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Elston R, Mulligan C, Thomas GH. Flipping the switch: dynamic modulation of membrane transporter activity in bacteria. MICROBIOLOGY (READING, ENGLAND) 2023; 169. [PMID: 37948297 DOI: 10.1099/mic.0.001412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2023]
Abstract
The controlled entry and expulsion of small molecules across the bacterial cytoplasmic membrane is essential for efficient cell growth and cellular homeostasis. While much is known about the transcriptional regulation of genes encoding transporters, less is understood about how transporter activity is modulated once the protein is functional in the membrane, a potentially more rapid and dynamic level of control. In this review, we bring together literature from the bacterial transport community exemplifying the extensive and diverse mechanisms that have evolved to rapidly modulate transporter function, predominantly by switching activity off. This includes small molecule feedback, inhibition by interaction with small peptides, regulation through binding larger signal transduction proteins and, finally, the emerging area of controlled proteolysis. Many of these examples have been discovered in the context of metal transport, which has to finely balance active accumulation of elements that are essential for growth but can also quickly become toxic if intracellular homeostasis is not tightly controlled. Consistent with this, these transporters appear to be regulated at multiple levels. Finally, we find common regulatory themes, most often through the fusion of additional regulatory domains to transporters, which suggest the potential for even more widespread regulation of transporter activity in biology.
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Affiliation(s)
- Rory Elston
- Department of Biology, University of York, York, UK
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2
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Ozturk TN, Coumoundouros C, Culham DE, Wood JM. Structural Determinants and Functional Significance of Dimerization for Osmosensing Transporter ProP in Escherichia coli. Biochemistry 2023; 62:118-133. [PMID: 36516499 DOI: 10.1021/acs.biochem.2c00393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Osmosensing transporter ProP forestalls cellular dehydration by detecting environments with high osmotic pressure and mediating the accumulation of organic osmolytes by bacterial cells. It is composed of 12 transmembrane helices with cytoplasmic N- and C-termini. In Escherichia coli, dimers form when the C-terminal domains of ProP molecules form homodimeric, antiparallel, α-helical coiled coils. No dominant negative effect was detected when inactive and active ProP molecules formed heterodimers in vivo. Purification of ProP in detergent dodecylmaltoside yielded monomers, which were functional after reconstitution in proteoliposomes. With other evidence, this suggests that ProP monomers function independently whether in the monomeric or dimeric state. Amino acid replacements that disrupted or reversed the coiled coil did not prevent in vivo dimerization of ProP detected with a bacterial two-hybrid system. Maleimide labeling detected no osmolality-dependent variation in the reactivities of cysteine residues introduced to transmembrane helix (TM) XII. In contrast, coarse-grained molecular dynamic simulations detected deformation of the lipid around TMs III and VI, on the lipid-exposed protein surface opposite to TM XII. This suggests that the dimer interface of ProP includes the surfaces of TMs III and VI, not of TM XII as previously suggested by crosslinking data. Homology modeling suggested that coiled-coil formation and dimerization via such an interface are not mutually exclusive. In previous work, alterations to the C-terminal coiled coil blocked co-localization of ProP with phospholipid cardiolipin at E. coli cell poles. Thus, dimerization may contribute to ProP targeting, adjust its lipid environment, and hence indirectly modify its osmotic stress response.
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Affiliation(s)
- Tugba N Ozturk
- Department of Biochemistry and Molecular Biophysics, Washington University in Saint Louis, Saint Louis, Missouri63110, United States.,Theoretical Molecular Biophysics Laboratory, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland20814, United States
| | - Chelsea Coumoundouros
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, CanadaN1G 2 W1
| | - Doreen E Culham
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, CanadaN1G 2 W1
| | - Janet M Wood
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, CanadaN1G 2 W1
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3
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Wilcox XE, Chung CB, Slade KM. Macromolecular crowding effects on the kinetics of opposing reactions catalyzed by alcohol dehydrogenase. Biochem Biophys Rep 2021; 26:100956. [PMID: 33665382 PMCID: PMC7905371 DOI: 10.1016/j.bbrep.2021.100956] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Revised: 01/03/2021] [Accepted: 02/09/2021] [Indexed: 12/01/2022] Open
Abstract
In order to better understand how the complex, densely packed, heterogeneous milieu of a cell influences enzyme kinetics, we exposed opposing reactions catalyzed by yeast alcohol dehydrogenase (YADH) to both synthetic and protein crowders ranging from 10 to 550 kDa. The results reveal that the effects from macromolecular crowding depend on the direction of the reaction. The presence of the synthetic polymers, Ficoll and dextran, decrease Vmax and Km for ethanol oxidation. In contrast, these crowders have little effect or even increase these kinetic parameters for acetaldehyde reduction. This increase in Vmax is likely due to excluded volume effects, which are partially counteracted by viscosity hindering release of the NAD+ product. Macromolecular crowding is further complicated by the presence of a depletion layer in solutions of dextran larger than YADH, which diminishes the hindrance from viscosity. The disparate effects from 25 g/L dextran or glucose compared to 25 g/L Ficoll or sucrose reveals that soft interactions must also be considered. Data from binary mixtures of glucose, dextran, and Ficoll support this “tuning” of opposing factors. While macromolecular crowding was originally proposed to influence proteins mainly through excluded volume effects, this work compliments the growing body of evidence revealing that other factors, such as preferential hydration, chemical interactions, and the presence of a depletion layer also contribute to the overall effect of crowding. Yeast alcohol dehydrogenase reduction of acetaldehyde is enhanced by crowding. Crowding effects on YADH kinetics depend on the direction of the reaction. Crowders like dextran can be used as a tool to elucidate enzyme mechanism. Excluded volume optimizes YADH hydride transfer; viscosity hinders product release. The presence of a depletion layer with large crowders mitigates their effects.
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Affiliation(s)
- Xander E Wilcox
- Department of Chemistry, University of California at Davis, CA, 95616, USA
| | - Charmaine B Chung
- Department of Chemistry, Hobart and William Smith Colleges, 300 Pulteney St, Geneva, NY, 14456, USA
| | - Kristin M Slade
- Department of Chemistry, Hobart and William Smith Colleges, 300 Pulteney St, Geneva, NY, 14456, USA
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4
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Ozturk TN, Culham DE, Tempelhagen L, Wood JM, Lamoureux G. Salt-Dependent Interactions between the C-Terminal Domain of Osmoregulatory Transporter ProP of Escherichia coli and the Lipid Membrane. J Phys Chem B 2020; 124:8209-8220. [PMID: 32838524 DOI: 10.1021/acs.jpcb.0c03935] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Osmosensing transporter ProP detects the increase in cytoplasmic cation concentration associated with osmotically induced cell dehydration and mediates osmolyte uptake into bacteria. ProP is a 12-transmembrane helix protein with an α-helical, cytoplasmic C-terminal domain (CTD) linked to transmembrane helix XII (TM XII). It has been proposed that the CTD helix associates with the anionic membrane surface to lock ProP in an inactive conformation and that the release of the CTD may activate ProP. To investigate this possible activation mechanism, we have built and simulated a structural model in which the CTD was anchored to the membrane by TM XII and the CTD helix was associated with the membrane surface. Molecular dynamics simulations showed specific intrapeptide salt bridges forming when the CTD associated with the membrane. Experiments supported the presence of the salt bridge Lys447-Asp455 and suggested a role for these residues in osmosensing. Simulations performed at different salt concentrations showed weakened CTD-lipid interactions at 0.25 M KCl and gradual stiffening of the membrane with increasing salinity. These results suggest that salt cations may affect CTD release and activate ProP by increasing the order of membrane phospholipids.
