory mechanisms as E. coli and Salmonella survive or thrive in their natural environments.
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Falcioni F, Bühler B, Schmid A. Efficient hydroxyproline production from glucose in minimal media byCorynebacterium glutamicum. Biotechnol Bioeng 2014; 112:322-30. [DOI: 10.1002/bit.25442] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Revised: 08/06/2014] [Accepted: 08/18/2014] [Indexed: 11/09/2022]
Affiliation(s)
- Francesco Falcioni
- Department of Biochemical and Chemical Engineering; Laboratory of Chemical Biotechnology; TU Dortmund University; Emil-Figge-Strasse 66 Dortmund 44227 Germany
| | - Bruno Bühler
- Department of Biochemical and Chemical Engineering; Laboratory of Chemical Biotechnology; TU Dortmund University; Emil-Figge-Strasse 66 Dortmund 44227 Germany
| | - Andreas Schmid
- Department of Biochemical and Chemical Engineering; Laboratory of Chemical Biotechnology; TU Dortmund University; Emil-Figge-Strasse 66 Dortmund 44227 Germany
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Distinct effects of sorbic acid and acetic acid on the electrophysiology and metabolism of Bacillus subtilis. Appl Environ Microbiol 2014; 80:5918-26. [PMID: 25038097 DOI: 10.1128/aem.01391-14] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Sorbic acid and acetic acid are among the weak organic acid preservatives most commonly used to improve the microbiological stability of foods. They have similar pKa values, but sorbic acid is a far more potent preservative. Weak organic acids are most effective at low pH. Under these circumstances, they are assumed to diffuse across the membrane as neutral undissociated acids. We show here that the level of initial intracellular acidification depends on the concentration of undissociated acid and less on the nature of the acid. Recovery of the internal pH depends on the presence of an energy source, but acidification of the cytosol causes a decrease in glucose flux. Furthermore, sorbic acid is a more potent uncoupler of the membrane potential than acetic acid. Together these effects may also slow the rate of ATP synthesis significantly and may thus (partially) explain sorbic acid's effectiveness.
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Karasawa A, Swier LJYM, Stuart MCA, Brouwers J, Helms B, Poolman B. Physicochemical factors controlling the activity and energy coupling of an ionic strength-gated ATP-binding cassette (ABC) transporter. J Biol Chem 2013; 288:29862-71. [PMID: 23979139 DOI: 10.1074/jbc.m113.499327] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Cells control their volume through the accumulation of compatible solutes. The bacterial ATP-binding cassette transporter OpuA couples compatible solute uptake to ATP hydrolysis. Here, we study the gating mechanism and energy coupling of OpuA reconstituted in lipid nanodiscs. We show that anionic lipids are essential both for the gating and the energy coupling. The tight coupling between substrate binding on extracellular domains and ATP hydrolysis by cytoplasmic nucleotide-binding domains allows the study of transmembrane signaling in nanodiscs. From the tight coupling between processes at opposite sides of the membrane, we infer that the ATPase activity of OpuA in nanodiscs reflects solute translocation. Intriguingly, the substrate-dependent, ionic strength-gated ATPase activity of OpuA in nanodiscs is at least an order of magnitude higher than in lipid vesicles (i.e. with identical membrane lipid composition, ionic strength, and nucleotide and substrate concentrations). Even with the chemical components the same, the lateral pressure (profile) of the nanodiscs will differ from that of the vesicles. We thus propose that membrane tension limits translocation in vesicular systems. Increased macromolecular crowding does not activate OpuA but acts synergistically with ionic strength, presumably by favoring gating interactions of like-charged surfaces via excluded volume effects.
