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Structural basis of resistance to herbicides that target acetohydroxyacid synthase. Nat Commun 2022; 13:3368. [PMID: 35690625 PMCID: PMC9188596 DOI: 10.1038/s41467-022-31023-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2022] [Accepted: 05/27/2022] [Indexed: 01/02/2023] Open
Abstract
Acetohydroxyacid synthase (AHAS) is the target for more than 50 commercial herbicides; first applied to crops in the 1980s. Since then, 197 site-of-action resistance isolates have been identified in weeds, with mutations at P197 and W574 the most prevalent. Consequently, AHAS is at risk of not being a useful target for crop protection. To develop new herbicides, a functional understanding to explain the effect these mutations have on activity is required. Here, we show that these mutations can have two effects (i) to reduce binding affinity of the herbicides and (ii) to abolish time-dependent accumulative inhibition, critical to the exceptional effectiveness of this class of herbicide. In the two mutants, conformational changes occur resulting in a loss of accumulative inhibition by most herbicides. However, bispyribac, a bulky herbicide is able to counteract the detrimental effects of these mutations, explaining why no site-of-action resistance has yet been reported for this herbicide. Acetohydroxyacid synthase (AHAS) is the target of more than 50 commercial herbicides, with many site-of-action resistance isolates identified in weeds. Here, the authors report the structural and kinetic characterizations to explain the effect AHAS mutations have on herbicide potency.
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2
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Hollóczki O. The Mechanism of N-Heterocyclic Carbene Organocatalysis through a Magnifying Glass. Chemistry 2020; 26:4885-4894. [PMID: 31797448 PMCID: PMC7187225 DOI: 10.1002/chem.201903021] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Indexed: 11/11/2022]
Abstract
The term "N-Heterocyclic carbene organocatalysis" is often invoked in organic synthesis for reactions that are catalyzed by different azolium salts in the presence of bases. Although the mechanism of these reactions is considered today evident, a closer look into the details that have been collected throughout the last century reveals that there are many open questions and even contradictions in the field. Emerging new theoretical and experimental results offer solutions to these problems, because they show that through considering alternative reaction mechanisms a more consistent picture on the catalytic process can be obtained. These novel perspectives will be able to extend the scope of the reactions that we call today N-heterocyclic carbene organocatalysis.
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Affiliation(s)
- Oldamur Hollóczki
- Mulliken Center for Theoretical ChemistryUniversity of BonnBeringstrasse 4+653115BonnGermany
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3
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Structural insights into the mechanism of inhibition of AHAS by herbicides. Proc Natl Acad Sci U S A 2018; 115:E1945-E1954. [PMID: 29440497 DOI: 10.1073/pnas.1714392115] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Acetohydroxyacid synthase (AHAS), the first enzyme in the branched amino acid biosynthesis pathway, is present only in plants and microorganisms, and it is the target of >50 commercial herbicides. Penoxsulam (PS), which is a highly effective broad-spectrum AHAS-inhibiting herbicide, is used extensively to control weed growth in rice crops. However, the molecular basis for its inhibition of AHAS is poorly understood. This is despite the availability of structural data for all other classes of AHAS-inhibiting herbicides. Here, crystallographic data for Saccharomyces cerevisiae AHAS (2.3 Å) and Arabidopsis thaliana AHAS (2.5 Å) in complex with PS reveal the extraordinary molecular mechanisms that underpin its inhibitory activity. The structures show that inhibition of AHAS by PS triggers expulsion of two molecules of oxygen bound in the active site, releasing them as substrates for an oxygenase side reaction of the enzyme. The structures also show that PS either stabilizes the thiamin diphosphate (ThDP)-peracetate adduct, a product of this oxygenase reaction, or traps within the active site an intact molecule of peracetate in the presence of a degraded form of ThDP: thiamine aminoethenethiol diphosphate. Kinetic analysis shows that PS inhibits AHAS by a combination of events involving FAD oxidation and chemical alteration of ThDP. With the emergence of increasing levels of resistance toward front-line herbicides and the need to optimize the use of arable land, these data suggest strategies for next generation herbicide design.
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4
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Lonhienne T, Garcia MD, Noble C, Harmer J, Fraser JA, Williams CM, Guddat LW. High Resolution Crystal Structures of the Acetohydroxyacid Synthase‐Pyruvate Complex Provide New Insights into Its Catalytic Mechanism. ChemistrySelect 2017. [DOI: 10.1002/slct.201702128] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Thierry Lonhienne
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Mario D. Garcia
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Chris Noble
- Centre for Advanced Imaging The University of Queensland Brisbane 4072 QLD Australia
| | - Jeffrey Harmer
- Centre for Advanced Imaging The University of Queensland Brisbane 4072 QLD Australia
| | - James A. Fraser
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Craig M. Williams
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Luke W. Guddat
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
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5
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Zhang J, Liu Y. Theoretical study of the catalytic mechanism of glyoxylate carboligase and its mutant V51E. Theor Chem Acc 2017. [DOI: 10.1007/s00214-017-2079-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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6
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The 2.0 Å X-ray structure for yeast acetohydroxyacid synthase provides new insights into its cofactor and quaternary structure requirements. PLoS One 2017; 12:e0171443. [PMID: 28178302 PMCID: PMC5298238 DOI: 10.1371/journal.pone.0171443] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Accepted: 01/20/2017] [Indexed: 11/19/2022] Open
Abstract
Acetohydroxyacid synthase (AHAS) catalyzes the first step of branched-chain amino acid biosynthesis, a pathway essential to the life-cycle of plants and micro-organisms. The catalytic subunit has thiamin diphosphate (ThDP) and flavin adenine dinucleotide (FAD) as indispensable co-factors. A new, high resolution, 2.0 Å crystal structure of Saccharomyces cerevisiae AHAS reveals that the dimer is asymmetric, with the catalytic centres having distinct structures where FAD is trapped in two different conformations indicative of different redox states. Two molecules of oxygen (O2) are bound on the surface of each active site and a tunnel in the polypeptide appears to passage O2 to the active site independently of the substrate. Thus, O2 appears to play a novel “co-factor” role in this enzyme. We discuss the functional implications of these features of the enzyme that have not previously been described.