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Affiliation(s)
- Tugba N Ozturk
- Department of Physics, Concordia University, Montreal QC H4B 1R6, Canada.,Centre for Research in Molecular Modeling, Concordia University, Montreal, Quebec H4B 1R6, Canada
| | - Doreen E Culham
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Laura Tempelhagen
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Janet M Wood
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Guillaume Lamoureux
- Centre for Research in Molecular Modeling, Concordia University, Montreal, Quebec H4B 1R6, Canada.,Department of Chemistry and Center for Computational and Integrative Biology, Rutgers University, Camden, New Jersey 08102, United States
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5
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CosR Is a Global Regulator of the Osmotic Stress Response with Widespread Distribution among Bacteria. Appl Environ Microbiol 2020; 86:AEM.00120-20. [PMID: 32169942 DOI: 10.1128/aem.00120-20] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Accepted: 03/10/2020] [Indexed: 12/16/2022] Open
Abstract
Bacteria accumulate small, organic compounds called compatible solutes via uptake from the environment or biosynthesis from available precursors to maintain the turgor pressure of the cell in response to osmotic stress. The halophile Vibrio parahaemolyticus has biosynthesis pathways for the compatible solutes ectoine (encoded by ectABC-asp_ect) and glycine betaine (encoded by betIBA-proXWV), four betaine-carnitine-choline transporters (encoded by bccT1 to bccT4), and a second ProU transporter (encoded by proVWX). All of these systems are osmotically inducible with the exception of bccT2 Previously, it was shown that CosR, a MarR-type regulator, was a direct repressor of ectABC-asp_ect in Vibrio species. In this study, we investigated whether CosR has a broader role in the osmotic stress response. Expression analyses demonstrated that betIBA-proXWV, bccT1, bccT3, bccT4, and proVWX are repressed in low salinity. Examination of an in-frame cosR deletion mutant showed that expression of these systems is derepressed in the mutant at low salinity compared with the wild type. DNA binding assays demonstrated that purified CosR binds directly to the regulatory region of both biosynthesis systems and four transporters. In Escherichia coli green fluorescent protein (GFP) reporter assays, we demonstrated that CosR directly represses transcription of betIBA-proXWV, bccT3, and proVWX Similar to Vibrio harveyi, we showed betIBA-proXWV was directly activated by the quorum-sensing LuxR homolog OpaR, suggesting a conserved mechanism of regulation among Vibrio species. Phylogenetic analysis demonstrated that CosR is ancestral to the Vibrionaceae family, and bioinformatics analysis showed widespread distribution among Gammaproteobacteria in general. Incidentally, in Aliivibrio fischeri, Aliivibrio finisterrensis, Aliivibrio sifiae, and Aliivibrio wodanis, an unrelated MarR-type regulator gene named ectR was clustered with ectABC-asp, which suggests the presence of another novel ectoine biosynthesis regulator. Overall, these data show that CosR is a global regulator of osmotic stress response that is widespread among bacteria.IMPORTANCE Vibrio parahaemolyticus can accumulate compatible solutes via biosynthesis and transport, which allow the cell to survive in high salinity conditions. There is little need for compatible solutes under low salinity conditions, and biosynthesis and transporter systems need to be repressed. However, the mechanism(s) of this repression is not known. In this study, we showed that CosR played a major role in the regulation of multiple compatible solute systems. Phylogenetic analysis showed that CosR is present in all members of the Vibrionaceae family as well as numerous Gammaproteobacteria Collectively, these data establish CosR as a global regulator of the osmotic stress response that is widespread in bacteria, controlling many more systems than previously demonstrated.
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6
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Wilcox XE, Ariola A, Jackson JR, Slade KM. Overlap Concentration and the Effect of Macromolecular Crowding on Citrate Synthase Activity. Biochemistry 2020; 59:1737-1746. [DOI: 10.1021/acs.biochem.0c00073] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Xander E. Wilcox
- Department of Chemistry, University of California at Davis, Davis, California 95616, United States
| | - Ashton Ariola
- Department of Chemistry, Hobart and William Smith Colleges, 300 Pulteney Street, Geneva, New York 14456, United States
| | - Jasmine R. Jackson
- Department of Chemistry, Hobart and William Smith Colleges, 300 Pulteney Street, Geneva, New York 14456, United States
| | - Kristin M. Slade
- Department of Chemistry, Hobart and William Smith Colleges, 300 Pulteney Street, Geneva, New York 14456, United States
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7
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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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8
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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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9
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Christgen SL, Becker DF. Role of Proline in Pathogen and Host Interactions. Antioxid Redox Signal 2019; 30:683-709. [PMID: 29241353 PMCID: PMC6338583 DOI: 10.1089/ars.2017.7335] [Citation(s) in RCA: 65] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Revised: 10/26/2017] [Accepted: 11/14/2017] [Indexed: 01/20/2023]
Abstract
SIGNIFICANCE Proline metabolism has complex roles in a variety of biological processes, including cell signaling, stress protection, and energy production. Proline also contributes to the pathogenesis of various disease-causing organisms. Understanding the mechanisms of how pathogens utilize proline is important for developing new strategies against infectious diseases. Recent Advances: The ability of pathogens to acquire amino acids is critical during infection. Besides protein biosynthesis, some amino acids, such as proline, serve as a carbon, nitrogen, or energy source in bacterial and protozoa pathogens. The role of proline during infection depends on the physiology of the host/pathogen interactions. Some pathogens rely on proline as a critical respiratory substrate, whereas others exploit proline for stress protection. CRITICAL ISSUES Disruption of proline metabolism and uptake has been shown to significantly attenuate virulence of certain pathogens, whereas in other pathogens the importance of proline during infection is not known. Inhibiting proline metabolism and transport may be a useful therapeutic strategy against some pathogens. Developing specific inhibitors to avoid off-target effects in the host, however, will be challenging. Also, potential treatments that target proline metabolism should consider the impact on intracellular levels of Δ1-pyrroline-5-carboxylate, a metabolite intermediate that can have opposing effects on pathogenesis. FUTURE DIRECTIONS Further characterization of how proline metabolism is regulated during infection would provide new insights into the role of proline in pathogenesis. Biochemical and structural characterization of proline metabolic enzymes from different pathogens could lead to new tools for exploring proline metabolism during infection and possibly new therapeutic compounds.
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Affiliation(s)
- Shelbi L. Christgen
- Department of Biochemistry, Redox Biology Center, University of Nebraska−Lincoln, Lincoln, Nebraska
| | - Donald F. Becker
- Department of Biochemistry, Redox Biology Center, University of Nebraska−Lincoln, Lincoln, Nebraska
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10
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Culham DE, Marom D, Boutin R, Garner J, Ozturk TN, Sahtout N, Tempelhagen L, Lamoureux G, Wood JM. Dual Role of the C-Terminal Domain in Osmosensing by Bacterial Osmolyte Transporter ProP. Biophys J 2018; 115:2152-2166. [PMID: 30448037 PMCID: PMC6289098 DOI: 10.1016/j.bpj.2018.10.023] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Revised: 10/22/2018] [Accepted: 10/29/2018] [Indexed: 11/23/2022] Open
Abstract
ProP is a member of the major facilitator superfamily, a proton-osmolyte symporter, and an osmosensing transporter. ProP proteins share extended cytoplasmic carboxyl terminal domains (CTDs) implicated in osmosensing. The CTDs of the best characterized, group A ProP orthologs, terminate in sequences that form intermolecular, antiparallel α-helical coiled coils (e.g., ProPEc, from Escherichia coli). Group B orthologs lack that feature (e.g., ProPXc, from Xanthomonas campestris). ProPXc was expressed and characterized in E. coli to further elucidate the role of the coiled coil in osmosensing. The activity of ProPXc was a sigmoid function of the osmolality in cells and proteoliposomes. ProPEc and ProPXc attained similar activities at the same expression level in E. coli. ProPEc transports proline and glycine betaine with comparable high affinities at low osmolality. In contrast, proline weakly inhibited high-affinity glycine-betaine uptake via ProPXc. The KM for proline uptake via ProPEc increases dramatically with the osmolality. The KM for glycine-betaine uptake via ProPXc did not. Thus, ProPXc is an osmosensing transporter, and the C-terminal coiled coil is not essential for osmosensing. The role of CTD-membrane interaction in osmosensing was examined further. As for ProPEc, the ProPXc CTD co-sedimented with liposomes comprising E. coli phospholipid. Molecular dynamics simulations illustrated association of the monomeric ProPEc CTD with the membrane surface. Comparison with the available NMR structure for the homodimeric coiled coil formed by the ProPEc-CTD suggested that membrane association and homodimeric coiled-coil formation by that peptide are mutually exclusive. The membrane fluidity in liposomes comprising E. coli phospholipid decreased with increasing osmolality in the range relevant for ProP activation. These data support the proposal that ProP activates as cellular dehydration increases cytoplasmic cation concentration, releasing the CTD from the membrane surface. For group A orthologs, this also favors α-helical coiled-coil formation that stabilizes the transporter in an active form.
