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Green VE, Klancher CA, Yamamoto S, Dalia AB. The molecular mechanism for carbon catabolite repression of the chitin response in Vibrio cholerae. PLoS Genet 2023; 19:e1010767. [PMID: 37172034 PMCID: PMC10208484 DOI: 10.1371/journal.pgen.1010767] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 05/24/2023] [Accepted: 04/30/2023] [Indexed: 05/14/2023] Open
Abstract
Vibrio cholerae is a facultative pathogen that primarily occupies marine environments. In this niche, V. cholerae commonly interacts with the chitinous shells of crustacean zooplankton. As a chitinolytic microbe, V. cholerae degrades insoluble chitin into soluble oligosaccharides. Chitin oligosaccharides serve as both a nutrient source and an environmental cue that induces a strong transcriptional response in V. cholerae. Namely, these oligosaccharides induce the chitin sensor, ChiS, to activate the genes required for chitin utilization and horizontal gene transfer by natural transformation. Thus, interactions with chitin impact the survival of V. cholerae in marine environments. Chitin is a complex carbon source for V. cholerae to degrade and consume, and the presence of more energetically favorable carbon sources can inhibit chitin utilization. This phenomenon, known as carbon catabolite repression (CCR), is mediated by the glucose-specific Enzyme IIA (EIIAGlc) of the phosphoenolpyruvate-dependent phosphotransferase system (PTS). In the presence of glucose, EIIAGlc becomes dephosphorylated, which inhibits ChiS transcriptional activity by an unknown mechanism. Here, we show that dephosphorylated EIIAGlc interacts with ChiS. We also isolate ChiS suppressor mutants that evade EIIAGlc-dependent repression and demonstrate that these alleles no longer interact with EIIAGlc. These findings suggest that EIIAGlc must interact with ChiS to exert its repressive effect. Importantly, the ChiS suppressor mutations we isolated also relieve repression of chitin utilization and natural transformation by EIIAGlc, suggesting that CCR of these behaviors is primarily regulated through ChiS. Together, our results reveal how nutrient conditions impact the fitness of an important human pathogen in its environmental reservoir.
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Affiliation(s)
- Virginia E. Green
- Department of Biology, Indiana University, Bloomington, Indiana, United States of America
| | - Catherine A. Klancher
- Department of Biology, Indiana University, Bloomington, Indiana, United States of America
| | - Shouji Yamamoto
- Department of Bacteriology I, National Institute of Infectious Diseases, Tokyo, Japan
| | - Ankur B. Dalia
- Department of Biology, Indiana University, Bloomington, Indiana, United States of America
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2
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Bistability and Nonmonotonic Induction of the lac Operon in the Natural Lactose Uptake System. Biophys J 2017; 112:1984-1996. [PMID: 28494968 DOI: 10.1016/j.bpj.2017.03.038] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Revised: 02/22/2017] [Accepted: 03/31/2017] [Indexed: 11/23/2022] Open
Abstract
The Escherichia coli lac operon is regulated by a positive feedback loop whose potential to generate an all-or-none response in single cells has been a paradigm for bistable gene expression. However, so far bistable lac induction has only been observed using gratuitous inducers, raising the question about the biological relevance of bistable lac induction in the natural setting with lactose as the inducer. In fact, the existing experimental evidence points to a graded rather than an all-or-none response in the natural lactose uptake system. In contrast, predictions based on computational models of the lactose uptake pathway remain controversial. Although some argue in favor of bistability, others argue against it. Here, we reinvestigate lac operon expression in single cells using a combined experimental/modeling approach. To this end, we parameterize a well-supported mathematical model using transient measurements of LacZ activity upon induction with different amounts of lactose. The resulting model predicts a monostable induction curve for the wild-type system, but indicates that overexpression of the LacI repressor would drive the system into the bistable regime. Both predictions were confirmed experimentally supporting the view that the wild-type lac induction circuit generates a graded response rather than bistability. More interestingly, we find that the lac induction curve exhibits a pronounced maximum at intermediate lactose concentrations. Supported by our data, a model-based analysis suggests that the nonmonotonic response results from saturation of the LacI repressor at low inducer concentrations and dilution of Lac enzymes due to an increased growth rate beyond the saturation point. We speculate that the observed maximum in the lac expression level helps to save cellular resources by limiting Lac enzyme expression at high inducer concentrations.