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7
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Lonhienne T, Garcia MD, Guddat LW. The Role of a FAD Cofactor in the Regulation of Acetohydroxyacid Synthase by Redox Signaling Molecules. J Biol Chem 2017; 292:5101-5109. [PMID: 28159840 DOI: 10.1074/jbc.m116.773242] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Revised: 01/25/2017] [Indexed: 11/06/2022] Open
Abstract
Acetohydroxyacid synthase (AHAS) catalyzes the first step of branched-chain amino acid (BCAA) biosynthesis, a pathway essential to the lifecycle of plants and microorganisms. This enzyme is of high interest because its inhibition is at the base of the exceptional potency of herbicides and potentially a target for the discovery of new antimicrobial drugs. The enzyme has conserved attributes from its predicted ancestor, pyruvate oxidase, such as a ubiquinone-binding site and the requirement for FAD as cofactor. Here, we show that these requirements are linked to the regulation of AHAS, in relationship to its anabolic function. Using various soluble quinone derivatives (e.g. ubiquinones), we reveal a new path of down-regulation of AHAS activity involving inhibition by oxidized redox-signaling molecules. The inhibition process relies on two factors specific to AHAS: (i) the requirement of a reduced FAD cofactor for the enzyme to be active and (ii) a characteristic slow rate of FAD reduction by the pyruvate oxidase side reaction of the enzyme. The mechanism of inhibition involves the oxidation of the FAD cofactor, leading to a time-dependent inhibition of AHAS correlated with the slow process of FAD re-reduction. The existence and conservation of such a complex mechanism suggests that the redox level of the environment regulates the BCAA biosynthesis pathway. This mode of regulation appears to be the foundation of the inhibitory activity of many of the commercial herbicides that target AHAS.
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Affiliation(s)
- Thierry Lonhienne
- From the School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, 4072 Queensland, Australia
| | - Mario D Garcia
- From the School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, 4072 Queensland, Australia
| | - Luke W Guddat
- From the School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, 4072 Queensland, Australia
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8
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Liu Y, Li Y, Wang X. Acetohydroxyacid synthases: evolution, structure, and function. Appl Microbiol Biotechnol 2016; 100:8633-49. [DOI: 10.1007/s00253-016-7809-9] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Revised: 07/28/2016] [Accepted: 08/12/2016] [Indexed: 10/21/2022]
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9
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Lonhienne T, Nouwens A, Williams CM, Fraser JA, Lee Y, West NP, Guddat LW. Commercial Herbicides Can Trigger the Oxidative Inactivation of Acetohydroxyacid Synthase. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201511985] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Thierry Lonhienne
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Amanda Nouwens
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Craig M. Williams
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - James A. Fraser
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Yu‐Ting Lee
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Nicholas P. West
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Luke W. Guddat
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
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10
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Lonhienne T, Nouwens A, Williams CM, Fraser JA, Lee Y, West NP, Guddat LW. Commercial Herbicides Can Trigger the Oxidative Inactivation of Acetohydroxyacid Synthase. Angew Chem Int Ed Engl 2016; 55:4247-51. [DOI: 10.1002/anie.201511985] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2015] [Revised: 01/22/2016] [Indexed: 11/10/2022]
Affiliation(s)
- Thierry Lonhienne
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Amanda Nouwens
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Craig M. Williams
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - James A. Fraser
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Yu‐Ting Lee
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Nicholas P. West
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
| | - Luke W. Guddat
- School of Chemistry and Molecular Biosciences The University of Queensland Brisbane 4072 QLD Australia
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11
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Eram MS, Sarafuddin B, Gong F, Ma K. Characterization of acetohydroxyacid synthase from the hyperthermophilic bacterium Thermotoga maritima. Biochem Biophys Rep 2015; 4:89-97. [PMID: 29124191 PMCID: PMC5668897 DOI: 10.1016/j.bbrep.2015.08.014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Revised: 08/24/2015] [Accepted: 08/24/2015] [Indexed: 11/30/2022] Open
Abstract
Acetohydroxyacid synthase (AHAS) is the key enzyme in branched chain amino acid biosynthesis pathway. The enzyme activity and properties of a highly thermostable AHAS from the hyperthermophilic bacterium Thermotoga maritima is being reported. The catalytic and regulatory subunits of AHAS from T. maritima were over-expressed in Escherichia coli. The recombinant subunits were purified using a simplified procedure including a heat-treatment step followed by chromatography. A discontinuous colorimetric assay method was optimized and used to determine the kinetic parameters. AHAS activity was determined to be present in several Thermotogales including T. maritima. The catalytic subunit of T. maritima AHAS was purified approximately 30-fold, with an AHAS activity of approximately 160±27 U/mg and native molecular mass of 156±6 kDa. The regulatory subunit was purified to homogeneity and showed no catalytic activity as expected. The optimum pH and temperature for AHAS activity were 7.0 and 85 °C, respectively. The apparent Km and Vmax for pyruvate were 16.4±2 mM and 246±7 U/mg, respectively. Reconstitution of the catalytic and regulatory subunits led to increased AHAS activity. This is the first report on characterization of an isoleucine, leucine, and valine operon (ilv operon) enzyme from a hyperthermophilic microorganism and may contribute to our understanding of the physiological pathways in Thermotogales. The enzyme represents the most active and thermostable AHAS reported so far. First report of AHAS from a hyperthermophilic bacterium. Catalytic and regulatory subunits of AHAS of T. maritima was expressed in E. coli. Recombinant proteins were purified using a simplified procedure. Enzyme represents the most active and thermostable AHAS reported so far. Kinetic parameters were determined for the purified recombinant enzyme
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Key Words
- AHAS, acetohydroxyacid synthase
- Acetohydroxyacid synthase
- BCAA, branched chain amino acid
- Branched-chain amino acids
- CCE, crude cell extract
- CFE, cell-free extract
- HTCCE, heat-treated crude cell extract
- Hyperthermophiles
- IB, inclusion body
- IMAC, immobilized metal affinity chromatography
- TPP, thiamine pyrophosphate
- Thermotogales
- TmAHAS, Thermotoga maritima acetohydroxyacid synthase
- ilv, isoleucine, leucine, valine