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Affiliation(s)
- Doreen E Culham
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - David Marom
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Rebecca Boutin
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Jennifer Garner
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada; Centre for Research in Molecular Modeling, Concordia University, Montréal, Québec, Canada
| | - Tugba Nur Ozturk
- Centre for Research in Molecular Modeling, Concordia University, Montréal, Québec, Canada; Department of Physics, Concordia University, Montréal, Québec, Canada
| | - Naheda Sahtout
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Laura Tempelhagen
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - Guillaume Lamoureux
- Centre for Research in Molecular Modeling, Concordia University, Montréal, Québec, Canada; Department of Physics, Concordia University, Montréal, Québec, Canada; Department of Chemistry and Biochemistry, Concordia University, Montréal, Québec, Canada
| | - Janet M Wood
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada.
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11
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Romantsov T, Gonzalez K, Sahtout N, Culham DE, Coumoundouros C, Garner J, Kerr CH, Chang L, Turner RJ, Wood JM. Cardiolipin synthase A colocalizes with cardiolipin and osmosensing transporter ProP at the poles of Escherichia coli cells. Mol Microbiol 2018; 107:623-638. [PMID: 29280215 DOI: 10.1111/mmi.13904] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 11/09/2017] [Accepted: 12/19/2017] [Indexed: 11/29/2022]
Abstract
Osmosensing by transporter ProP is modulated by its cardiolipin (CL)-dependent concentration at the poles of Escherichia coli cells. Other contributors to this phenomenon were sought with the BACterial Two-Hybrid System (BACTH). The BACTH-tagged variants T18-ProP and T25-ProP retained ProP function and localization. Their interaction confirmed the ProP homo-dimerization previously established by protein crosslinking. YdhP, YjbJ and ClsA were prominent among the putative ProP interactors identified by the BACTH system. The functions of YdhP and YjbJ are unknown, although YjbJ is an abundant, osmotically induced, soluble protein. ClsA (CL Synthase A) had been shown to determine ProP localization by mediating CL synthesis. Unlike a deletion of clsA, deletion of ydhP or yjbJ had no effect on ProP localization or function. All three proteins were concentrated at the cell poles, but only ClsA localization was CL-dependent. ClsA was shown to be N-terminally processed and membrane-anchored, with dual, cytoplasmic, catalytic domains. Active site amino acid replacements (H224A plus H404A) inactivated ClsA and compromised ProP localization. YdhP and YjbJ may be ClsA effectors, and interactions of YdhP, YjbJ and ClsA with ProP may reflect their colocalization at the cell poles. Targeted CL synthesis may contribute to the polar localization of CL, ClsA and ProP.
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Affiliation(s)
- Tatyana Romantsov
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - Karen Gonzalez
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - Naheda Sahtout
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - Doreen E Culham
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - Chelsea Coumoundouros
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - Jennifer Garner
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - Craig H Kerr
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
| | - Limei Chang
- Department of Biological Sciences, University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada
| | - Raymond J Turner
- Department of Biological Sciences, University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada
| | - Janet M Wood
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
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12
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Stress Responses, Adaptation, and Virulence of Bacterial Pathogens During Host Gastrointestinal Colonization. Microbiol Spectr 2017; 4. [PMID: 27227312 DOI: 10.1128/microbiolspec.vmbf-0007-2015] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Invading pathogens are exposed to a multitude of harmful conditions imposed by the host gastrointestinal tract and immune system. Bacterial defenses against these physical and chemical stresses are pivotal for successful host colonization and pathogenesis. Enteric pathogens, which are encountered due to the ingestion of or contact with contaminated foods or materials, are highly successful at surviving harsh conditions to colonize and cause the onset of host illness and disease. Pathogens such as Campylobacter, Helicobacter, Salmonella, Listeria, and virulent strains of Escherichia have evolved elaborate defense mechanisms to adapt to the diverse range of stresses present along the gastrointestinal tract. Furthermore, these pathogens contain a multitude of defenses to help survive and escape from immune cells such as neutrophils and macrophages. This chapter focuses on characterized bacterial defenses against pH, osmotic, oxidative, and nitrosative stresses with emphasis on both the direct and indirect mechanisms that contribute to the survival of each respective stress response.
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13
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Diskowski M, Mehdipour AR, Wunnicke D, Mills DJ, Mikusevic V, Bärland N, Hoffmann J, Morgner N, Steinhoff HJ, Hummer G, Vonck J, Hänelt I. Helical jackknives control the gates of the double-pore K + uptake system KtrAB. eLife 2017; 6. [PMID: 28504641 PMCID: PMC5449183 DOI: 10.7554/elife.24303] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2016] [Accepted: 05/14/2017] [Indexed: 12/27/2022] Open
Abstract
Ion channel gating is essential for cellular homeostasis and is tightly controlled. In some eukaryotic and most bacterial ligand-gated K+ channels, RCK domains regulate ion fluxes. Until now, a single regulatory mechanism has been proposed for all RCK-regulated channels, involving signal transduction from the RCK domain to the gating area. Here, we present an inactive ADP-bound structure of KtrAB from Vibrio alginolyticus, determined by cryo-electron microscopy, which, combined with EPR spectroscopy and molecular dynamics simulations, uncovers a novel regulatory mechanism for ligand-induced action at a distance. Exchange of activating ATP to inactivating ADP triggers short helical segments in the K+-translocating KtrB dimer to organize into two long helices that penetrate deeply into the regulatory RCK domains, thus connecting nucleotide-binding sites and ion gates. As KtrAB and its homolog TrkAH have been implicated as bacterial pathogenicity factors, the discovery of this functionally relevant inactive conformation may advance structure-guided drug development. DOI:http://dx.doi.org/10.7554/eLife.24303.001
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Affiliation(s)
- Marina Diskowski
- Institute of Biochemistry, Goethe-University, Frankfurt, Germany
| | - Ahmad Reza Mehdipour
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Frankfurt, Germany
| | - Dorith Wunnicke
- Institute of Biochemistry, Goethe-University, Frankfurt, Germany
| | - Deryck J Mills
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt, Germany
| | | | - Natalie Bärland
- Institute of Biochemistry, Goethe-University, Frankfurt, Germany.,Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt, Germany
| | - Jan Hoffmann
- Institute for Physical and Theoretical Chemistry, Goethe-University, Frankfurt, Germany
| | - Nina Morgner
- Institute for Physical and Theoretical Chemistry, Goethe-University, Frankfurt, Germany
| | | | - Gerhard Hummer
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Frankfurt, Germany.,Institute of Biophysics, Goethe-University, Frankfurt, Germany
| | - Janet Vonck
- Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt, Germany
| | - Inga Hänelt
- Institute of Biochemistry, Goethe-University, Frankfurt, Germany
