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Zhao T, Li Y, Yuan S, Ye Y, Peng Z, Zhou R, Liu J. Structure-Based Design of Acetolactate Synthase From Bacillus licheniformis Improved Protein Stability Under Acidic Conditions. Front Microbiol 2020; 11:582909. [PMID: 33193222 PMCID: PMC7652814 DOI: 10.3389/fmicb.2020.582909] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Accepted: 10/06/2020] [Indexed: 11/13/2022] Open
Abstract
Catabolic acetolactate synthase (cALS) plays a crucial role in the quality of liquor because of its ability to catalyze the synthesis of the endogenous precursor product α-acetolactate of the aromatic compound tetramethylpyrazine (TTMP) and acetoin. However, the vulnerability of cALS to acidic conditions limits its application in the Chinese liquor brewing industry. Here we report the biochemical characterization of cALS from B. licheniformis T2 (BlALS) that was screened from Chinese liquor brewing microorganisms. BlALS showed optimal activity levels at pH 7.0, and the values of Km and Vmax were 27.26 mM and 6.9 mM⋅min–1, respectively. Through site-directed mutagenesis, we improved the stability of BlALS under acidic conditions. Replacing the two basic residues of BlALS with acidic mutations (N210D and H399D) significantly improved the acid tolerance of the enzyme with a prolonged half-life of 2.2 h (compared with wild-type BlALS of 0.8 h) at pH 4.0. Based on the analysis of homologous modeling, the positive charge area of the electrostatic potential on the protein surface and the number of hydrogen bonds near the active site increased, which helped BlALSN210D–H399D to withstand the acidic environment; this could extend its application in the food fermentation industry.
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Affiliation(s)
- Ting Zhao
- Faculty of Bioengineering, Wuliangye Liquor College, Sichuan University of Science and Engineering, Yibin, China
| | - Yuan Li
- Faculty of Bioengineering, Wuliangye Liquor College, Sichuan University of Science and Engineering, Yibin, China
| | - Siqi Yuan
- Faculty of Bioengineering, Wuliangye Liquor College, Sichuan University of Science and Engineering, Yibin, China
| | - Yang Ye
- Faculty of Bioengineering, Wuliangye Liquor College, Sichuan University of Science and Engineering, Yibin, China
| | | | - Rongqing Zhou
- College of Biomass Science and Engineering, Sichuan University, Chengdu, China
| | - Jun Liu
- Faculty of Bioengineering, Wuliangye Liquor College, Sichuan University of Science and Engineering, Yibin, China.,Wuliangye Group Co. Ltd., Yibin, China.,College of Biomass Science and Engineering, Sichuan University, Chengdu, China
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2
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Pelicaen R, Gonze D, Teusink B, De Vuyst L, Weckx S. Genome-Scale Metabolic Reconstruction of Acetobacter pasteurianus 386B, a Candidate Functional Starter Culture for Cocoa Bean Fermentation. Front Microbiol 2019; 10:2801. [PMID: 31921009 PMCID: PMC6915089 DOI: 10.3389/fmicb.2019.02801] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Accepted: 11/18/2019] [Indexed: 01/17/2023] Open
Abstract
Acetobacter pasteurianus 386B is a candidate functional starter culture for the cocoa bean fermentation process. To allow in silico simulations of its related metabolism in response to different environmental conditions, a genome-scale metabolic model for A. pasteurianus 386B was reconstructed. This is the first genome-scale metabolic model reconstruction for a member of the genus Acetobacter. The metabolic network reconstruction process was based on extensive genome re-annotation and comparative genomics analyses. The information content related to the functional annotation of metabolic enzymes and transporters was placed in a metabolic context by exploring and curating a Pathway/Genome Database of A. pasteurianus 386B using the Pathway Tools software. Metabolic reactions and curated gene-protein-reaction associations were bundled into a genome-scale metabolic model of A. pasteurianus 386B, named iAp386B454, containing 454 genes, 322 reactions, and 296 metabolites embedded in two cellular compartments. The reconstructed model was validated by performing growth experiments in a defined medium, which revealed that lactic acid as the sole carbon source could sustain growth of this strain. Further, the reconstruction of the A. pasteurianus 386B genome-scale metabolic model revealed knowledge gaps concerning the metabolism of this strain, especially related to the biosynthesis of its cell envelope and the presence or absence of metabolite transporters.