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Affiliation(s)
- Akira Karasawa
- From the Departments of Biochemistry and Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, Netherlands Proteomics Centre
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Culham DE, Meinecke M, Wood JM. Impacts of the osmolality and the lumenal ionic strength on osmosensory transporter ProP in proteoliposomes. J Biol Chem 2012; 287:27813-22. [PMID: 22740696 DOI: 10.1074/jbc.m112.387936] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
H(+) symporter ProP serves as a paradigm for the study of osmosensing. ProP attains the same activity at the same osmolality when the medium outside cells or proteoliposomes is supplemented with diverse, membrane-impermeant solutes. The osmosensory mechanism of ProP has been probed by varying the solvent within membrane vesicles and proteoliposomes. ProP activation was not ion specific, did not require K(+), and could be elicited by large, uncharged solutes polyethylene glycols (PEGS). We hypothesized that ProP is an ionic strength sensor and lumenal macromolecules activate ProP by altering ion activities. The attainable range of lumenal ionic strength was expanded by lowering the phosphate concentration within proteoliposomes. ProP activity at high osmolality, but not the osmolality, yielding half-maximal activity (Π(1/2)/RT), decreased with the lumenal phosphate concentration. This was attributed to acidification of the proteoliposome lumen due to H(+)-proline symport. The ionic strength yielding half-maximal ProP activity was more anion-dependent than Π(1/2)/RT for proteoliposomes loaded with citrate, sulfate, phosphate, chloride, or iodide. The anion effects followed the Hofmeister series. Lumenal bovine serum albumin (BSA) lowered the lumenal ionic strength at which ProP became active. Osmolality measurements documented the non-idealities of solutions including potassium phosphate and other solutes. The impacts of PEGS and BSA on ion activities did not account for their impacts on ProP activity. The effects of the tested solutes on ProP appear to be non-coulombic in nature. They may arise from effects of preferential interactions and macromolecular crowding on the membrane or on ProP.
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Affiliation(s)
- Doreen E Culham
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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Abstract
To thrive, cells must control their own physical and chemical properties. This process is known as cellular homeostasis. The dilute solutions traditionally favored by experimenters do not simulate the cytoplasm, where macromolecular crowding and preferential interactions among constituents may dominate critical processes. Solutions that do simulate cytoplasmic conditions are now being characterized. Corresponding cytoplasmic properties can be varied systematically by imposing osmotic stress. This osmotic stress approach is revealing how cytoplasmic properties modulate protein folding and protein?nucleic acid interactions. Results suggest that cytoplasmic homeostasis may require adjustments to multiple, interwoven cytoplasmic properties. Osmosensory transporters with diverse structures and bioenergetic mechanisms activate in response to osmotic stress as other proteins inactivate. These transporters are serving as paradigms for the study of in vivo protein-solvent interactions. Experimenters have proposed three different osmosensory mechanisms. Distinct mechanisms may exist, or these proposals may reflect different perceptions of a single, unifying mechanism.
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Affiliation(s)
- Janet M Wood
- Department of Molecular and Cellular Biology, University of Guelph, Ontario, N1G 2W1, Canada.
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Karasawa A, Erkens GB, Berntsson RPA, Otten R, Schuurman-Wolters GK, Mulder FAA, Poolman B. Cystathionine β-synthase (CBS) domains 1 and 2 fulfill different roles in ionic strength sensing of the ATP-binding cassette (ABC) transporter OpuA. J Biol Chem 2011; 286:37280-91. [PMID: 21878634 PMCID: PMC3199475 DOI: 10.1074/jbc.m111.284059] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2011] [Revised: 08/26/2011] [Indexed: 01/05/2023] Open
Abstract
The cystathionine β-synthase module of OpuA in conjunction with an anionic membrane surface acts as a sensor of internal ionic strength, which allows the protein to respond to osmotic stress. We now show by chemical modification and cross-linking studies that CBS2-CBS2 interface residues are critical for transport activity and/or ionic regulation of transport, whereas CBS1 serves no functional role. We establish that Cys residues in CBS1, CBS2, and the nucleotide-binding domain are more accessible for cross-linking at high than low ionic strength, indicating that these domains undergo conformational changes when transiting between the active and inactive state. Structural analyses suggest that the cystathionine β-synthase module is largely unstructured. Moreover, we could substitute CBS1 by a linker and preserve ionic regulation of transport. These data suggest that CBS1 serves as a linker and the structured CBS2-CBS2 interface forms a hinge point for ionic strength-dependent rearrangements that are transmitted to the nucleotide-binding domain and thereby affect translocation activity.