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14
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van den Berg J, Boersma AJ, Poolman B. Microorganisms maintain crowding homeostasis. Nat Rev Microbiol 2017; 15:309-318. [DOI: 10.1038/nrmicro.2017.17] [Citation(s) in RCA: 131] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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15
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Romantsov T, Culham DE, Caplan T, Garner J, Hodges RS, Wood JM. ProP‐ProP and ProP‐phospholipid interactions determine the subcellular distribution of osmosensing transporter ProP inEscherichia coli. Mol Microbiol 2016; 103:469-482. [DOI: 10.1111/mmi.13569] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/27/2016] [Indexed: 11/30/2022]
Affiliation(s)
- Tatyana Romantsov
- Department of Molecular and Cellular BiologyUniversity of GuelphGuelph ON CanadaN1G2W1
| | - Doreen E. Culham
- Department of Molecular and Cellular BiologyUniversity of GuelphGuelph ON CanadaN1G2W1
| | - Tavia Caplan
- Department of Molecular and Cellular BiologyUniversity of GuelphGuelph ON CanadaN1G2W1
| | - Jennifer Garner
- Department of Molecular and Cellular BiologyUniversity of GuelphGuelph ON CanadaN1G2W1
| | - Robert S. Hodges
- Department of Biochemistry and Molecular GeneticsUniversity of Colorado Denver, School of MedicineP.O. Box 6511, Mail Stop 8101Aurora CO80045, USA
| | - Janet M. Wood
- Department of Molecular and Cellular BiologyUniversity of GuelphGuelph ON CanadaN1G2W1
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16
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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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17
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Abstract
Proline was among the last biosynthetic precursors to have its biosynthetic pathway unraveled. This review recapitulates the findings on the biosynthesis and transport of proline. Glutamyl kinase (GK) catalyzes the ATP-dependent phosphorylation of L-glutamic acid. Purification of γ-GK from Escherichia coli was facilitated by the expression of the proB and proA genes from a high-copy-number plasmid and the development of a specific coupled assay based on the NADPH-dependent reduction of GP by γ-glutamyl phosphate reductase (GPR). GPR catalyzes the NADPH-dependent reduction of GP to GSA. Site directed mutagenesis was used to identify residues that constitute the active site of E. coli GK. This analysis indicated that there is an overlap between the binding sites for glutamate and the allosteric inhibitor proline, suggesting that proline competes with the binding of glutamate. The review also summarizes the genes involved in the metabolism of proline in E. coli and Salmonella. Among the completed genomic sequences of Enterobacteriaceae, genes specifying all three proline biosynthetic enzymes can be discerned in E. coli, Shigella, Salmonella enterica, Serratia marcescens, Erwinia carotovora, Yersinia, Photorhabdus luminescens, and Sodalis glossinidius strain morsitans. The intracellular proline concentration increases with increasing external osmolality in proline-overproducing mutants. This apparent osmotic regulation of proline accumulation in the overproducing strains may be the result of increased retention or recapture of proline, achieved by osmotic stimulation of the ProP or ProU proline transport systems. A number of proline analogs can be incorporated into proteins in vivo or in vitro.
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18
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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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19
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Yu H, Meng X, Aflakpui FWK, Luo L. A salt-induced butA gene of Tetragenococcus halophilus confers salt tolerance to Escherichia coli by heterologous expression of its dual copies. ANN MICROBIOL 2015. [DOI: 10.1007/s13213-015-1160-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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20
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Lang S, Cressatti M, Mendoza KE, Coumoundouros CN, Plater SM, Culham DE, Kimber MS, Wood JM. YehZYXW of Escherichia coli Is a Low-Affinity, Non-Osmoregulatory Betaine-Specific ABC Transporter. Biochemistry 2015; 54:5735-47. [DOI: 10.1021/acs.biochem.5b00274] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Shenhui Lang
- Department
of Molecular and
Cellular Biology, University of Guelph, 488 Gordon Street, Guelph, ON N1G
2W1, Canada
| | - Marisa Cressatti
- Department
of Molecular and
Cellular Biology, University of Guelph, 488 Gordon Street, Guelph, ON N1G
2W1, Canada
| | - Kris E. Mendoza
- Department
of Molecular and
Cellular Biology, University of Guelph, 488 Gordon Street, Guelph, ON N1G
2W1, Canada
| | - Chelsea N. Coumoundouros
- Department
of Molecular and
Cellular Biology, University of Guelph, 488 Gordon Street, Guelph, ON N1G
2W1, Canada
| | - Samantha M. Plater
- Department
of Molecular and
Cellular Biology, University of Guelph, 488 Gordon Street, Guelph, ON N1G
2W1, Canada
| | - Doreen E. Culham
- Department
of Molecular and
Cellular Biology, University of Guelph, 488 Gordon Street, Guelph, ON N1G
2W1, Canada
| | - Matthew S. Kimber
- Department
of Molecular and
Cellular Biology, University of Guelph, 488 Gordon Street, Guelph, ON N1G
2W1, Canada
| | - Janet M. Wood
- Department
of Molecular and
Cellular Biology, University of Guelph, 488 Gordon Street, Guelph, ON N1G
2W1, Canada
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21
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Murdock L, Burke T, Coumoundouros C, Culham DE, Deutch CE, Ellinger J, Kerr CH, Plater SM, To E, Wright G, Wood JM. Analysis of strains lacking known osmolyte accumulation mechanisms reveals contributions of osmolytes and transporters to protection against abiotic stress. Appl Environ Microbiol 2014; 80:5366-78. [PMID: 24951793 PMCID: PMC4136119 DOI: 10.1128/aem.01138-14] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2014] [Accepted: 06/17/2014] [Indexed: 11/20/2022] Open
Abstract
Osmolyte accumulation and release can protect cells from abiotic stresses. In Escherichia coli, known mechanisms mediate osmotic stress-induced accumulation of K(+) glutamate, trehalose, or zwitterions like glycine betaine. Previous observations suggested that additional osmolyte accumulation mechanisms (OAMs) exist and their impacts may be abiotic stress specific. Derivatives of the uropathogenic strain CFT073 and the laboratory strain MG1655 lacking known OAMs were created. CFT073 grew without osmoprotectants in minimal medium with up to 0.9 M NaCl. CFT073 and its OAM-deficient derivative grew equally well in high- and low-osmolality urine pools. Urine-grown bacteria did not accumulate large amounts of known or novel osmolytes. Thus, CFT073 showed unusual osmotolerance and did not require osmolyte accumulation to grow in urine. Yeast extract and brain heart infusion stimulated growth of the OAM-deficient MG1655 derivative at high salinity. Neither known nor putative osmoprotectants did so. Glutamate and glutamine accumulated after growth with either organic mixture, and no novel osmolytes were detected. MG1655 derivatives retaining individual OAMs were created. Their abilities to mediate osmoprotection were compared at 15°C, 37°C without or with urea, and 42°C. Stress protection was not OAM specific, and variations in osmoprotectant effectiveness were similar under all conditions. Glycine betaine and dimethylsulfoniopropionate (DMSP) were the most effective. Trimethylamine-N-oxide (TMAO) was a weak osmoprotectant and a particularly effective urea protectant. The effectiveness of glycine betaine, TMAO, and proline as osmoprotectants correlated with their preferential exclusion from protein surfaces, not with their propensity to prevent protein denaturation. Thus, their effectiveness as stress protectants correlated with their ability to rehydrate the cytoplasm.