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3
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Saier MH, Zhang Z. Control of Transposon-Mediated Directed Mutation by the Escherichia coli Phosphoenolpyruvate:Sugar Phosphotransferase System. J Mol Microbiol Biotechnol 2015; 25:226-33. [PMID: 26159081 DOI: 10.1159/000375375] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The phosphoenolpyruvate:sugar phosphotransferase system (PTS) has been shown to control transport, cell metabolism and gene expression. We here present results supporting the novel suggestion that in certain instances it also regulates the mutation rate. Directed mutations are defined as mutations that occur at higher frequencies when beneficial than when neutral or detrimental. To date, the occurrence of directed point mutations has not been documented and confirmed, but a few examples of transposon-mediated directed mutations have been reported. Here we focus on the first and best-studied example of directed mutation, which involves the regulation of insertion sequence-5 hopping into a specific site upstream of the glpFK glycerol utilization operon in Escherichia coli. This insertional event specifically activates expression of the glpFK operon, allowing the growth of wild-type cells with glycerol as a carbon source in the presence of nonmetabolizable glucose analogues which normally block glycerol utilization. The sugar-transporting PTS controls this process by regulating levels of cytoplasmic glycerol-3-phosphate and cyclic (c)AMP as established in previous publications. Direct involvement of the glycerol repressor, GlpR, and the cAMP receptor protein, Crp, in the regulation of transposon-mediated directed mutation has been demonstrated.
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Affiliation(s)
- Milton H Saier
- Department of Molecular Biology, Division of Biological Sciences, University of California at San Diego, La Jolla, Calif., USA
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4
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Thermodynamic mechanism for inhibition of lactose permease by the phosphotransferase protein IIAGlc. Proc Natl Acad Sci U S A 2015; 112:2407-12. [PMID: 25675534 DOI: 10.1073/pnas.1500891112] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In a variety of bacteria, the phosphotransferase protein IIA(Glc) plays a key regulatory role in catabolite repression in addition to its role in the vectorial phosphorylation of glucose catalyzed by the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS). The lactose permease (LacY) of Escherichia coli catalyzes stoichiometric symport of a galactoside with an H(+), using a mechanism in which sugar- and H(+)-binding sites become alternatively accessible to either side of the membrane. Both the expression (via regulation of cAMP levels) and the activity of LacY are subject to regulation by IIA(Glc) (inducer exclusion). Here we report the thermodynamic features of the IIA(Glc)-LacY interaction as measured by isothermal titration calorimetry (ITC). The studies show that IIA(Glc) binds to LacY with a Kd of about 5 μM and a stoichiometry of unity and that binding is driven by solvation entropy and opposed by enthalpy. Upon IIA(Glc) binding, the conformational entropy of LacY is restrained, which leads to a significant decrease in sugar affinity. By suppressing conformational dynamics, IIA(Glc) blocks inducer entry into cells and favors constitutive glucose uptake and utilization. Furthermore, the studies support the notion that sugar binding involves an induced-fit mechanism that is inhibited by IIA(Glc) binding. The precise mechanism of the inhibition of LacY by IIA(Glc) elucidated by ITC differs from the inhibition of melibiose permease (MelB), supporting the idea that permeases can differ in their thermodynamic response to binding IIA(Glc).