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Affiliation(s)
- Akira Karasawa
- From the Departments of Biochemistry and Biophysical Chemistry, Groningen Biomolecular Science and Biotechnology Institute, Netherlands Proteomics Centre and Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Guus B. Erkens
- From the Departments of Biochemistry and Biophysical Chemistry, Groningen Biomolecular Science and Biotechnology Institute, Netherlands Proteomics Centre and Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Ronnie P.-A. Berntsson
- From the Departments of Biochemistry and Biophysical Chemistry, Groningen Biomolecular Science and Biotechnology Institute, Netherlands Proteomics Centre and Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Renee Otten
- From the Departments of Biochemistry and Biophysical Chemistry, Groningen Biomolecular Science and Biotechnology Institute, Netherlands Proteomics Centre and Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Gea K. Schuurman-Wolters
- From the Departments of Biochemistry and Biophysical Chemistry, Groningen Biomolecular Science and Biotechnology Institute, Netherlands Proteomics Centre and Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Frans A. A. Mulder
- From the Departments of Biochemistry and Biophysical Chemistry, Groningen Biomolecular Science and Biotechnology Institute, Netherlands Proteomics Centre and Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
| | - Bert Poolman
- From the Departments of Biochemistry and Biophysical Chemistry, Groningen Biomolecular Science and Biotechnology Institute, Netherlands Proteomics Centre and Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
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Ziegler C, Bremer E, Krämer R. The BCCT family of carriers: from physiology to crystal structure. Mol Microbiol 2011; 78:13-34. [PMID: 20923416 DOI: 10.1111/j.1365-2958.2010.07332.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Increases in the environmental osmolarity are key determinants for the growth of microorganisms. To ensure a physiologically acceptable level of cellular hydration and turgor at high osmolarity, many bacteria accumulate compatible solutes. Osmotically controlled uptake systems allow the scavenging of these compounds from scarce environmental sources as effective osmoprotectants. A number of these systems belong to the BCCT family (betaine-choline-carnitine-transporter), sodium- or proton-coupled transporters (e.g. BetP and BetT respectively) that are ubiquitous in microorganisms. The BCCT family also contains CaiT, an L-carnitine/γ-butyrobetaine antiporter that is not involved in osmotic stress responses. The glycine betaine transporter BetP from Corynebacterium glutamicum is a representative for osmoregulated symporters of the BCCT family and functions both as an osmosensor and osmoregulator. The crystal structure of BetP in an occluded conformation in complex with its substrate glycine betaine and two crystal structures of CaiT in an inward-facing open conformation in complex with L-carnitine and γ-butyrobetaine were reported recently. These structures and the wealth of biochemical data on the activity control of BetP in response to osmotic stress enable a correlation between the sensing of osmotic stress by a transporter protein with the ensuing regulation of transport activity. Molecular determinants governing the high-affinity binding of the compatible solutes by BetP and CaiT, the coupling in symporters and antiporters, and the osmoregulatory properties are discussed in detail for BetP and various BCCT carriers.
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Affiliation(s)
- Christine Ziegler
- Max-Planck Institute for Biophysics, Max-von-Laue Street 3, D-60438 Frankfurt, Germany
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Keates RAB, Culham DE, Vernikovska YI, Zuiani AJ, Boggs JM, Wood JM. Transmembrane helix I and periplasmic loop 1 of Escherichia coli ProP are involved in osmosensing and osmoprotectant transport. Biochemistry 2010; 49:8847-56. [PMID: 20828170 DOI: 10.1021/bi101281f] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Osmoregulatory transporters stimulate bacterial growth by mediating osmoprotectant uptake in response to increasing osmotic pressure. The ProP protein of Escherichia coli transports proline and other osmoprotectants. Like LacY, ProP is a member of the major facilitator superfamily and a H(+)-solute symporter. ProP is regulated by osmotic pressure via a membrane potential-dependent mechanism. A homology model predicts that ionizable and polar residues, highly conserved among ProP homologues, cluster deep within the N-terminal helix bundle of ProP. Chemical labeling of introduced cysteine (Cys) residues supported the homology model by confirming the predicted positions of transmembrane helix I (TMI) and periplasmic loop 1. Replacements of residues in the putative polar cluster impaired or altered ProP function, suggesting that they are important for osmosensing and may interact with the transport substrates. Asn34, Glu37, Phe41, Tyr44, and Ala48 line the most polar face of TMI; Tyr44 is on the periplasmic side of the putative polar cluster, and Ala59 is in periplasmic loop 1. The N-ethylmaleimide reactivities of Cys introduced at positions 41, 44, 48, and 59 increased with osmotic pressure, whereas the reactivities of those at cytoplasm-proximal positions 34 and 37 did not. Replacements of polar cluster residues that blocked transport also affected the NEM reactivity of Cys44 and its osmolality dependence. This report and previous work suggest that conformational changes associated with osmosensing may shift the equilibria between outward- and inward-facing transport pathway intermediates.