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Affiliation(s)
- Lindsay Murdock
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Tangi Burke
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Chelsea Coumoundouros
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Doreen E Culham
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Charles E Deutch
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada School of Mathematical and Natural Sciences, Arizona State University at the West Campus, Phoenix, Arizona, USA
| | - James Ellinger
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Craig H Kerr
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Samantha M Plater
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Eric To
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Geordie Wright
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Janet M Wood
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
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22
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Salinity-dependent impacts of ProQ, Prc, and Spr deficiencies on Escherichia coli cell structure. J Bacteriol 2014; 196:1286-96. [PMID: 24443528 DOI: 10.1128/jb.00827-13] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
ProQ is a cytoplasmic protein with RNA chaperone activities that reside in FinO- and Hfq-like domains. Lesions at proQ decrease the level of the osmoregulatory glycine betaine transporter ProP. Lesions at proQ eliminated ProQ and Prc, the periplasmic protease encoded by the downstream gene prc. They dramatically slowed the growth of Escherichia coli populations and altered the morphologies of E. coli cells in high-salinity medium. ProQ and Prc deficiencies were associated with different phenotypes. ProQ-deficient bacteria were elongated unless glycine betaine was provided. High-salinity cultures of Prc-deficient bacteria included spherical cells with an enlarged periplasm and an eccentric nucleoid. The nucleoid-containing compartment was bounded by the cytoplasmic membrane and peptidoglycan. This phenotype was not evident in bacteria cultivated at low or moderate salinity, nor was it associated with murein lipoprotein (Lpp) deficiency, and it differed from those elicited by the MreB inhibitor A-22 or the FtsI inhibitor aztreonam at low or high salinity. It was suppressed by deletion of spr, which encodes one of three murein hydrolases that are redundantly essential for enlargement of the murein sacculus. Prc deficiency may alter bacterial morphology by impairing control of Spr activity at high salinity. ProQ and Prc deficiencies lowered the ProP activity of bacteria cultivated at moderate salinity by approximately 70% and 30%, respectively, but did not affect other osmoregulatory functions. The effects of ProQ and Prc deficiencies on ProP activity are indirect, reflecting their roles in the maintenance of cell structure.
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23
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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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24
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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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25
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Pilizota T, Shaevitz JW. Fast, multiphase volume adaptation to hyperosmotic shock by Escherichia coli. PLoS One 2012; 7:e35205. [PMID: 22514721 PMCID: PMC3325977 DOI: 10.1371/journal.pone.0035205] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2012] [Accepted: 03/10/2012] [Indexed: 11/25/2022] Open
Abstract
All living cells employ an array of different mechanisms to help them survive changes in extra cellular osmotic pressure. The difference in the concentration of chemicals in a bacterium's cytoplasm and the external environment generates an osmotic pressure that inflates the cell. It is thought that the bacterium Escherichia coli use a number of interconnected systems to adapt to changes in external pressure, allowing them to maintain turgor and live in surroundings that range more than two-hundred-fold in external osmolality. Here, we use fluorescence imaging to make the first measurements of cell volume changes over time during hyperosmotic shock and subsequent adaptation on a single cell level in vivo with a time resolution on the order of seconds. We directly observe two previously unseen phases of the cytoplasmic water efflux upon hyperosmotic shock. Furthermore, we monitor cell volume changes during the post-shock recovery and observe a two-phase response that depends on the shock magnitude. The initial phase of recovery is fast, on the order of 15–20 min and shows little cell-to-cell variation. For large sucrose shocks, a secondary phase that lasts several hours adds to the recovery. We find that cells are able to recover fully from shocks as high as 1 Osmol/kg using existing systems, but that for larger shocks, protein synthesis is required for full recovery.
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Affiliation(s)
- Teuta Pilizota
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey, United States of America
| | - Joshua W. Shaevitz
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey, United States of America
- Department of Physics, Princeton University, Princeton, New Jersey, United States of America
- * E-mail:
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26
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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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27
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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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28
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Peng S, Tasara T, Hummerjohann J, Stephan R. An overview of molecular stress response mechanisms in Escherichia coli contributing to survival of Shiga toxin-producing Escherichia coli during raw milk cheese production. J Food Prot 2011; 74:849-64. [PMID: 21549061 DOI: 10.4315/0362-028x.jfp-10-469] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The ability of foodborne pathogens to survive in certain foods mainly depends on stress response mechanisms. Insight into molecular properties enabling pathogenic bacteria to survive in food is valuable for improvement of the control of pathogens during food processing. Raw milk cheeses are a potential source for human infections with Shiga toxin-producing Escherichia coli (STEC). In this review, we focused on the stress response mechanisms important for allowing STEC to survive raw milk cheese production processes. The major components and regulation pathways for general, acid, osmotic, and heat shock stress responses in E. coli and the implications of these responses for the survival of STEC in raw milk cheeses are discussed.
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Affiliation(s)
- Silvio Peng
- Institute for Food Safety and Hygiene, University of Zurich, Winterthurerstrasse 272, 8057 Zürich, Switzerland
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29
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Chaulk SG, Smith Frieday MN, Arthur DC, Culham DE, Edwards RA, Soo P, Frost LS, Keates RAB, Glover JNM, Wood JM. ProQ is an RNA chaperone that controls ProP levels in Escherichia coli. Biochemistry 2011; 50:3095-106. [PMID: 21381725 DOI: 10.1021/bi101683a] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Transporter ProP mediates osmolyte accumulation in Escherichia coli cells exposed to high osmolality media. The cytoplasmic ProQ protein amplifies ProP activity by an unknown mechanism. The N- and C-terminal domains of ProQ are predicted to be structurally similar to known RNA chaperone proteins FinO and Hfq from E. coli. Here we demonstrate that ProQ is an RNA chaperone, binding RNA and facilitating both RNA strand exchange and RNA duplexing. Experiments performed with the isolated ProQ domains showed that the FinO-like domain serves as a high-affinity RNA-binding domain, whereas the Hfq-like domain is largely responsible for RNA strand exchange and duplexing. These data suggest that ProQ may regulate ProP production. Transcription of proP proceeds from RpoD- and RpoS-dependent promoters. Lesions at proQ affected ProP levels in an osmolality- and growth phase-dependent manner, decreasing ProP levels when proP was expressed from its own chromosomal promoters or from a heterologous plasmid-based promoter. Small RNA molecules are known to regulate cellular levels of sigma factor RpoS. ProQ did not act by changing RpoS levels since proQ lesions did not influence RpoS-dependent stationary phase thermotolerance and they affected ProP production and activity similarly in bacteria without and with an rpoS defect. Taken together, these results suggest that ProQ does not regulate proP transcription. It may act as an RNA-binding protein to regulate proP translation.
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Affiliation(s)
- Steven G Chaulk
- Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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30
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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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Krämer R. Bacterial stimulus perception and signal transduction: response to osmotic stress. CHEM REC 2010; 10:217-29. [PMID: 20607761 DOI: 10.1002/tcr.201000005] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
When exposed to osmotic stress from the environment, bacteria act to maintain cell turgor and hydration by responding both on the level of gene transcription and protein activity. Upon a sudden decrease in external osmolality, internal solutes are released by the action of membrane embedded mechanosensitive channels. In response to an osmotic upshift, the concentration of osmolytes in the cytoplasm is increased both by de novo synthesis and by active uptake. In order to coordinate these processes of osmoregulation, cells are equipped with systems and mechanisms of sensing physical stimuli correlated to changes in the external osmolality (osmosensing), with pathways to transduce these stimuli into useful signals which can be processed in the cell (signal transduction), and mechanisms of regulating proper responses in the cell to recover from the environmental stress and to maintain all necessary physiological functions (osmoregulation). These processes will be described by a number of representative examples, mainly of osmoreactive transport systems with a focus on available data of their molecular mechanism.