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Shin D, Cho N, Kim YJ, Seok YJ, Ryu S. Up-regulation of the cellular level of Escherichia coli PTS components by stabilizing reduced transcripts of the genes in response to the low oxygen level. Biochem Biophys Res Commun 2008; 370:609-12. [PMID: 18402772 DOI: 10.1016/j.bbrc.2008.03.145] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2008] [Accepted: 03/31/2008] [Indexed: 10/22/2022]
Abstract
When Escherichia coli cells were grown with limited levels of oxygen, the glucose-induced transcription of ptsG was decreased whereas deletion of the arcA gene partially restored it, which was consistent with the previous report that the ArcA protein represses ptsG transcription. However, under this circumstance, we found that the level of EIICB(Glc) protein encoded by the ptsG gene was rather increased. This paradoxical phenomenon can be explained by the delayed turnover of ptsG mRNA in cells anaerobically grown in the presence of glucose. Finally, our data showed that anaerobic expression of the ptsHIcrr operon is also enhanced by increasing the longevity of the reduced mRNA levels.
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Affiliation(s)
- Dongwoo Shin
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea
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6
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Deutscher J, Francke C, Postma PW. How phosphotransferase system-related protein phosphorylation regulates carbohydrate metabolism in bacteria. Microbiol Mol Biol Rev 2007; 70:939-1031. [PMID: 17158705 PMCID: PMC1698508 DOI: 10.1128/mmbr.00024-06] [Citation(s) in RCA: 985] [Impact Index Per Article: 57.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The phosphoenolpyruvate(PEP):carbohydrate phosphotransferase system (PTS) is found only in bacteria, where it catalyzes the transport and phosphorylation of numerous monosaccharides, disaccharides, amino sugars, polyols, and other sugar derivatives. To carry out its catalytic function in sugar transport and phosphorylation, the PTS uses PEP as an energy source and phosphoryl donor. The phosphoryl group of PEP is usually transferred via four distinct proteins (domains) to the transported sugar bound to the respective membrane component(s) (EIIC and EIID) of the PTS. The organization of the PTS as a four-step phosphoryl transfer system, in which all P derivatives exhibit similar energy (phosphorylation occurs at histidyl or cysteyl residues), is surprising, as a single protein (or domain) coupling energy transfer and sugar phosphorylation would be sufficient for PTS function. A possible explanation for the complexity of the PTS was provided by the discovery that the PTS also carries out numerous regulatory functions. Depending on their phosphorylation state, the four proteins (domains) forming the PTS phosphorylation cascade (EI, HPr, EIIA, and EIIB) can phosphorylate or interact with numerous non-PTS proteins and thereby regulate their activity. In addition, in certain bacteria, one of the PTS components (HPr) is phosphorylated by ATP at a seryl residue, which increases the complexity of PTS-mediated regulation. In this review, we try to summarize the known protein phosphorylation-related regulatory functions of the PTS. As we shall see, the PTS regulation network not only controls carbohydrate uptake and metabolism but also interferes with the utilization of nitrogen and phosphorus and the virulence of certain pathogens.
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Affiliation(s)
- Josef Deutscher
- Microbiologie et Génétique Moléculaire, INRA-CNRS-INA PG UMR 2585, Thiverval-Grignon, France.