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Affiliation(s)
- Robert A B Keates
- Department of Molecular and Cellular Biology, University of Guelph, 488 Gordon Street, Guelph, Ontario, Canada
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Wolters JC, Berntsson RPA, Gul N, Karasawa A, Thunnissen AMWH, Slotboom DJ, Poolman B. Ligand binding and crystal structures of the substrate-binding domain of the ABC transporter OpuA. PLoS One 2010; 5:e10361. [PMID: 20454456 PMCID: PMC2861598 DOI: 10.1371/journal.pone.0010361] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2010] [Accepted: 03/31/2010] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The ABC transporter OpuA from Lactococcus lactis transports glycine betaine upon activation by threshold values of ionic strength. In this study, the ligand binding characteristics of purified OpuA in a detergent-solubilized state and of its substrate-binding domain produced as soluble protein (OpuAC) was characterized. PRINCIPAL FINDINGS The binding of glycine betaine to purified OpuA and OpuAC (K(D) = 4-6 microM) did not show any salt dependence or cooperative effects, in contrast to the transport activity. OpuAC is highly specific for glycine betaine and the related proline betaine. Other compatible solutes like proline and carnitine bound with affinities that were 3 to 4 orders of magnitude lower. The low affinity substrates were not noticeably transported by membrane-reconstituted OpuA. OpuAC was crystallized in an open (1.9 A) and closed-liganded (2.3 A) conformation. The binding pocket is formed by three tryptophans (Trp-prism) coordinating the quaternary ammonium group of glycine betaine in the closed-liganded structure. Even though the binding site of OpuAC is identical to that of its B. subtilis homolog, the affinity for glycine betaine is 4-fold higher. CONCLUSIONS Ionic strength did not affect substrate binding to OpuA, indicating that regulation of transport is not at the level of substrate binding, but rather at the level of translocation. The overlap between the crystal structures of OpuAC from L.lactis and B.subtilis, comprising the classical Trp-prism, show that the differences observed in the binding affinities originate from outside of the ligand binding site.
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Affiliation(s)
- Justina C. Wolters
- Biochemistry Department, Groningen Biomolecular Sciences and Biotechnology Institute, Netherlands Proteomics Centre, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Ronnie P-A. Berntsson
- Biochemistry Department, Groningen Biomolecular Sciences and Biotechnology Institute, Netherlands Proteomics Centre, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Nadia Gul
- Biochemistry Department, Groningen Biomolecular Sciences and Biotechnology Institute, Netherlands Proteomics Centre, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Akira Karasawa
- Biochemistry Department, Groningen Biomolecular Sciences and Biotechnology Institute, Netherlands Proteomics Centre, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Andy-Mark W. H. Thunnissen
- Biophysical Chemistry Department, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
| | - Dirk-Jan Slotboom
- Biochemistry Department, Groningen Biomolecular Sciences and Biotechnology Institute, Netherlands Proteomics Centre, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Bert Poolman
- Biochemistry Department, Groningen Biomolecular Sciences and Biotechnology Institute, Netherlands Proteomics Centre, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
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Identification of Bacillus cereus genes specifically expressed during growth at low temperatures. Appl Environ Microbiol 2010; 76:2562-73. [PMID: 20190083 DOI: 10.1128/aem.02348-09] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
The mechanisms involved in the ability of Bacillus cereus to multiply at low temperatures were investigated. It was assumed that many genes involved in cold acclimation would be upregulated at low temperatures. Recombinase-based in vivo expression technology (IVET) was adapted to the detection of the transient activation of B. cereus promoters during growth at 10 degrees C. Four independent screenings of a promoter library from type strain ATCC 14579 were performed, and 17 clones were isolated. They corresponded to 17 promoter regions that displayed reproducibly elevated expression at 10 degrees C relative to expression at 30 degrees C. This analysis revealed several genes that may be important for B. cereus to grow successfully under the restrictive conditions of cold habitats. Among them, a locus corresponding to open reading frames BC5402 to BC5398, harboring a lipase-encoding gene and a putative transcriptional regulator, was identified three times. While a mutation in the putative regulator-encoding gene did not cause any particular phenotype, a mutant deficient in the lipase-encoding gene showed reduced growth abilities at low temperatures compared with the parental strain. The mutant did not change its fatty acid profiles in the same way as the wild type when grown at 12 degrees C instead of 37 degrees C. This study demonstrates the feasibility of a promoter trap strategy for identifying cold-induced genes. It outlines a first picture of the different processes involved in B. cereus cold acclimation.