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Affiliation(s)
- Reinhard Krämer
- Institute of Biochemistry, University of Cologne, Zülpicher Str. 47, 50674 Cologne, 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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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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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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Culham DE, Romantsov T, Wood JM. Roles of K+, H+, H2O, and DeltaPsi in solute transport mediated by major facilitator superfamily members ProP and LacY. Biochemistry 2008; 47:8176-85. [PMID: 18620422 DOI: 10.1021/bi800794z] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
H (+)-solute symporters ProP and LacY are members of the major facilitator superfamily. ProP mediates osmoprotectant (e.g., proline) accumulation, whereas LacY transports the nutrient lactose. The roles of K (+), H (+), H 2O, and DeltaPsi in H (+)-proline and H (+)-lactose symport were compared using right-side-out cytoplasmic membrane vesicles (MVs) from bacteria expressing both transporters and proteoliposomes (PRLs) reconstituted with pure ProP-His 6. ProP activity increased as LacY activity decreased when osmotic stress (increasing osmolality) was imposed on MVs. The activities of both transporters decreased to similar extents when Na (+) replaced K (+) in MV preparations. Thus, K (+) did not specifically control ProP activity. As with LacY, an increasing extravesicular pH stimulated ProP-mediated proline efflux much more than ProP-mediated proline exchange from de-energized MVs. In contrast to that of LacY, ProP-mediated exchange was only 2-fold faster than ProP-mediated efflux and was inhibited by respiration. In the absence of the protonmotive force (Deltamu H (+) ), efflux of lactose from MVs was much more sensitive to increasing osmolality than lactose exchange. Thus, H 2O may be directly involved in proton transport via LacY. In the absence of Deltamu H (+) , proline efflux and exchange from MVs were osmolality-independent. In PRLs with a DeltapH of 1 (lumen alkaline), ProP-His 6 was inactive when the membrane potential (DeltaPsi) was zero, was active but insensitive to osmolality when DeltaPsi was -100 mV, and became osmolality-sensitive as DeltaPsi increased further to -137 mV. ProP-His 6 had the same membrane orientation in PRLs as in cells and MVs. ProP switches among "off", "on", and "osmolality-sensitive" states as the membrane potential increases. Kinetic parameters determined in the absence of Deltamu H (+) represent a ProP population that is predominantly off.
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Affiliation(s)
- Doreen E Culham
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
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Romantsov T, Stalker L, Culham DE, Wood JM. Cardiolipin controls the osmotic stress response and the subcellular location of transporter ProP in Escherichia coli. J Biol Chem 2008; 283:12314-23. [PMID: 18326496 DOI: 10.1074/jbc.m709871200] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The phospholipid composition of the membrane and transporter structure control the subcellular location and function of osmosensory transporter ProP in Escherichia coli. Growth in media of increasing osmolality increases, and entry to stationary phase decreases, the proportion of phosphatidate in anionic lipids (phosphatidylglycerol (PG) plus cardiolipin (CL)). Both treatments increase the CL:PG ratio. Transporters ProP and LacY are concentrated with CL (and not PG) near cell poles and septa. The polar concentration of ProP is CL-dependent. Here we show that the polar concentration of LacY is CL-independent. The osmotic activation threshold of ProP was directly proportional to the CL content of wild type bacteria, the PG content of CL-deficient bacteria, and the anionic lipid content of cells and proteoliposomes. CL was effective at a lower concentration in cells than in proteoliposomes, and at a much lower concentration than PG in either system. Thus, in wild type bacteria, osmotic induction of CL synthesis and concentration of ProP with CL at the cell poles adjust the osmotic activation threshold of ProP to match ambient conditions. ProP proteins linked by homodimeric, C-terminal coiled-coils are known to activate at lower osmolalities than those without such structures and coiled-coil disrupting mutations raise the osmotic activation threshold. Here we show that these mutations also prevent polar concentration of ProP. Stabilization of the C-terminal coiled-coil by covalent cross-linking of introduced Cys reverses the impact of increasing CL on the osmotic activation of ProP. Association of ProP C termini with the CL-rich membrane at cell poles may raise the osmotic activation threshold by blocking coiled-coil formation. Mutations that block coiled-coil formation may also block association of the C termini with the CL-rich membrane.
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Affiliation(s)
- Tatyana Romantsov
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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Möker N, Reihlen P, Krämer R, Morbach S. Osmosensing Properties of the Histidine Protein Kinase MtrB from. J Biol Chem 2007; 282:27666-77. [PMID: 17650500 DOI: 10.1074/jbc.m701749200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The MtrB-MtrA two component system of Corynebacterium glutamicum was recently shown to be in involved in the osmostress response as well as cell wall metabolism. To address the question of whether the histidine protein kinase MtrB is an osmosensor, the kinase was purified and reconstituted into liposomes in a functionally active form. The activity regulation was investigated by varying systematically physicochemical parameters, which are putative stimuli that could be used by the bacterial cell to detect osmotic conditions. Membrane shrinkage was ruled out as a stimulus for activation of MtrB. Instead, MtrB was shown to be activated upon the addition of various chemical compounds, like sugars, amino acids, and polyethylene glycols. Because of the different chemical nature of the solutes, it seems unlikely that they bind to a specific binding site. Instead, they are proposed to act via a change of the hydration state of the protein shifting MtrB into the active state. For MtrB activation it was essential that these solutes were added at the same side as the cytoplasmic domains of the kinase were located, indicating that hypertonicity is sensed by MtrB via cytoplasmatically located protein domains. This was confirmed by the analysis of two MtrB mutants in which either the large periplasmic loop or the HAMP domain was deleted. These mutants were regulated similar to wild type MtrB. Thus, we postulate that MtrB belongs to a class of histidine protein kinases that sense environmental changes at cytoplasmatic protein domains independently of the periplasmic loop and the cytoplasmic HAMP domain.
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Affiliation(s)
- Nina Möker
- Institut für Biochemie der Universität zu Köln, Zülpicher Strasse 47, 50674 Köln, Germany
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Romantsov T, Helbig S, Culham DE, Gill C, Stalker L, Wood JM. Cardiolipin promotes polar localization of osmosensory transporter ProP in Escherichia coli. Mol Microbiol 2007; 64:1455-65. [PMID: 17504273 DOI: 10.1111/j.1365-2958.2007.05727.x] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The osmolality required to activate osmosensory transporter ProP and the proportion of cardiolipin (CL) among the phospholipids of Escherichia coli rise with growth medium osmolality. Most CL synthesis has been attributed to the cls gene product. Transcription of cls increased with osmolality. The proportion of CL was low and osmolality-independent in cls(-) bacteria. It increased more dramatically on the transition to stationary phase in cls(-) than cls(+) bacteria. Thus, Cls is responsible for osmoregulated CL synthesis and other enzymes may contribute to CL accumulation during stationary phase. The proportion of phosphatidylglycerol (PG) was elevated and it increased with medium osmolality in cls(-) bacteria. A cls defect impaired growth of E. coli on solid and in liquid media at low and, more strongly, at high osmolality. Bacteria cultured at high osmolality without osmoprotectant were shorter and rounder than those cultured at low osmolality or with glycine betaine. Fluorescence microscopy showed that CL and ProP colocalize at the poles and near the septa of dividing E. coli cells. The polar localization of ProP was independent of its expression level but correlated with the proportion and polar localization of CL. Association with CL (and not PG) may be required for polar ProP localization.