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Lee CR, Cho SH, Yoon MJ, Peterkofsky A, Seok YJ. Escherichia coli enzyme IIANtr regulates the K+ transporter TrkA. Proc Natl Acad Sci U S A 2007; 104:4124-9. [PMID: 17289841 PMCID: PMC1794712 DOI: 10.1073/pnas.0609897104] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The maintenance of ionic homeostasis in response to changes in the environment is essential for all living cells. Although there are still many important questions concerning the role of the major monovalent cation K(+), cytoplasmic K(+) in bacteria is required for diverse processes. Here, we show that enzyme IIA(Ntr) (EIIA(Ntr)) of the nitrogen-metabolic phosphotransferase system interacts with and regulates the Escherichia coli K(+) transporter TrkA. Previously we reported that an E. coli K-12 mutant in the ptsN gene encoding EIIA(Ntr) was extremely sensitive to growth inhibition by leucine or leucine-containing peptides (LCPs). This sensitivity was due to the requirement of the dephosphorylated form of EIIA(Ntr) for the derepression of ilvBN expression. Whereas the ptsN mutant is extremely sensitive to LCPs, a ptsN trkA double mutant is as resistant as WT. Furthermore, the sensitivity of the ptsN mutant to LCPs decreases as the K(+) level in culture media is lowered. We demonstrate that dephosphorylated EIIA(Ntr), but not its phosphorylated form, forms a tight complex with TrkA that inhibits the accumulation of high intracellular concentrations of K(+). High cellular K(+) levels in a ptsN mutant promote the sensitivity of E. coli K-12 to leucine or LCPs by inhibiting both the expression of ilvBN and the activity of its gene products. Here, we delineate the similarity of regulatory mechanisms for the paralogous carbon and nitrogen phosphotransferase systems. Dephosphorylated EIIA(Glc) regulates a variety of transport systems for carbon sources, whereas dephosphorylated EIIA(Ntr) regulates the transport system for K(+), which has global effects related to nitrogen metabolism.
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Affiliation(s)
- Chang-Ro Lee
- *Laboratory of Macromolecular Interactions, Department of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea; and
| | - Seung-Hyon Cho
- *Laboratory of Macromolecular Interactions, Department of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea; and
| | - Mi-Jeong Yoon
- *Laboratory of Macromolecular Interactions, Department of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea; and
| | - Alan Peterkofsky
- Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892
| | - Yeong-Jae Seok
- *Laboratory of Macromolecular Interactions, Department of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea; and
- To whom correspondence should be addressed. E-mail:
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8
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Affiliation(s)
- Alan Peterkofsky
- Laboratory of Cell Biology, National Heart, Lung and Blood Institute, Bethesda, MD 20892-8017, USA.
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9
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Lee CR, Koo BM, Cho SH, Kim YJ, Yoon MJ, Peterkofsky A, Seok YJ. Requirement of the dephospho-form of enzyme IIANtr for derepression of Escherichia coli K-12 ilvBN expression. Mol Microbiol 2005; 58:334-44. [PMID: 16164569 DOI: 10.1111/j.1365-2958.2005.04834.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
While the proteins of the phosphoenolpyruvate:carbohydrate phosphotransferase system (carbohydrate PTS) have been shown to regulate numerous targets, little such information is available for the nitrogen-metabolic phosphotransferase system (nitrogen-metabolic PTS). To elucidate the physiological role of the nitrogen-metabolic PTS, we carried out phenotype microarray (PM) analysis with Escherichia coli K-12 strain MG1655 deleted for the ptsP gene encoding the first enzyme of the nitrogen-metabolic PTS. Together with the PM data, growth studies revealed that a ptsN (encoding enzyme IIA(Ntr)) mutant became extremely sensitive to leucine-containing peptides (LCPs), while both ptsP (encoding enzyme I(Ntr)) and ptsO (encoding NPr) mutants were more resistant than wild type. The toxicity of LCPs was found to be due to leucine and the dephospho-form of enzyme IIA(Ntr) was found to be necessary to neutralize leucine toxicity. Further studies showed that the dephospho-form of enzyme IIA(Ntr) is required for derepression of the ilvBN operon encoding acetohydroxy acid synthase I catalysing the first step common to the biosynthesis of the branched-chain amino acids.