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Affiliation(s)
- Mohammad S Eram
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
| | - Benozir Sarafuddin
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
| | - Frank Gong
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
| | - Kesen Ma
- Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
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Characterization and modification of enzymes in the 2-ketoisovalerate biosynthesis pathway of Ralstonia eutropha H16. Appl Microbiol Biotechnol 2014; 99:761-74. [DOI: 10.1007/s00253-014-5965-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Revised: 07/15/2014] [Accepted: 07/16/2014] [Indexed: 11/27/2022]
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13
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Belenky I, Steinmetz A, Vyazmensky M, Barak Z, Tittmann K, Chipman DM. Many of the functional differences between acetohydroxyacid synthase (AHAS) isozyme I and other AHASs are a result of the rapid formation and breakdown of the covalent acetolactate-thiamin diphosphate adduct in AHAS I. FEBS J 2012; 279:1967-79. [DOI: 10.1111/j.1742-4658.2012.08577.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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14
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Steinbach A, Fraas S, Harder J, Warkentin E, Kroneck PMH, Ermler U. Crystal structure of a ring-cleaving cyclohexane-1,2-dione hydrolase, a novel member of the thiamine diphosphate enzyme family. FEBS J 2012; 279:1209-19. [DOI: 10.1111/j.1742-4658.2012.08513.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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15
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Balakrishnan A, Gao Y, Moorjani P, Nemeria NS, Tittmann K, Jordan F. Bifunctionality of the thiamin diphosphate cofactor: assignment of tautomeric/ionization states of the 4'-aminopyrimidine ring when various intermediates occupy the active sites during the catalysis of yeast pyruvate decarboxylase. J Am Chem Soc 2012; 134:3873-85. [PMID: 22300533 PMCID: PMC3295232 DOI: 10.1021/ja211139c] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Thiamin diphosphate (ThDP) dependent enzymes perform crucial C-C bond forming and breaking reactions in sugar and amino acid metabolism and in biosynthetic pathways via a sequence of ThDP-bound covalent intermediates. A member of this superfamily, yeast pyruvate decarboxylase (YPDC) carries out the nonoxidative decarboxylation of pyruvate and is mechanistically a simpler ThDP enzyme. YPDC variants created by substitution at the active center (D28A, E51X, and E477Q) and on the substrate activation pathway (E91D and C221E) display varying activity, suggesting that they stabilize different covalent intermediates. To test the role of both rings of ThDP in YPDC catalysis (the 4'-aminopyrimidine as acid-base, and thiazolium as electrophilic covalent catalyst), we applied a combination of steady state and time-resolved circular dichroism experiments (assessing the state of ionization and tautomerization of enzyme-bound ThDP-related intermediates), and chemical quench of enzymatic reaction mixtures followed by NMR characterization of the ThDP-bound intermediates released from YPDC (assessing occupancy of active centers by these intermediates and rate-limiting steps). Results suggest the following: (1) Pyruvate and analogs induce active site asymmetry in YPDC and variants. (2) The rare 1',4'-iminopyrimidine ThDP tautomer participates in formation of ThDP-bound intermediates. (3) Propionylphosphinate also binds at the regulatory site and its binding is reflected by catalytic events at the active site 20 Å away. (4) YPDC stabilizes an electrostatic model for the 4'-aminopyrimidinium ionization state, an important contribution of the protein to catalysis. The combination of tools used provides time-resolved details about individual events during ThDP catalysis; the methods are transferable to other ThDP superfamily members.
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Affiliation(s)
| | - Yuhong Gao
- Department of Chemistry, Rutgers University, Newark, NJ 07102, USA
| | - Prerna Moorjani
- Department of Chemistry, Rutgers University, Newark, NJ 07102, USA
| | | | - Kai Tittmann
- Albrecht-von-Haller Institute & Göttingen Center for Molecular Biosciences, Georg-August University Göttingen, D-37077 Göttingen, Germany
| | - Frank Jordan
- Department of Chemistry, Rutgers University, Newark, NJ 07102, USA
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Gedi V, Yoon MY. Bacterial acetohydroxyacid synthase and its inhibitors - a summary of their structure, biological activity and current status. FEBS J 2012; 279:946-63. [DOI: 10.1111/j.1742-4658.2012.08505.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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17
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Cyclohexane-1,2-dione hydrolase from denitrifying Azoarcus sp. strain 22Lin, a novel member of the thiamine diphosphate enzyme family. J Bacteriol 2011; 193:6760-9. [PMID: 21965568 DOI: 10.1128/jb.05348-11] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Alicyclic compounds with hydroxyl groups represent common structures in numerous natural compounds, such as terpenes and steroids. Their degradation by microorganisms in the absence of dioxygen may involve a C-C bond ring cleavage to form an aliphatic intermediate that can be further oxidized. The cyclohexane-1,2-dione hydrolase (CDH) (EC 3.7.1.11) from denitrifying Azoarcus sp. strain 22Lin, grown on cyclohexane-1,2-diol as a sole electron donor and carbon source, is the first thiamine diphosphate (ThDP)-dependent enzyme characterized to date that cleaves a cyclic aliphatic compound. The degradation of cyclohexane-1,2-dione (CDO) to 6-oxohexanoate comprises the cleavage of a C-C bond adjacent to a carbonyl group, a typical feature of reactions catalyzed by ThDP-dependent enzymes. In the subsequent NAD(+)-dependent reaction, 6-oxohexanoate is oxidized to adipate. CDH has been purified to homogeneity by the criteria of gel electrophoresis (a single band at ∼59 kDa; calculated molecular mass, 64.5 kDa); in solution, the enzyme is a homodimer (∼105 kDa; gel filtration). As isolated, CDH contains 0.8 ± 0.05 ThDP, 1.0 ± 0.02 Mg(2+), and 1.0 ± 0.015 flavin adenine dinucleotide (FAD) per monomer as a second organic cofactor, the role of which remains unclear. Strong reductants, Ti(III)-citrate, Na(+)-dithionite, and the photochemical 5-deazaflavin/oxalate system, led to a partial reduction of the FAD chromophore. The cleavage product of CDO, 6-oxohexanoate, was also a substrate; the corresponding cyclic 1,3- and 1,4-diones did not react with CDH, nor did the cis- and trans-cyclohexane diols. The enzymes acetohydroxyacid synthase (AHAS) from Saccharomyces cerevisiae, pyruvate oxidase (POX) from Lactobacillus plantarum, benzoylformate decarboxylase from Pseudomonas putida, and pyruvate decarboxylase from Zymomonas mobilis were identified as the closest relatives of CDH by comparative amino acid sequence analysis, and a ThDP binding motif and a 2-fold Rossmann fold for FAD binding could be localized at the C-terminal end and central region of CDH, respectively. A first mechanism for the ring cleavage of CDO is presented, and it is suggested that the FAD cofactor in CDH is an evolutionary relict.