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Affiliation(s)
- Tatyana Romantsov
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
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Tøndervik A, Strøm AR. Membrane topology and mutational analysis of the osmotically activated BetT choline transporter of Escherichia coli. Microbiology (Reading) 2007; 153:803-813. [PMID: 17322201 DOI: 10.1099/mic.0.2006/003608-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
For osmoprotection, Escherichia coli can synthesize glycine betaine from externally supplied choline by the Bet system (betTIBA products). The major carrier of choline is the high-affinity, proton-driven, secondary transporter BetT, which belongs to the BCCT family of transporters. Fusion proteins consisting of N-terminal fragments of BetT linked to beta-galactosidase (LacZ) or alkaline phosphatase (PhoA) were constructed. By analysis of 51 fusion proteins with 37 unique fusion-points, the predictions that BetT comprised 12 membrane-spanning regions and that its N- and C-terminal extensions of about 12 and 180 amino acid residues, respectively, were situated in the cytoplasm were confirmed. This is believed to represent the first experimental examination of the membrane topology of a BCCT family protein. Osmotic upshock experiments were performed with spectinomycin-treated E. coli cells that had expressed the wild-type or a mutant BetT protein during growth at low osmolality (160 mosmol kg(-1)). The choline transport activity of wild-type BetT increased tenfold when the cells were stressed with 0.4 M NaCl (total osmolality 780 mosmol kg(-1)). The peak activity was recorded 5 min after the upshock and higher or lower concentrations of NaCl reduced the activity. Deletions of 1-12 C-terminal residues of BetT caused a gradual reduction in the degree of osmotic activation from ten- to twofold. Mutant proteins with deletion of 18-101 residues displayed a background transport activity, but they could not be osmotically activated. The data showed that the cytoplasmic C-terminal domain of BetT plays an important role in the regulation of BetT activity and that C-terminal truncations can cause BetT to be permanently locked in a low-transport-activity mode.
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Affiliation(s)
- Anne Tøndervik
- Department of Biotechnology, The Norwegian University of Science and Technology, N-7491 Trondheim, Norway
| | - Arne R Strøm
- Department of Biotechnology, The Norwegian University of Science and Technology, N-7491 Trondheim, Norway
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Möker N, Krämer J, Unden G, Krämer R, Morbach S. In vitro analysis of the two-component system MtrB-MtrA from Corynebacterium glutamicum. J Bacteriol 2007; 189:3645-9. [PMID: 17293417 PMCID: PMC1855877 DOI: 10.1128/jb.01920-06] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The two-component system MtrBA is involved in the osmostress response of Corynebacterium glutamicum. MtrB was reconstituted in a functionally active form in liposomes and showed autophosphorylation and phosphatase activity. In proteoliposomes, MtrB activity was stimulated by monovalent cations used by many osmosensors for the detection of hypertonicity. Although MtrB was activated by monovalent cations, they lead in vitro to a general stabilization of histidine kinases and do not represent the stimulus for MtrB to sense hyperosmotic stress.
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Affiliation(s)
- Nina Möker
- Institut für Biochemie der Universität zu Köln, Zülpicher Str. 47, D-50674 Köln, Germany
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Abstract
Cells faced with dehydration because of increasing extracellular osmotic pressure accumulate solutes through synthesis or transport. Water follows, restoring cellular hydration and volume. Prokaryotes and eukaryotes possess arrays of osmoregulatory genes and enzymes that are responsible for solute accumulation under osmotic stress. In bacteria, osmosensing transporters can detect increasing extracellular osmotic pressure and respond by mediating the uptake of organic osmolytes compatible with cellular functions ("compatible solutes"). This chapter reviews concepts and methods critical to the identification and study of osmosensing transporters. Like some experimental media, cytoplasm is a "nonideal" solution so the estimation of key solution properties (osmotic pressure, osmolality, water activity, osmolarity, and macromolecular crowding) is essential for studies of osmosensing and osmoregulation. Because bacteria vary widely in osmotolerance, techniques for its characterization provide an essential context for the elucidation of osmosensory and osmoregulatory mechanisms. Powerful genetic, molecular biological, and biochemical tools are now available to aid in the identification and characterization of osmosensory transporters, the genes that encode them, and the osmoprotectants that are their substrates. Our current understanding of osmosensory mechanisms is based on measurements of osmosensory transporter activity performed with intact cells, bacterial membrane vesicles, and proteoliposomes reconstituted with purified transporters. In the quest to elucidate the structural mechanisms of osmosensing and osmoregulation, researchers are now applying the full range of available biophysical, biochemical, and molecular biological tools to osmosensory transporter prototypes.
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Affiliation(s)
- Janet M Wood
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
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Murugova TN, Gordeliy VI, Kuklin AI, Kovalev YS, Yurkov VI, Nurenberg A, Islamov AK, Yaguzhinskii LS. Detection of new double-membrane structures in native mitochondria by the method of small-angle neutron scattering. Biophysics (Nagoya-shi) 2006. [DOI: 10.1134/s0006350906060054] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Abstract
Osmosensors are proteins that sense environmental osmotic pressure. They mediate or direct osmoregulatory responses that allow cells to survive osmotic changes and extremes. Bacterial osmosensing transporters sense high external osmotic pressure and respond by mediating organic osmolyte uptake, hence cellular rehydration. Detailed studies of osmosensing transporters OpuA, BetP, and ProP suggest that they sense and respond to different osmotic pressure-dependent cellular properties. These studies also suggest that each protein has a cytoplasmic osmosensory or osmoregulatory domain, but that these domains differ in structure and function. It is not yet clear whether each transporter represents a distinct osmosensory mechanism or whether different research groups are approaching the same mechanism by way of different paths. Principles emerging from this research will apply to other osmosensors, including those that initiate signal transduction cascades in prokaryotes and eukaryotes.
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Affiliation(s)
- Janet M Wood
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
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Ignatova Z, Gierasch LM. Inhibition of protein aggregation in vitro and in vivo by a natural osmoprotectant. Proc Natl Acad Sci U S A 2006; 103:13357-61. [PMID: 16899544 PMCID: PMC1569168 DOI: 10.1073/pnas.0603772103] [Citation(s) in RCA: 238] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Small organic molecules termed osmolytes are harnessed by a variety of cell types in a wide range of organisms to counter unfavorable physiological conditions that challenge protein stability and function. Using a well characterized reporter system that we developed to allow in vivo observations, we have explored how the osmolyte proline influences the stability and aggregation of a model aggregation-prone protein, P39A cellular retinoic acid-binding protein. Strikingly, we find that the natural osmolyte proline abrogates aggregation both in vitro and in vivo (in an Escherichia coli expression system). Importantly, proline also prevented aggregation of constructs containing exon 1 of huntingtin with extended polyglutamine tracts. Although compatible osmolytes are known to stabilize the native state, our results point to a destabilizing effect of proline on partially folded states and early aggregates and a solubilizing effect on the native state. Because proline is believed to act through a combination of solvophobic backbone interactions and favorable side-chain interactions that are not specific to a particular sequence or structure, the observed effect is likely to be general. Thus, the osmolyte proline may be protective against biomedically important protein aggregates that are hallmarks of several late-onset neurodegenerative diseases including Huntington's, Alzheimer's, and Parkinson's. In addition, these results should be of practical importance because they may enable protein expression at higher efficiency under conditions where aggregation competes with proper folding.