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Affiliation(s)
- Chang-Ro Lee
- Laboratory of Macromolecular Interactions, Department of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea
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10
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Karim S, Lundh D, Holmström KO, Mandal A, Pirhonen M. Structural and functional characterization of AtPTR3, a stress-induced peptide transporter of Arabidopsis. J Mol Model 2005; 11:226-36. [PMID: 15889294 DOI: 10.1007/s00894-005-0257-6] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2004] [Accepted: 01/27/2005] [Indexed: 10/25/2022]
Abstract
A T-DNA tagged mutant line of Arabidopsis thaliana, produced with a promoter trap vector carrying a promoterless gus (uidA) as a reporter gene, showed GUS induction in response to mechanical wounding. Cloning of the chromosomal DNA flanking the T-DNA revealed that the insert had caused a knockout mutation in a PTR-type peptide transporter gene named At5g46050 in GenBank, here renamed AtPTR3. The gene and the deduced protein were characterized by molecular modelling and bioinformatics. Molecular modelling of the protein with fold recognition identified 12 transmembrane spanning regions and a large loop between the sixth and seventh helices. The structure of AtPTR3 resembled the other PTR-type transporters of plants and transporters in the major facilitator superfamily. Computer analysis of the AtPTR3 promoter suggested its expression in roots, leaves and seeds, complex hormonal regulation and induction by abiotic and biotic stresses. The computer-based hypotheses were tested experimentally by exposing the mutant plants to amino acids and several stress treatments. The AtPTR3 gene was induced by the amino acids histidine, leucine and phenylalanine in cotyledons and lower leaves, whereas a strong induction was obtained in the whole plant upon exposure to salt. Furthermore, the germination frequency of the mutant line was reduced on salt-containing media, suggesting that the AtPTR3 protein is involved in stress tolerance in seeds during germination.
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Affiliation(s)
- Sazzad Karim
- School of Life Sciences, University of Skövde, 541 28 Skövde, Sweden
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11
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Jeong JY, Kim YJ, Cho N, Shin D, Nam TW, Ryu S, Seok YJ. Expression of ptsG encoding the major glucose transporter is regulated by ArcA in Escherichia coli. J Biol Chem 2004; 279:38513-8. [PMID: 15252051 DOI: 10.1074/jbc.m406667200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Because the phosphoenolpyruvate:sugar phosphotransferase system plays multiple regulatory roles in addition to the phosphorylation-coupled transport of many sugars in bacteria, synthesis of its protein components is regulated in a highly sophisticated way. Thus far, the cAMP receptor protein (CRP) complex and Mlc are known to be the major regulators of ptsHIcrr and ptsG expression in response to the availability of carbon sources. In this report, we performed ligand fishing experiments by using the promoters of ptsHIcrr and ptsG as bait to find out new factors involved in the transcriptional regulation of the phosphoenolpyruvate:sugar phosphotransferase system in Escherichia coli, and we found that the anaerobic regulator ArcA specifically binds to the promoters. Deletion of the arcA gene caused about a 2-fold increase in the ptsG expression, and overexpression of ArcA significantly decreased glucose consumption. In vitro transcription assays showed that phospho-ArcA (ArcA-P) represses ptsG P1 transcription. DNase I footprinting experiments revealed that ArcA-P binds to three sites upstream of the ptsG P1 promoter, two of which overlap the CRP-binding sites, and the ArcA-P binding decreases the CRP binding that is essential for the ptsG P1 transcription. These results suggest that the response regulator ArcA regulates expression of enzyme IICB(Glc) mediating the first step of glucose metabolism in response to the redox conditions of growth in E. coli.
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Affiliation(s)
- Jin-Young Jeong
- Laboratory of Macromolecular Interactions, School of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea
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12
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The bacterial phosphotransferase system: a perfect link of sugar transport and signal transduction. ACTA ACUST UNITED AC 2004. [DOI: 10.1007/b95776] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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13
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Nam TW, Cho SH, Shin D, Kim JH, Jeong JY, Lee JH, Roe JH, Peterkofsky A, Kang SO, Ryu S, Seok YJ. The Escherichia coli glucose transporter enzyme IICB(Glc) recruits the global repressor Mlc. EMBO J 2001; 20:491-8. [PMID: 11157755 PMCID: PMC133465 DOI: 10.1093/emboj/20.3.491] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In addition to effecting the catalysis of sugar uptake, the bacterial phosphoenolpyruvate:sugar phosphotransferase system regulates a variety of physiological processes. Exposure of cells to glucose can result in repression or induction of gene expression. While the mechanism for carbon catabolite repression by glucose was well documented, that for glucose induction was not clearly understood in Escherichia coli. Recently, glucose induction of several E.coli genes has been shown to be mediated by the global repressor Mlc. Here, we elucidate a general mechanism for glucose induction of gene expression in E.coli, revealing a novel type of regulatory circuit for gene expression mediated by the phosphorylation state-dependent interaction of a membrane-bound protein with a repressor. The dephospho-form of enzyme IICB(Glc), but not its phospho-form, interacts directly with Mlc and induces transcription of Mlc-regulated genes by displacing Mlc from its target sequences. Therefore, the glucose induction of Mlc-regulated genes is caused by dephosphorylation of the membrane-bound transporter enzyme IICB(Glc), which directly recruits Mlc to derepress its regulon.