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Affiliation(s)
- Rudy Pelicaen
- Research Group of Industrial Microbiology and Food Biotechnology (IMDO), Faculty of Sciences and Bioengineering Sciences, Vrije Universiteit Brussel (VUB), Brussels, Belgium
- (IB) - Interuniversity Institute of Bioinformatics in Brussels (ULB-VUB), Brussels, Belgium
| | - Didier Gonze
- (IB) - Interuniversity Institute of Bioinformatics in Brussels (ULB-VUB), Brussels, Belgium
- Unité de Chronobiologie Théorique, Service de Chimie Physique, Faculté des Sciences, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - Bas Teusink
- Systems Bioinformatics, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
| | - Luc De Vuyst
- Research Group of Industrial Microbiology and Food Biotechnology (IMDO), Faculty of Sciences and Bioengineering Sciences, Vrije Universiteit Brussel (VUB), Brussels, Belgium
| | - Stefan Weckx
- Research Group of Industrial Microbiology and Food Biotechnology (IMDO), Faculty of Sciences and Bioengineering Sciences, Vrije Universiteit Brussel (VUB), Brussels, Belgium
- (IB) - Interuniversity Institute of Bioinformatics in Brussels (ULB-VUB), Brussels, Belgium
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Huo Y, Zhan Y, Wang Q, Li S, Yang S, Nomura CT, Wang C, Chen S. Acetolactate synthase (AlsS) in Bacillus licheniformis WX-02: enzymatic properties and efficient functions for acetoin/butanediol and L-valine biosynthesis. Bioprocess Biosyst Eng 2017; 41:87-96. [PMID: 29026998 DOI: 10.1007/s00449-017-1847-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Accepted: 09/23/2017] [Indexed: 11/25/2022]
Abstract
Acetolactate synthase catalyzes two molecules of pyruvates to form α-acetolactate, which is further converted to acetoin and 2,3-butanediol. In this study, by heterologous expression in Escherichia coli, the enzymatic properties of acetolactate synthase (AlsS) from Bacillus licheniformis WX-02 were characterized. Its K m and k cat for pyruvate were 3.96 mM and 514/s, respectively. It has the optimal activity at pH 6.5, 37 °C and was feedback inhibited by L-valine, L-leucine and L-isoleucine. Furthermore, the alsS-deficient strain could not produce acetoin, 2,3-butanediol, and L-valine, while the complementary strain was able to restore these capacities. The alsS overexpressing strain produced higher amounts of acetoin/2,3-butanediol (57.06 g/L) and L-valine (2.68 mM), which were 10.90 and 92.80% higher than those of the control strain, respectively. This is the first report regarding the in-depth understanding of AlsS enzymatic properties and its functions in B. licheniformis, and overexpression of AlsS can effectively improve acetoin/2,3-butanediol and L-valine production in B. licheniformis. We envision that this AlsS can also be applied in the improvement of acetoin/2,3-butanediol and L-valine production in other microbes.