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Protein localization in Escherichia coli cells: comparison of the cytoplasmic membrane proteins ProP, LacY, ProW, AqpZ, MscS, and MscL. J Bacteriol 2009; 192:912-24. [PMID: 20008071 DOI: 10.1128/jb.00967-09] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Fluorescence microscopy has revealed that the phospholipid cardiolipin (CL) and FlAsH-labeled transporters ProP and LacY are concentrated at the poles of Escherichia coli cells. The proportion of CL among E. coli phospholipids can be varied in vivo as it is decreased by cls mutations and it increases with the osmolality of the growth medium. In this report we compare the localization of CL, ProP, and LacY with that of other cytoplasmic membrane proteins. The proportion of cells in which FlAsH-labeled membrane proteins were concentrated at the cell poles was determined as a function of protein expression level and CL content. Each tagged protein was expressed from a pBAD24-derived plasmid; tagged ProP was also expressed from the chromosome. The osmosensory transporter ProP and the mechanosensitive channel MscS concentrated at the poles at frequencies correlated with the cellular CL content. The lactose transporter LacY was found at the poles at a high and CL-independent frequency. ProW (a component of the osmoregulatory transporter ProU), AqpZ (an aquaporin), and MscL (a mechanosensitive channel) were concentrated at the poles in a minority of cells, and this polar localization was CL independent. The frequency of polar localization was independent of induction (at arabinose concentrations up to 1 mM) for proteins encoded by pBAD24-derived plasmids. Complementation studies showed that ProW, AqpZ, MscS, and MscL remained functional after introduction of the FlAsH tag (CCPGCC). These data suggest that CL-dependent polar localization in E. coli cells is not a general characteristic of transporters, channels, or osmoregulatory proteins. Polar localization can be frequent and CL independent (as observed for LacY), frequent and CL dependent (as observed for ProP and MscS), or infrequent (as observed for AqpZ, ProW, and MscL).
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Romantsov T, Guan Z, Wood JM. Cardiolipin and the osmotic stress responses of bacteria. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:2092-100. [PMID: 19539601 DOI: 10.1016/j.bbamem.2009.06.010] [Citation(s) in RCA: 161] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2008] [Revised: 06/07/2009] [Accepted: 06/10/2009] [Indexed: 11/29/2022]
Abstract
Cells control their own hydration by accumulating solutes when they are exposed to high osmolality media and releasing solutes in response to osmotic down-shocks. Osmosensory transporters mediate solute accumulation and mechanosensitive channels mediate solute release. Escherichia coli serves as a paradigm for studies of cellular osmoregulation. Growth in media of high salinity alters the phospholipid headgroup and fatty acid compositions of bacterial cytoplasmic membranes, in many cases increasing the ratio of anionic to zwitterionic lipid. In E. coli, the proportion of cardiolipin (CL) increases as the proportion of phosphatidylethanolamine (PE) decreases when osmotic stress is imposed with an electrolyte or a non-electrolyte. Osmotic induction of the gene encoding CL synthase (cls) contributes to these changes. The proportion of phosphatidylglycerol (PG) increases at the expense of PE in cls(-) bacteria and, in Bacillus subtilis, the genes encoding CL and PG synthases (clsA and pgsA) are both osmotically regulated. CL is concentrated at the poles of diverse bacterial cells. A FlAsH-tagged variant of osmosensory transporter ProP is also concentrated at E. coli cell poles. Polar concentration of ProP is CL-dependent whereas polar concentration of its paralogue LacY, a H(+)-lactose symporter, is not. The proportion of anionic lipids (CL and PG) modulates the function of ProP in vivo and in vitro. These effects suggest that the osmotic induction of CL synthesis and co-localization of ProP with CL at the cell poles adjust the osmolality range over which ProP activity is controlled by placing it in a CL-rich membrane environment. In contrast, a GFP-tagged variant of mechanosensitive channel MscL is not concentrated at the cell poles but anionic lipids bind to a specific site on each subunit of MscL and influence its function in vitro. The sub-cellular locations and lipid dependencies of other osmosensory systems are not known. Varying CL content is a key element of osmotic adaptation by bacteria but much remains to be learned about its roles in the localization and function of osmoregulatory proteins.