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Vyazmensky M, Steinmetz A, Meyer D, Golbik R, Barak Z, Tittmann K, Chipman DM. Significant Catalytic Roles for Glu47 and Gln 110 in All Four of the C−C Bond-Making and -Breaking Steps of the Reactions of Acetohydroxyacid Synthase II. Biochemistry 2011; 50:3250-60. [DOI: 10.1021/bi102051h] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Maria Vyazmensky
- Ben-Gurion University of the Negev, Department of Life Sciences, Beer-Sheva 84105, Israel
| | - Andrea Steinmetz
- Georg-August University Göttingen, Albrecht-von-Haller-Institute and Göttingen Centre for Molecular Biosciences, Ernst-Caspari-Haus, Department of Bioanalytics, Justus-von-Liebig Weg 11, 37077 Göttingen, Germany
- Martin-Luther University Halle-Wittenberg, Institute for Biochemistry and Biotechnology, Kurt-Mothes-Strasse 3, 06120 Halle/Saale, Germany
| | - Danilo Meyer
- Georg-August University Göttingen, Albrecht-von-Haller-Institute and Göttingen Centre for Molecular Biosciences, Ernst-Caspari-Haus, Department of Bioanalytics, Justus-von-Liebig Weg 11, 37077 Göttingen, Germany
- Martin-Luther University Halle-Wittenberg, Institute for Biochemistry and Biotechnology, Kurt-Mothes-Strasse 3, 06120 Halle/Saale, Germany
| | - Ralph Golbik
- Martin-Luther University Halle-Wittenberg, Institute for Biochemistry and Biotechnology, Kurt-Mothes-Strasse 3, 06120 Halle/Saale, Germany
| | - Ze'ev Barak
- Ben-Gurion University of the Negev, Department of Life Sciences, Beer-Sheva 84105, Israel
| | - Kai Tittmann
- Georg-August University Göttingen, Albrecht-von-Haller-Institute and Göttingen Centre for Molecular Biosciences, Ernst-Caspari-Haus, Department of Bioanalytics, Justus-von-Liebig Weg 11, 37077 Göttingen, Germany
- Martin-Luther University Halle-Wittenberg, Institute for Biochemistry and Biotechnology, Kurt-Mothes-Strasse 3, 06120 Halle/Saale, Germany
| | - David M. Chipman
- Ben-Gurion University of the Negev, Department of Life Sciences, Beer-Sheva 84105, Israel
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19
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Bunik VI, Schloss JV, Pinto JT, Dudareva N, Cooper AJL. A survey of oxidative paracatalytic reactions catalyzed by enzymes that generate carbanionic intermediates: implications for ROS production, cancer etiology, and neurodegenerative diseases. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2011; 77:307-60. [PMID: 21692372 DOI: 10.1002/9780470920541.ch7] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Victoria I Bunik
- School of Bioinformatics and Bioengineering, and Belozersky Institute of Physico-Chemical Biology, Moscow Lomonosov State University, Moscow, Russian Federation
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20
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Steinmetz A, Vyazmensky M, Meyer D, Barak Z, Golbik R, Chipman DM, Tittmann K. Valine 375 and Phenylalanine 109 Confer Affinity and Specificity for Pyruvate as Donor Substrate in Acetohydroxy Acid Synthase Isozyme II from Escherichia coli. Biochemistry 2010; 49:5188-99. [DOI: 10.1021/bi100555q] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Andrea Steinmetz
- Albrecht-von-Haller-Institute and Göttingen Centre for Molecular Biosciences, Ernst-Caspari-Haus, Department of Bioanalytics, Georg-August University Göttingen, Justus-von-Liebig Weg 11, 37077 Göttingen, Germany
| | - Maria Vyazmensky
- Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
| | - Danilo Meyer
- Albrecht-von-Haller-Institute and Göttingen Centre for Molecular Biosciences, Ernst-Caspari-Haus, Department of Bioanalytics, Georg-August University Göttingen, Justus-von-Liebig Weg 11, 37077 Göttingen, Germany
| | - Ze′ev Barak
- Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
| | - Ralph Golbik
- Institute for Biochemistry and Biotechnology, Martin-Luther University Halle-Wittenberg, Kurt-Mothes-Strasse 3, 06120 Halle/Saale, Germany
| | - David M. Chipman
- Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
| | - Kai Tittmann
- Albrecht-von-Haller-Institute and Göttingen Centre for Molecular Biosciences, Ernst-Caspari-Haus, Department of Bioanalytics, Georg-August University Göttingen, Justus-von-Liebig Weg 11, 37077 Göttingen, Germany
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Weidner A, Neumann P, Pech A, Stubbs MT, Tittmann K. New insights into the membrane-binding and activation mechanism of pyruvate oxidase from Escherichia coli. ACTA ACUST UNITED AC 2009. [DOI: 10.1016/j.molcatb.2009.02.020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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22
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23
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Wang JG, Lee PKM, Dong YH, Pang SS, Duggleby RG, Li ZM, Guddat LW. Crystal structures of two novel sulfonylurea herbicides in complex with Arabidopsis thaliana acetohydroxyacid synthase. FEBS J 2009; 276:1282-90. [DOI: 10.1111/j.1742-4658.2009.06863.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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24