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Affiliation(s)
- Yanli Huo
- School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, 730070, People's Republic of China
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, 430070, People's Republic of China
| | - Yangyang Zhan
- Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Environmental Microbial Technology Center of Hubei Province, College of Life Sciences, Hubei University, Wuhan, 430062, People's Republic of China
| | - Qin Wang
- Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Environmental Microbial Technology Center of Hubei Province, College of Life Sciences, Hubei University, Wuhan, 430062, People's Republic of China
| | - Shunyi Li
- Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Environmental Microbial Technology Center of Hubei Province, College of Life Sciences, Hubei University, Wuhan, 430062, People's Republic of China
| | - Shihui Yang
- Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Environmental Microbial Technology Center of Hubei Province, College of Life Sciences, Hubei University, Wuhan, 430062, People's Republic of China
| | - Christopher T Nomura
- Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Environmental Microbial Technology Center of Hubei Province, College of Life Sciences, Hubei University, Wuhan, 430062, People's Republic of China
- Department of Chemistry, The State University of New York College of Environmental Science and Forestry (SUNY ESF), Syracuse, NY, 13210, USA
| | - Changjun Wang
- Tobacco Research Institute of Hubei Province, Wuhan, 430062, People's Republic of China.
| | - Shouwen Chen
- Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Environmental Microbial Technology Center of Hubei Province, College of Life Sciences, Hubei University, Wuhan, 430062, People's Republic of China.
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, 430070, People's Republic of China.
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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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Lee SC, Jung IP, Baig IA, Chien PN, La IJ, Yoon MY. Mutational analysis of critical residues of FAD-independent catabolic acetolactate synthase from Enterococcus faecalis V583. Int J Biol Macromol 2014; 72:104-9. [PMID: 25128823 DOI: 10.1016/j.ijbiomac.2014.08.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2014] [Revised: 08/02/2014] [Accepted: 08/04/2014] [Indexed: 10/24/2022]
Abstract
Catabolic acetolactate synthase (cALS) from Enterococcus faecalis is a FAD-independent enzyme, which catalyzes the condensation of two molecules of pyruvate to produce acetolactate. Mutational and kinetic analyses of variants suggested the importance of H111, Q112, and Q411 residues for catalysis in cALS. The wild-type and variants were expressed as equally soluble proteins and co-migrated to a size of 60 kDa on SDS-PAGE. Importantly, H111 in cALS, which is widely present as phenylalanine in many other ThDP-dependent enzymes, plays a crucial role in substrate binding. Interestingly, the H111 variants, H111R and H111F, demonstrated altered specific activity of H111 variants with 17- and 26-fold increases in Km, respectively, compared to wild-type cALS. Furthermore, Q112 variants, Q112E, Q112N, and Q112V, exhibited significantly lower specific activity with 70-, 15-, and 10-fold higher Ks for ThDP, respectively. In the case of Q411, the variant Q411E showed a 10-fold rise in Km and a 20-fold increase in Ks for ThDP. Further, the molecular docking results indicated that the binding mode of ThDP was slightly affected in the variants of cALS. Based on these results, we suggest that H111 plays a role in substrate binding, and further suggest that Q112 and Q411 might be involved in ThDP binding of cALS.
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Affiliation(s)
- Sang-Choon Lee
- Department of Chemistry, College of Natural Science, Hanyang University, Seoul 133-791, Republic of Korea
| | - In-Pil Jung
- Department of Chemistry, College of Natural Science, Hanyang University, Seoul 133-791, Republic of Korea
| | - Irshad Ahmed Baig
- Department of Chemistry, College of Natural Science, Hanyang University, Seoul 133-791, Republic of Korea
| | - Pham Ngoc Chien
- Department of Chemistry, College of Natural Science, Hanyang University, Seoul 133-791, Republic of Korea
| | - Im-Joung La
- Department of Chemistry, College of Natural Science, Hanyang University, Seoul 133-791, Republic of Korea
| | - Moon-Young Yoon
- Department of Chemistry, College of Natural Science, Hanyang University, Seoul 133-791, Republic of Korea.