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Affiliation(s)
- Tatyana Romantsov
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada N1G 2W1
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Sayeed WMH, Baenziger JE. Structural characterization of the osmosensor ProP. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:1108-15. [PMID: 19366597 DOI: 10.1016/j.bbamem.2009.01.010] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2008] [Revised: 01/09/2009] [Accepted: 01/21/2009] [Indexed: 11/20/2022]
Abstract
ProP, an osmoprotectant symporter from the major facilitator superfamily was expressed, purified and reconstituted into proteoliposomes that are amenable to structural characterization using infrared spectroscopy. Infrared spectra recorded in both (1)H(2)O and (2)H(2)O buffers reveal amide I band shapes that are characteristic of a predominantly alpha-helical protein, and that are similar to those recorded from the well-characterized homolog, lactose permease (LacY). Curve-fit analysis shows that ProP and LacY both exhibit a high alpha-helical content. Both proteins undergo extensive peptide hydrogen-deuterium exchange after exposure to (2)H(2)O, but are surprisingly thermally stable with denaturation temperatures greater than 60 degrees C. 25-30% of the peptide hydrogens in both ProP and LacY are resistant to exchange after 72 h in (2)H(2)O at 4 degrees C. Surprisingly, these exchange resistant peptide hydrogens exchange completely for deuterium at temperatures below those that lead to denaturation. Our results show that ProP adopts a highly alpha-helical fold similar to that of LacY, and that both transmembrane folds exhibit unusually high temperature-sensitive solvent accessibility. The results provide direct evidence that ProP adopts a structure consistent with other major facilitator superfamily members.
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Affiliation(s)
- Wajid M H Sayeed
- Department of Biochemistry, University of Ottawa, 451 Smyth Rd., Ottawa, Ontario, Canada K1H 8M5
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Culham DE, Vernikovska Y, Tschowri N, Keates RAB, Wood JM, Boggs JM. Periplasmic loops of osmosensory transporter ProP in Escherichia coli are sensitive to osmolality. Biochemistry 2009; 47:13584-93. [PMID: 19049385 DOI: 10.1021/bi801576x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
ProP is an osmosensory transporter. The activities of ProP and ProP*, a cysteine-less, His(6)-tagged ProP variant, increase with osmotic pressure in cells and proteoliposomes. In proteoliposomes, ProP activity is osmolality-dependent only if the magnitude of the membrane potential (DeltaPsi) exceeds 100 mV. Some amino acid replacements rendered ProP activity osmolality-insensitive [e.g., Y44M in transmembrane segment 1 (TMI); S62C in periplasmic loop 1 (loop P1)], whereas others elevated the osmolality at which ProP activates (e.g., A59C). This suggested that the environments and/or conformations of TMI and loop P1 might be osmolality-dependent. This report correlates structural dynamics of ProP with osmoregulation of its transport activity. Residues in periplasmic loops were replaced with Cys, and changes in their environments were detected by monitoring their reactivities with N-ethylmaleimide (NEM). Increasing osmolality markedly increased the NEM reactivity of some Cys residues (e.g., C59, loop P1; C415-C418, loop P6) but not others (e.g., C293, loop P4; C348, loop P5). The NEM reactivity of C62 was insensitive to osmolality, as expected. Substitution Y44M rendered the transport activities of ProP*-A59C and ProP*-Q415C, and the NEM reactivities of the introduced Cys, osmolality-insensitive. Furthermore, osmolality did not affect the reactivity of C59 in cells lacking a protonmotive force, consistent with evidence that DeltaPsi is required for osmosensing by ProP. These results indicate that the osmotically induced increases in NEM reactivity of C59 and C415 in energized bacteria are due to a conformational change of ProP in response to osmolality. They therefore constitute the first direct evidence of an osmotically induced conformational change associated with osmosensing by a transporter.
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Affiliation(s)
- Doreen E Culham
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada N1G 2W1
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