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Structural basis for membrane binding and catalytic activation of the peripheral membrane enzyme pyruvate oxidase from Escherichia coli. Proc Natl Acad Sci U S A 2008; 105:17390-5. [PMID: 18988747 DOI: 10.1073/pnas.0805027105] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The thiamin- and flavin-dependent peripheral membrane enzyme pyruvate oxidase from E. coli catalyzes the oxidative decarboxylation of the central metabolite pyruvate to CO(2) and acetate. Concomitant reduction of the enzyme-bound flavin triggers membrane binding of the C terminus and shuttling of 2 electrons to ubiquinone 8, a membrane-bound mobile carrier of the electron transport chain. Binding to the membrane in vivo or limited proteolysis in vitro stimulate the catalytic proficiency by 2 orders of magnitude. The molecular mechanisms by which membrane binding and activation are governed have remained enigmatic. Here, we present the X-ray crystal structures of the full-length enzyme and a proteolytically activated truncation variant lacking the last 23 C-terminal residues inferred as important in membrane binding. In conjunction with spectroscopic results, the structural data pinpoint a conformational rearrangement upon activation that exposes the autoinhibitory C terminus, thereby freeing the active site. In the activated enzyme, Phe-465 swings into the active site and wires both cofactors for efficient electron transfer. The isolated C terminus, which has no intrinsic helix propensity, folds into a helical structure in the presence of micelles.
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25
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Kluger R, Tittmann K. Thiamin diphosphate catalysis: enzymic and nonenzymic covalent intermediates. Chem Rev 2008; 108:1797-833. [PMID: 18491870 DOI: 10.1021/cr068444m] [Citation(s) in RCA: 216] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ronald Kluger
- Davenport Laboratories, Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6 Canada.
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Duggleby RG, McCourt JA, Guddat LW. Structure and mechanism of inhibition of plant acetohydroxyacid synthase. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2008; 46:309-24. [PMID: 18234503 DOI: 10.1016/j.plaphy.2007.12.004] [Citation(s) in RCA: 188] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2007] [Indexed: 05/04/2023]
Abstract
Plants and microorganisms synthesize valine, leucine and isoleucine via a common pathway in which the first reaction is catalysed by acetohydroxyacid synthase (AHAS, EC 2.2.1.6). This enzyme is of substantial importance because it is the target of several herbicides, including all members of the popular sulfonylurea and imidazolinone families. However, the emergence of resistant weeds due to mutations that interfere with the inhibition of AHAS is now a worldwide problem. Here we summarize recent ideas on the way in which these herbicides inhibit the enzyme, based on the 3D structure of Arabidopsis thaliana AHAS. This structure also reveals important clues for understanding how various mutations can lead to herbicide resistance.
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Affiliation(s)
- Ronald G Duggleby
- RDBiotech, 22 Parklands Boulevard, Little Mountain, Queensland 4551, Australia.
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Choi KJ, Noh KM, Kim DE, Ha BH, Kim EE, Yoon MY. Identification of the catalytic subunit of acetohydroxyacid synthase in Haemophilus influenzae and its potent inhibitors. Arch Biochem Biophys 2007; 466:24-30. [PMID: 17718999 DOI: 10.1016/j.abb.2007.07.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2007] [Revised: 07/07/2007] [Accepted: 07/11/2007] [Indexed: 11/22/2022]
Abstract
Acetohydroxyacid synthase (AHAS; EC 2.2.1.6) is a thiamin diphosphate- (ThDP)- and FAD-dependent enzyme that catalyzes the first common step in the biosynthetic pathway of the branched-amino acids (BCAAs) leucine, isoleucine, and valine. The gene from Haemophilus influenzae that encodes the AHAS catalytic subunit was cloned, overexpressed in Escherichia coli BL21(DE3), and purified to homogeneity. The purified H. influenzae AHAS catalytic subunit (Hin-AHAS) appeared as a single band on SDS-PAGE gel, with a molecular mass of approximately 63 kDa. The enzyme catalyzes the condensation of two molecules of pyruvate to form acetolactate, with a K(m) of 9.2mM and the specific activity of 1.5 micromol/min/mg. The cofactor activation constant (K(c)=13.5 microM) and the dissociation constant (K(d)=3.3 microM) of ThDP were also determined by enzymatic assay and tryptophan fluorescence quenching studies, respectively. We screened a chemical library to discover new inhibitors of the Hin AHAS catalytic subunit. Through which, AVS-2087 (IC(50)=0.53 microM), KSW30191 (IC(50)=1.42 microM), and KHG20612 (IC(50)=4.91 microM) displayed potent inhibition as compare to sulfometuron methyl (IC(50)=276.31 microM).
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Affiliation(s)
- Kyoung-Jae Choi
- Department of Chemistry, Hanyang University, 17 Haedang-dong, Sungdong-gu, Seoul 133-791, Republic of Korea
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28
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McCourt JA, Duggleby RG. Acetohydroxyacid synthase and its role in the biosynthetic pathway for branched-chain amino acids. Amino Acids 2006; 31:173-210. [PMID: 16699828 DOI: 10.1007/s00726-005-0297-3] [Citation(s) in RCA: 171] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2005] [Accepted: 12/09/2005] [Indexed: 11/25/2022]
Abstract
The branched-chain amino acids are synthesized by plants, fungi and microorganisms, but not by animals. Therefore, the enzymes of this pathway are potential target sites for the development of antifungal agents, antimicrobials and herbicides. Most research has focused upon the first enzyme in this biosynthetic pathway, acetohydroxyacid synthase (AHAS) largely because it is the target site for many commercial herbicides. In this review we provide a brief overview of the important properties of each enzyme within the pathway and a detailed summary of the most recent AHAS research, against the perspective of work that has been carried out over the past 50 years.