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Lee MY, Lee SC, Cho JH, Ryu SE, Koo BS, Yoon MY. Role of a Highly Conserved and Catalytically Important Glutamate-49 in the Enterococcus faecalis Acetolactate Synthase. B KOREAN CHEM SOC 2013. [DOI: 10.5012/bkcs.2013.34.2.669] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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7
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Characterization of recombinant FAD-independent catabolic acetolactate synthase from Enterococcus faecalis V583. Enzyme Microb Technol 2012. [PMID: 23199739 DOI: 10.1016/j.enzmictec.2012.10.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The catabolic acetolactate synthase (cALS) of Enterococcus faecalis V583 was cloned, expressed in Escherichia coli, and purified to homogeneity. The purified protein had a molecular weight of 60 kDa. The cALS of E. faecalis is highly homologous with other cALSs, while sharing low homology with its anabolic counterparts. The cALS of E. faecalis exhibits optimum activity at a temperature of 37°C and pH 6.8. Based on the enzyme characterization, the apparent K(m) for pyruvate was calculated to be 1.37 mM, while the K(c) for thiamin diphosphate (ThDP) and Mg(2+) were found to be 0.031 μM and 1.27 mM, respectively. Negligible absorbance at 450 nm and lack of activity enhancement upon addition of flavin adenine dinucleotide (FAD) to the assay buffer suggest that the cALS of E. faecalis is not FAD-dependent. The enzyme showed extreme stability against the organic solvent dimethyl sulfoxide (DMSO), whereas the activity decreased to less than 50% in the presence of acetone and ethanol.
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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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Pang SS, Duggleby RG, Schowen RL, Guddat LW. The crystal structures of Klebsiella pneumoniae acetolactate synthase with enzyme-bound cofactor and with an unusual intermediate. J Biol Chem 2003; 279:2242-53. [PMID: 14557277 DOI: 10.1074/jbc.m304038200] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Acetohydroxyacid synthase (AHAS) and acetolactate synthase (ALS) are thiamine diphosphate (ThDP)-dependent enzymes that catalyze the decarboxylation of pyruvate to give a cofactor-bound hydroxyethyl group, which is transferred to a second molecule of pyruvate to give 2-acetolactate. AHAS is found in plants, fungi, and bacteria, is involved in the biosynthesis of the branched-chain amino acids, and contains non-catalytic FAD. ALS is found only in some bacteria, is a catabolic enzyme required for the butanediol fermentation, and does not contain FAD. Here we report the 2.3-A crystal structure of Klebsiella pneumoniae ALS. The overall structure is similar to AHAS except for a groove that accommodates FAD in AHAS, which is filled with amino acid side chains in ALS. The ThDP cofactor has an unusual conformation that is unprecedented among the 26 known three-dimensional structures of nine ThDP-dependent enzymes, including AHAS. This conformation suggests a novel mechanism for ALS. A second structure, at 2.0 A, is described in which the enzyme is trapped halfway through the catalytic cycle so that it contains the hydroxyethyl intermediate bound to ThDP. The cofactor has a tricyclic structure that has not been observed previously in any ThDP-dependent enzyme, although similar structures are well known for free thiamine. This structure is consistent with our proposed mechanism and probably results from an intramolecular proton transfer within a tricyclic carbanion that is the true reaction intermediate. Modeling of the second molecule of pyruvate into the active site of the enzyme with the bound intermediate is consistent with the stereochemistry and specificity of ALS.
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Affiliation(s)
- Siew Siew Pang
- Department of Biochemistry and Molecular Biology, the University of Queensland, Brisbane, Queensland 4072, Australia
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Maestri O, Joset F. Regulation by external pH and stationary growth phase of the acetolactate synthase from Synechocystis PCC6803. Mol Microbiol 2000; 37:828-38. [PMID: 10972805 DOI: 10.1046/j.1365-2958.2000.02048.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Several characteristics identify the protein encoded by the alsS gene [sll1981 in Cyanobase (http://www.kazusa.or.jp/cyano/cyano. html)] of Synechocystis PCC6803 as an acetolactate synthase. The AlsS protein is about 60% homologous to the AlsS from Bacillus subtilis or other bacteria. These enzymes condense two pyruvates to form acetolactate, implicated in pH homeostasis via the acetoin-2, 3-butanediol pathway or in valine biosynthesis. Transcriptional fusions revealed that alsS was induced at the onset of stationary phase, as in B. subtilis, a situation leading to an increase in the pHout to above 11 in Synechocystis. This is the first cyanobacterial gene showing a dependence on pH for its expression. Induction was also obtained by the presence of > 100 mM Na+, the effect being prevented by amiloride, in agreement with Na+/H+ exchange in the pH homeostasis process. Homology of the Synechocystis AlsS protein to the close family of acetohydroxy acid synthases (including one in Synechocystis) is around 30%. These enzymes are involved in the parallel routes for valine/leucine and isoleucine biosynthesis. No phenotype of auxotrophy for any of these amino acids was associated with a null mutation in the Synechocystis alsS gene. The AlsS enzyme did not complement the isoleucine deficiency of an acetohydroxy acid synthase-deficient Escherichia coli mutant.