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Affiliation(s)
| | | | - Dongwoo Shin
- School of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742,
School of Agricultural Biotechnology, Seoul National University, Suwon 441-744, Korea and Laboratory of Biochemical Genetics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA Corresponding author e-mail: T.-W.Nam, S.-H.Cho and D.Shin contributed equally to this work
| | | | | | | | | | - Alan Peterkofsky
- School of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742,
School of Agricultural Biotechnology, Seoul National University, Suwon 441-744, Korea and Laboratory of Biochemical Genetics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA Corresponding author e-mail: T.-W.Nam, S.-H.Cho and D.Shin contributed equally to this work
| | | | - Sangryeol Ryu
- School of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742,
School of Agricultural Biotechnology, Seoul National University, Suwon 441-744, Korea and Laboratory of Biochemical Genetics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA Corresponding author e-mail: T.-W.Nam, S.-H.Cho and D.Shin contributed equally to this work
| | - Yeong-Jae Seok
- School of Biological Sciences and Institute of Microbiology, Seoul National University, Seoul 151-742,
School of Agricultural Biotechnology, Seoul National University, Suwon 441-744, Korea and Laboratory of Biochemical Genetics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA Corresponding author e-mail: T.-W.Nam, S.-H.Cho and D.Shin contributed equally to this work
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14
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Weinglass AB, Kaback HR. The central cytoplasmic loop of the major facilitator superfamily of transport proteins governs efficient membrane insertion. Proc Natl Acad Sci U S A 2000; 97:8938-43. [PMID: 10880570 PMCID: PMC16800 DOI: 10.1073/pnas.140224497] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Deletion of 5 residues (Delta5) from the central cytoplasmic loop of the lactose permease of Escherichia coli has no significant effect on expression or activity, whereas Delta12 leads to increased rates of permease turnover after membrane insertion and decreased transport activity, and Delta20 abolishes insertion and activity. By expressing Delta12 or Delta20 in two halves, both expression and activity are restored to levels approximating wild type. Replacing deleted residues with random hydrophilic amino acids also leads to full recovery. However, introduction of hydrophobic residues decreases expression and activity in a context-dependent manner. Thus, a minimum length of the central cytoplasmic loop is vital for proper insertion, stability, and efficient transport activity, because of constraints at the cytoplasmic ends of helices VI and VII. Furthermore, the results are consistent with the idea that the middle cytoplasmic loop provides a temporal delay between insertion of the first six helices into the membrane before insertion of the second six helices.
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Affiliation(s)
- A B Weinglass
- Howard Hughes Medical Institute, Departments of Physiology and Microbiology and Molecular Genetics, Molecular Biology Institute, University of California, Los Angeles, CA 90095-1662, USA
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15
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Forde BG. Nitrate transporters in plants: structure, function and regulation. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1465:219-35. [PMID: 10748256 DOI: 10.1016/s0005-2736(00)00140-1] [Citation(s) in RCA: 262] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Physiological studies have established that plants acquire their NO(-3) from the soil through the combined activities of a set of high- and low-affinity NO(-3) transport systems, with the influx of NO(-3) being driven by the H(+) gradient across the plasma membrane. Some of these NO(-3) transport systems are constitutively expressed, while others are NO(-3)-inducible and subject to negative feedback regulation by the products of NO(-3) assimilation. Here we review recent progress in the characterisation of the two families of NO(-3) transporters that have so far been identified in plants, their structure and their regulation, and consider the evidence for their roles in NO(-3) acquisition. We also discuss what is currently known about the genetic basis of NO(-3) induction and feedback repression of the NO(-3) transport and assimilatory pathway in higher plants.