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Affiliation(s)
- J A McCourt
- School of Molecular and Microbial Sciences, University of Queensland, Brisbane, Australia
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29
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Chipman DM, Duggleby RG, Tittmann K. Mechanisms of acetohydroxyacid synthases. Curr Opin Chem Biol 2006; 9:475-81. [PMID: 16055369 DOI: 10.1016/j.cbpa.2005.07.002] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2005] [Accepted: 07/18/2005] [Indexed: 11/17/2022]
Abstract
Acetohydroxyacid synthases are thiamin diphosphate- (ThDP-) dependent biosynthetic enzymes found in all autotrophic organisms. Over the past 4-5 years, their mechanisms have been clarified and illuminated by protein crystallography, engineered mutagenesis and detailed single-step kinetic analysis. Pairs of catalytic subunits form an intimate dimer containing two active sites, each of which lies across a dimer interface and involves both monomers. The ThDP adducts of pyruvate, acetaldehyde and the product acetohydroxyacids can be detected quantitatively after rapid quenching. Determination of the distribution of intermediates by NMR then makes it possible to calculate individual forward unimolecular rate constants. The enzyme is the target of several herbicides and structures of inhibitor-enzyme complexes explain the herbicide-enzyme interaction.
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Affiliation(s)
- David M Chipman
- Department of Life Sciences, Ben-Gurion University POB 653, Beer-Sheva 84105, Israel
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McCourt JA, Pang SS, King-Scott J, Guddat LW, Duggleby RG. Herbicide-binding sites revealed in the structure of plant acetohydroxyacid synthase. Proc Natl Acad Sci U S A 2006; 103:569-73. [PMID: 16407096 PMCID: PMC1334660 DOI: 10.1073/pnas.0508701103] [Citation(s) in RCA: 213] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The sulfonylureas and imidazolinones are potent commercial herbicide families. They are among the most popular choices for farmers worldwide, because they are nontoxic to animals and highly selective. These herbicides inhibit branched-chain amino acid biosynthesis in plants by targeting acetohydroxyacid synthase (AHAS, EC 2.2.1.6). This report describes the 3D structure of Arabidopsis thaliana AHAS in complex with five sulfonylureas (to 2.5 A resolution) and with the imidazolinone, imazaquin (IQ; 2.8 A). Neither class of molecule has a structure that mimics the substrates for the enzyme, but both inhibit by blocking a channel through which access to the active site is gained. The sulfonylureas approach within 5 A of the catalytic center, which is the C2 atom of the cofactor thiamin diphosphate, whereas IQ is at least 7 A from this atom. Ten of the amino acid residues that bind the sulfonylureas also bind IQ. Six additional residues interact only with the sulfonylureas, whereas there are two residues that bind IQ but not the sulfonylureas. Thus, the two classes of inhibitor occupy partially overlapping sites but adopt different modes of binding. The increasing emergence of resistant weeds due to the appearance of mutations that interfere with the inhibition of AHAS is now a worldwide problem. The structures described here provide a rational molecular basis for understanding these mutations, thus allowing more sophisticated AHAS inhibitors to be developed. There is no previously described structure for any plant protein in complex with a commercial herbicide.
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Affiliation(s)
- Jennifer A McCourt
- School of Molecular and Microbial Sciences, University of Queensland, Brisbane QLD 4072, Australia
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31
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Tittmann K, Wille G, Golbik R, Weidner A, Ghisla S, Hübner G. Radical phosphate transfer mechanism for the thiamin diphosphate- and FAD-dependent pyruvate oxidase from Lactobacillus plantarum. Kinetic coupling of intercofactor electron transfer with phosphate transfer to acetyl-thiamin diphosphate via a transient FAD semiquinone/hydroxyethyl-ThDP radical pair. Biochemistry 2006; 44:13291-303. [PMID: 16201755 DOI: 10.1021/bi051058z] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The thiamin diphosphate (ThDP)- and flavin adenine dinucleotide (FAD)-dependent pyruvate oxidase from Lactobacillus plantarum catalyses the conversion of pyruvate, inorganic phosphate, and oxygen to acetyl-phosphate, carbon dioxide, and hydrogen peroxide. Central to the catalytic sequence, two reducing equivalents are transferred from the resonant carbanion/enamine forms of alpha-hydroxyethyl-ThDP to the adjacent flavin cofactor over a distance of approximately 7 A, followed by the phosphorolysis of the thereby formed acetyl-ThDP. Pre-steady-state and steady-state kinetics using time-resolved spectroscopy and a 1H NMR-based intermediate analysis indicate that both processes are kinetically coupled. In the presence of phosphate, intercofactor electron-transfer (ET) proceeds with an apparent first-order rate constant of 78 s(-1) and is kinetically gated by the preceding formation of the tetrahedral substrate-ThDP adduct 2-lactyl-ThDP and its decarboxylation. No transient flavin radicals are detectable in the reductive half-reaction. In contrast, when phosphate is absent, ET occurs in two discrete steps with apparent rate constants of 81 and 3 s(-1) and transient formation of a flavin semiquinone/hydroxyethyl-ThDP radical pair. Temperature dependence analysis according to the Marcus theory identifies the second step, the slow radical decay to be a true ET reaction. The redox potentials of the FAD(ox)/FAD(sq) (E1 = -37 mV) and FAD(sq)/FAD(red) (E2 = -87 mV) redox couples in the absence and presence of phosphate are identical. Both the Marcus analysis and fluorescence resonance energy-transfer studies using the fluorescent N3'-pyridyl-ThDP indicate the same cofactor distance in the presence or absence of phosphate. We deduce that the exclusive 10(2)-10(3)-fold rate enhancement of the second ET step is rather due to the nucleophilic attack of phosphate on the kinetically stabilized hydroxyethyl-ThDP radical resulting in a low-potential anion radical adduct than phosphate in a docking site being part of a through-bonded ET pathway in a stepwise mechanism of ET and phosphorolysis. Thus, LpPOX would constitute the first example of a radical-based phosphorolysis mechanism in biochemistry.