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Affiliation(s)
- Zoya Ignatova
- Departments of *Biochemistry and Molecular Biology and
- Max Planck Institute for Biochemistry, D-82152 Martinsried, Germany
| | - Lila M. Gierasch
- Departments of *Biochemistry and Molecular Biology and
- Chemistry, University of Massachusetts, Amherst, MA 01003; and
- To whom correspondence should be addressed. E-mail:
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Mahmood NABN, Biemans-Oldehinkel E, Patzlaff JS, Schuurman-Wolters GK, Poolman B. Ion specificity and ionic strength dependence of the osmoregulatory ABC transporter OpuA. J Biol Chem 2006; 281:29830-9. [PMID: 16844687 DOI: 10.1074/jbc.m604907200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ATPase subunit of the osmoregulatory ATP-binding cassette transporter OpuA from Lactococcus lactis has a C-terminal extension, the tandem cystathionine beta-synthase (CBS) domain, which constitutes the sensor that allows the transporter to sense and respond to osmotic stress (Biemans-Oldehinkel, E., Mahmood, N. A. B. N., and Poolman, B. (2006) Proc. Natl. Acad. Sci. U. S. A. 103, 10624-10629). C-terminal of the tandem CBS domain is an 18-residue anionic tail (DIPDEDEVEEIEKEEENK). To investigate the ion specificity of the full transporter, we probed the activity of inside-out reconstituted wild-type OpuA and the anionic tail deletion mutant OpuADelta12; these molecules have the tandem CBS domains facing the external medium. At a mole fraction of 40% of anionic lipids in the membrane, the threshold ionic strength for activation of OpuA was approximately 0.15, irrespective of the electrolyte composition of the medium. At equivalent concentrations, bivalent cations (Mg(2+) and Ba(2+)) were more effective in activating OpuA than NH(4)(+), K(+), Na(+), or Li(+), consistent with an ionic strength-based sensing mechanism. Surprisingly, Rb(+) and Cs(+) were potent inhibitors of wild-type OpuA, and 0.1 mM RbCl was sufficient to completely inhibit the transporter even in the presence of 0.2 M KCl. Rb(+) and Cs(+) were no longer inhibitory in OpuADelta12, indicating that the anionic C-terminal tail participates in the formation of a binding site for large alkali metal ions. Compared with OpuADelta12, wild-type OpuA required substantially less potassium ions (the dominant ion under physiological conditions) for activation. Our data lend new support for the contention that the CBS module in OpuA constitutes the ionic strength sensor whose activity is modulated by the C-terminal anionic tail.
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Affiliation(s)
- N A B Nik Mahmood
- Membrane Enzymology Group, Department of Biochemistry, Groningen Biomolecular Science and Biotechnology Institute and Materials Science Centre, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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Biemans-Oldehinkel E, Mahmood NABN, Poolman B. A sensor for intracellular ionic strength. Proc Natl Acad Sci U S A 2006; 103:10624-9. [PMID: 16815971 PMCID: PMC1502282 DOI: 10.1073/pnas.0603871103] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cystathionine-beta-synthase (CBS) domains are found in >4,000 proteins in species from all kingdoms of life, yet their functions are largely unknown. Tandem CBS domains are associated with membrane transport proteins, most notably members of the ATP-binding cassette (ABC) superfamily; voltage-gated chloride channels and transporters; cation efflux systems; and various enzymes, transcription factors, and proteins of unknown function. We now show that tandem CBS domains in the osmoregulatory ABC transporter OpuA are sensors for ionic strength that control the transport activity through an electrostatic switching mechanism. The on/off state of the transporter is determined by the surface charge of the membrane and the internal ionic strength that is sensed by the CBS domains. By modifying the CBS domains, we can control the ionic strength dependence of the transporter: deleting a stretch of C-terminal anionic residues shifts the ionic strength dependence to higher values, whereas deleting the CBS domains makes the system largely independent of ionic strength. We present a model for the gating of membrane transport by ionic strength and propose a new role for CBS domains.
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Affiliation(s)
- Esther Biemans-Oldehinkel
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Nik A. B. N. Mahmood
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Bert Poolman
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
- *To whom correspondence should be addressed. E-mail:
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Tsai CJ, Ziegler C. Structure Determination of Secondary Transport Proteins by Electron Crystallography: Two-Dimensional Crystallization of the Betaine Uptake System BetP. J Mol Microbiol Biotechnol 2006; 10:197-207. [PMID: 16645315 DOI: 10.1159/000091565] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Structure determination at high resolution is still a challenge for membrane proteins in general, but in particular for secondary transporters due to their highly dynamic nature. X-ray structures of ten secondary transporters have recently been determined, but a thorough understanding of transport mechanisms necessitates structures at different functional states. Electron cryo-microscopy of two-dimensional (2D) crystals offers an alternative to obtain structural information at intermediate resolution. Electron crystallography is a sophisticated way to study proteins in a natural membrane environment and to track conformational changes in situ. Furthermore, basic interactions between protein and lipids can be investigated. Projection and 3-dimensional maps of six secondary transporters from different families have been determined by electron crystallography of 2D crystals at a resolution of 8 A and better. In this review, we give an overview about the principles of 2D crystallization, in particular of secondary transporters, and summarize the important steps successfully applied to establish and improve the 2D crystallization of the high-affinity glycine betaine uptake system from Corynebacterium glutamicum, BetP.
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Affiliation(s)
- Ching-Ju Tsai
- Max Planck Institute of Biophysics Frankfurt, Department of Structural Biology, Frankfurt a. Main, Germany
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Morbach S, Krämer R. Structure and Function of the Betaine Uptake System BetP of Corynebacterium glutamicum: Strategies to Sense Osmotic and Chill Stress. J Mol Microbiol Biotechnol 2006; 10:143-53. [PMID: 16645311 DOI: 10.1159/000091561] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The soil bacterium Corynebacterium glutamicum has to cope with frequent fluctuations of the external osmolarity and temperature. The consequences of hyperosmotic and chill stress seem to differ, either causing dehydration of the cytoplasm or leading to impairment of cellular functions due to low temperature. Nevertheless, a particular type of regulatory response, namely the accumulation of so-called compatible solutes, is induced under both conditions. Compatible solutes are known to stabilize the native conformation of enzymes, which may be affected by osmotic and chill stress. BetP is a high-affinity uptake carrier for the compatible solute glycine betaine in C. glutamicum. BetP includes, besides its catalytic function, the ability to sense hyperosmotic conditions and chill stress. As a consequence, the carrier is activated in dependence of the extent of these types of stress. The signal input related to these changes of the environmental conditions is based on at least two different mechanisms. In case of hyperosmotic stress, BetP responds to the internal potassium concentration as a measure for hypertonicity, whereas chill stress is detected by an independent signal, most probably changes of the physical state of the membrane.
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Affiliation(s)
- Susanne Morbach
- Institut für Biochemie der Universität zu Köln, Cologne, Germany.
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Balaji B, O'Connor K, Lucas JR, Anderson JM, Csonka LN. Timing of induction of osmotically controlled genes in Salmonella enterica Serovar Typhimurium, determined with quantitative real-time reverse transcription-PCR. Appl Environ Microbiol 2006; 71:8273-83. [PMID: 16332813 PMCID: PMC1317391 DOI: 10.1128/aem.71.12.8273-8283.2005] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The signals that control the transcription of osmoregulated genes are not understood satisfactorily. The "turgor control model" suggested that the primary osmoregulatory signal in Enterobacteriaceae is turgor loss, which induces the kdp K+ transport operon and activates the Trk K+ permease. The ensuing increase in cytoplasmic K+ concentration was proposed to be the signal that turns on all secondary responses, including the induction of the proU (proline-glycine betaine transport) operon. The "ionic strength model" proposed that the regulatory signal for all osmotically controlled responses is the increase in the cytoplasmic ionic strength or macromolecular crowding after an osmotic upshift. The assumption in the turgor control model that the induction of kdp is a primary response to osmotic shock predicts that this response should precede all secondary responses. Both models predict that the induction of all osmotically activated responses should be independent of the chemical nature of the solute used to impose osmotic stress. We tested these predictions by quantitative real-time reverse transcription-PCR analysis of the expression of six osmotically regulated genes in Salmonella enterica serovar Typhimurium. After shock with 0.3 M NaCl, proU was induced at 4 min, proP and rpoS were induced at 4 to 6 min, kdp was induced at 8 to 9 min, and otsB and ompC were induced at 10 to 12 min. After an equivalent osmotic shock with 0.6 M sucrose, proU was induced with kinetics similar to those seen with NaCl, but induction of kdp was reduced 150-fold in comparison to induction by NaCl. Our results are inconsistent with both the turgor control and the ionic strength control models.
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Affiliation(s)
- Boovaraghan Balaji
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392, USA
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