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Affiliation(s)
- B G Forde
- Biochemistry and Physiology Department, IACR-Rothamsted, Harpenden, UK.
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16
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Kim SY, Nam TW, Shin D, Koo BM, Seok YJ, Ryu S. Purification of Mlc and analysis of its effects on the pts expression in Escherichia coli. J Biol Chem 1999; 274:25398-402. [PMID: 10464268 DOI: 10.1074/jbc.274.36.25398] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Products of the pts operon of Escherichia coli have multiple physiological roles such as sugar transport, and the operon is controlled by two promoters, P0 and P1. Expression of the pts P0 promoter that is increased during growth in the presence of glucose is also activated by cAMP receptor protein.cAMP. Based on the existence of a sequence that has a high similarity with the known Mlc binding site in the promoter, the effects of the Mlc protein on the pts P0 promoter expression were studied. In vivo transcription assays using wild type and mlc-negative E. coli strains grown in the presence and absence of glucose indicate that Mlc negatively regulates expression of the P0 promoter, and Mlc-dependent repression is relieved by glucose in the growth medium. In vitro transcription assay using purified recombinant Mlc showed that Mlc repressed transcription from the P0 but did not affect the activity of the P1. DNase I footprinting experiments revealed that a Mlc binding site was located around +1 to +25 of the promoter and that Mlc inhibited the binding of RNA polymerase to the P0 promoter. Cells overexpressing Mlc showed a very slow fermentation rate compared with the wild type when grown in the presence of various phosphoenolpyruvate-carbohydrate phosphotransferase system sugars but few differences in the presence of non-phosphoenolpyruvate-carbohydrate phosphotransferase system sugars except maltose. These results suggest that the pts operon is one of major targets for the negative regulation by Mlc, and thus Mlc regulates the utilization of various sugars as well as glucose in E. coli. The possibility that the inducer of Mlc may not be sugar or its derivative but an unknown factor is proposed to explain the Mlc induction mechanism by various sugars.
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Affiliation(s)
- S Y Kim
- Department of Microbiology, College of Medicine, Chungbuk National University, Chongju, 361-763 Korea
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17
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Sondej M, Sun J, Seok YJ, Kaback HR, Peterkofsky A. Deduction of consensus binding sequences on proteins that bind IIAGlc of the phosphoenolpyruvate:sugar phosphotransferase system by cysteine scanning mutagenesis of Escherichia coli lactose permease. Proc Natl Acad Sci U S A 1999; 96:3525-30. [PMID: 10097069 PMCID: PMC22326 DOI: 10.1073/pnas.96.7.3525] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mediated by the protein IIAGlc, the phosphoenolpyruvate:sugar phosphotransferase system plays a role in the regulation of activity of other sugar transport systems in Escherichia coli. By using a direct binding assay, a collection of single-Cys replacement mutants in cytoplasmic loops of lactose permease were evaluated for their capacity to bind IIAGlc. Selected Cys replacements in loops IV/V or VI/VII result in loss of binding activity. Analysis of the mutagenesis results together with multiple sequence alignments of a family of proteins that interacts with IIAGlc provides the basis for developing two regions of consensus sequence in those partner proteins necessary for binding to IIAGlc. The requirement for two interaction regions is interpreted in the regulatory framework of a substrate-dependent conformational change that brings those two regions into an orientation optimal for binding IIAGlc.
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Affiliation(s)
- M Sondej
- Laboratory of Biochemical Genetics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
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