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Affiliation(s)
- Kai Tittmann
- Institut für Biochemie, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Strasse 3, D-06120 Halle/Saale, Germany.
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32
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Clark DP, Cronan JE. Two-Carbon Compounds and Fatty Acids as Carbon Sources. EcoSal Plus 2005; 1. [PMID: 26443509 DOI: 10.1128/ecosalplus.3.4.4] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2004] [Indexed: 06/05/2023]
Abstract
This review concerns the uptake and degradation of those molecules that are wholly or largely converted to acetyl-coenzyme A (CoA) in the first stage of metabolism in Escherichia coli and Salmonella enterica. These include acetate, acetoacetate, butyrate and longer fatty acids in wild type cells plus ethanol and some longer alcohols in certain mutant strains. Entering metabolism as acetyl-CoA has two important general consequences. First, generation of energy from acetyl-CoA requires operation of both the citric acid cycle and the respiratory chain to oxidize the NADH produced. Hence, acetyl-CoA serves as an energy source only during aerobic growth or during anaerobic respiration with such alternative electron acceptors as nitrate or trimethylamine oxide. In the absence of a suitable oxidant, acetyl-CoA is converted to a mixture of acetic acid and ethanol by the pathways of anaerobic fermentation. Catabolism of acetyl-CoA via the citric acid cycle releases both carbon atoms of the acetyl moiety as carbon dioxide and growth on these substrates as sole carbon source therefore requires the operation of the glyoxylate bypass to generate cell material. The pair of related two-carbon compounds, glycolate and glyoxylate are also discussed. However, despite having two carbons, these are metabolized via malate and glycerate, not via acetyl-CoA. In addition, mutants of E. coli capable of growth on ethylene glycol metabolize it via the glycolate pathway, rather than via acetyl- CoA. Propionate metabolism is also discussed because in many respects its pathway is analogous to that of acetate. The transcriptional regulation of these pathways is discussed in detail.
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Affiliation(s)
- David P Clark
- Department of Microbiology, Southern Illinois University, Carbondale, Illinois 62901
| | - John E Cronan
- Departments of Microbiology and Biochemistry, University of Illinois, B103 CLSL, 601 S. Goodwin Avenue, Urbana, Illinois 61801
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33
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Jordan F, Nemeria NS. Experimental observation of thiamin diphosphate-bound intermediates on enzymes and mechanistic information derived from these observations. Bioorg Chem 2005; 33:190-215. [PMID: 15888311 PMCID: PMC4189838 DOI: 10.1016/j.bioorg.2005.02.001] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2004] [Revised: 02/08/2005] [Accepted: 02/10/2005] [Indexed: 11/27/2022]
Abstract
Thiamin diphosphate (ThDP), the vitamin B1 coenzyme, is an excellent representative of coenzymes, which carry out electrophilic catalysis by forming a covalent complex with their substrates. The function of ThDP is to greatly increase the acidity of two carbon acids by stabilizing their conjugate bases, the ylide/C2-carbanion of the thiazolium ring and the C2alpha-carbanion (or enamine) once the substrate binds to ThDP. In recent years, several ThDP-bound intermediates on such pathways have been characterized by both solution and solid-state (X-ray) methods. Prominent among these advances are X-ray crystallographic results identifying both oxidative and non-oxidative intermediates, rapid chemical quench followed by NMR detection of a several intermediates which are stable under acidic conditions, and circular dichroism detection of the 1',4'-imino tautomer of ThDP in some of the intermediates. Some of these methods also enable the investigator to determine the rate-limiting step in the complex series of steps.
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Affiliation(s)
- Frank Jordan
- Department of Chemistry, Rutgers University, Newark, NJ 07102, USA
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Le DT, Yoon MY, Tae Kim Y, Choi JD. Two consecutive aspartic acid residues conferring herbicide resistance in tobacco acetohydroxy acid synthase. BIOCHIMICA ET BIOPHYSICA ACTA 2005; 1749:103-12. [PMID: 15848141 DOI: 10.1016/j.bbapap.2005.02.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2004] [Revised: 02/22/2005] [Accepted: 02/24/2005] [Indexed: 10/25/2022]
Abstract
Acetohydroxy acid synthase (AHAS) catalyzes the first common step in the biosynthesis pathway of the branch chain amino acids in plants and microorganisms. A great deal of interest has been focused on AHAS since it was identified as the target of several classes of potent herbicides. In an effort to produce a mutant usable in the development of an herbicide-resistant transgenic plant, two consecutive aspartic acid residues, which are very likely positioned next to the enzyme-bound herbicide sulfonylurea as the homologous residues in AHAS from yeast, were selected for this study. Four single-point mutants and two double mutants were constructed, and designated D374A, D374E, D375A, D375E, D374A/D375A, and D374E/D375E. All mutants were active, but the D374A mutant exhibited substrate inhibition at high concentrations. The D374E mutant also evidenced a profound reduction with regard to catalytic efficiency. The mutation of D375A increased the K(m) value for pyruvate nearly 10-fold. In contrast, the D375E mutant reduced this value by more than 3-fold. The double mutants exhibited synergistic reduction in catalytic efficiencies. All mutants constructed in this study proved to be strongly resistant to the herbicide sulfonylurea Londax. The double mutants and the mutants with the D375 residue were also strongly cross-resistant to the herbicide triazolopyrimidine TP. However, only the D374A mutant proved to be strongly resistant to imidazolinone Cadre. The data presented here indicate that the two residues, D374 and D375, are located at a common binding site for the herbicides sulfonylurea and triazolopyrimidine. D375E may be a valuable mutant for the development of herbicide-resistant transgenic plants.
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Affiliation(s)
- Dung Tien Le
- School of Life Sciences, Chungbuk National University, Cheongju 361-763, South Korea
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McCourt JA, Pang SS, Guddat LW, Duggleby RG. Elucidating the specificity of binding of sulfonylurea herbicides to acetohydroxyacid synthase. Biochemistry 2005; 44:2330-8. [PMID: 15709745 DOI: 10.1021/bi047980a] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Acetohydroxyacid synthase (AHAS, EC 2.2.1.6) is the target for the sulfonylurea herbicides, which act as potent inhibitors of the enzyme. Chlorsulfuron (marketed as Glean) and sulfometuron methyl (marketed as Oust) are two commercially important members of this family of herbicides. Here we report crystal structures of yeast AHAS in complex with chlorsulfuron (at a resolution of 2.19 A), sulfometuron methyl (2.34 A), and two other sulfonylureas, metsulfuron methyl (2.29 A) and tribenuron methyl (2.58 A). The structures observed suggest why these inhibitors have different potencies and provide clues about the differential effects of mutations in the active site tunnel on various inhibitors. In all of the structures, the thiamin diphosphate cofactor is fragmented, possibly as the result of inhibitor binding. In addition to thiamin diphosphate, AHAS requires FAD for activity. Recently, it has been reported that reduction of FAD can occur as a minor side reaction due to reaction with the carbanion/enamine of the hydroxyethyl-ThDP intermediate that is formed midway through the catalytic cycle. Here we report that the isoalloxazine ring has a bent conformation that would account for its ability to accept electrons from the hydroxyethyl intermediate. Most sequence and mutation data suggest that yeast AHAS is a high-quality model for the plant enzyme.
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Affiliation(s)
- Jennifer A McCourt
- Department of Biochemistry and Molecular Biology, The University of Queensland, Brisbane, Queensland 4072, Australia
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Nemeria N, Tittmann K, Joseph E, Zhou L, Vazquez-Coll MB, Arjunan P, Hübner G, Furey W, Jordan F. Glutamate 636 of the Escherichia coli pyruvate dehydrogenase-E1 participates in active center communication and behaves as an engineered acetolactate synthase with unusual stereoselectivity. J Biol Chem 2005; 280:21473-82. [PMID: 15802265 DOI: 10.1074/jbc.m502691200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The residue Glu636 is located near the thiamine diphosphate (ThDP) binding site of the Escherichia coli pyruvate dehydrogenase complex E1 subunit (PDHc-E1), and to probe its function two variants, E636A and E636Q were created with specific activities of 2.5 and 26% compared with parental PDHc-E1. According to both fluorescence binding and kinetic assays, the E636A variant behaved according to half-of-the-sites mechanism with respect to ThDP. In contrast, with the E636Q variant a K(d,ThDP) = 4.34 microM and K(m,ThDP) = 11 microM were obtained with behavior more reminiscent of the parental enzyme. The CD spectra of both variants gave evidence for formation of the 1',4'-iminopyrimidine tautomer on binding of phosphonolactylthiamine diphosphate, a stable analog of the substrate-ThDP covalent complex. Rapid formation of optically active (R)-acetolactate by both variants, but not by the parental enzyme, was observed by CD and NMR spectroscopy. The acetolactate configuration produced by the Glu636 variants is opposite that produced by the enzyme acetolactate synthase and the Asp28-substituted variants of yeast pyruvate decarboxylase, suggesting that the active centers of the two sets of enzymes exhibit different facial selectivity (re or si) vis à vis pyruvate. The tryptic peptide map (mass spectral analysis) revealed that the Glu636 substitution changed the mobility of a loop comprising amino acid residues from the ThDP binding fold. Apparently, the residue Glu636 has important functions both in active center communication and in protecting the active center from undesirable "carboligase" side reactions.
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Affiliation(s)
- Natalia Nemeria
- Department of Chemistry, Rutgers University, Newark, New Jersey 07102, USA.
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Tittmann K, Vyazmensky M, Hübner G, Barak Z, Chipman DM. The carboligation reaction of acetohydroxyacid synthase II: steady-state intermediate distributions in wild type and mutants by NMR. Proc Natl Acad Sci U S A 2005; 102:553-8. [PMID: 15640355 PMCID: PMC545553 DOI: 10.1073/pnas.0408210101] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The thiamin diphosphate (ThDP)-dependent enzyme acetohydroxyacid synthase (AHAS) catalyzes the first common step in branched-chain amino acid biosynthesis. By specific ligation of pyruvate with the alternative acceptor substrates 2-ketobutyrate and pyruvate, AHAS controls the flux through this branch point and determines the relative rates of synthesis of isoleucine, valine, and leucine, respectively. We used detailed NMR analysis to determine microscopic rate constants for elementary steps in the reactions of AHAS II and mutants altered at conserved residues Arg-276, Trp-464, and Met-250. In Arg276Lys, both the condensation of the enzyme-bound hydroxyethyl-ThDP carbanion/enamine (HEThDP) with the acceptor substrates and acetohydroxyacid release are slowed several orders of magnitude relative to the wild-type enzyme. We propose that the interaction of the guanidinium moiety of Arg-264 with the carboxylate of the acceptor ketoacid provides an optimal alignment of substrate and HEThDP orbitals in the reaction trajectory for acceptor ligation, whereas its interaction with the carboxylate of the covalent HEThDP-acceptor adduct plays a similar role in product release. Both Trp-464 and Met-250 affect the acceptor specificity. The high preference for ketobutyrate in the wild-type enzyme is lost in Trp464Leu as a consequence of similar forward rate constants of carboligation and product release for the alternative acceptors. In Met250Ala, the turnover rate is determined by the condensation of HEThDP with pyruvate and release of the acetolactate product, whereas the parallel steps with 2-ketobutyrate are considerably faster. We speculate that the specificity of carboligation and product liberation may be cumulative if the former is not completely committed.
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Affiliation(s)
- Kai Tittmann
- Department of Life Sciences, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel
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