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Affiliation(s)
- O Maestri
- Laboratoire de Chimie Bactérienne, CNRS, Marseilles, France
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11
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Yang YT, Peredelchuk M, Bennett GN, San KY. Effect of variation of Klebsiella pneumoniae acetolactate synthase expression on metabolic flux redistribution in Escherichia coli. Biotechnol Bioeng 2000; 69:150-9. [PMID: 10861394 DOI: 10.1002/(sici)1097-0290(20000720)69:2<150::aid-bit4>3.0.co;2-n] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Escherichia coli strains carrying the Bacillus subtilis acetolactate synthase (ALS) gene were previously shown to produce less acetate with higher ATP yields. Metabolic flux analysis was used to show that excess pyruvate was channeled into the less inhibitory product, acetoin. To further understand the role of intrinsic enzymatic properties and the effect of variations in enzyme levels in the alternation of metabolic fluxes, we constructed a chromosomal integrant of the Klebsiella pneumoniae ALS gene. The reported in vitro Michaelis-Menten constants (K(m)) for the Bacillus and the Klebsiella ALS are 13.0 mM and 8.0 mM, respectively. Furthermore, expression of the Klebsiella ALS is under the control of an inducible trp promoter system. Shake-flask experiments showed a linear induction response (the ALS activity changes from about 9 to 223 U/mg of protein when the inducer concentration [IAA] varied from 0 to 40 mg/L). Chemostat experiments showed a similar induction response. Interactions between the branched reactions catalyzed by the PFL, LDH, and the ALS enzymes at the pyruvate node were examined. The results indicate the importance of in vivo enzyme activities in the redistribution of metabolic fluxes.
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Affiliation(s)
- Y T Yang
- Departments of Bioengineering and Chemical Engineering Institute of Biosciences and Bioengineering, Rice University, 6100 Main Street, Houston, Texas 77005-1892, USA
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12
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Chang AK, Duggleby RG. Herbicide-resistant forms of Arabidopsis thaliana acetohydroxyacid synthase: characterization of the catalytic properties and sensitivity to inhibitors of four defined mutants. Biochem J 1998; 333 ( Pt 3):765-77. [PMID: 9677339 PMCID: PMC1219643 DOI: 10.1042/bj3330765] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Acetohydroxyacid synthase (AHAS) catalyses the first step in the synthesis of the branched-chain amino acids and is the target of several classes of herbicides. Four mutants (A122V, W574S, W574L and S653N) of the AHAS gene from Arabidopsis thaliana were constructed, expressed in Escherichia coli, and the enzymes were purified. Each mutant form and wild-type was characterized with respect to its catalytic properties and sensitivity to nine herbicides. Each enzyme had a pH optimum near 7.5. The specific activity varied from 13% (A122V) to 131% (W574L) of the wild-type and the Km for pyruvate of the mutants was similar to the wild-type, except for W574L where it was five-fold higher. The activation by cofactors (FAD, Mg2+ and thiamine diphosphate) was examined. A122V showed reduced affinity for all three cofactors, whereas S653N bound FAD more strongly than wild-type AHAS. Six sulphonylurea herbicides inhibited A122V to a similar degree as the wild-type but S653N showed a somewhat greater reduction in sensitivity to these compounds. In contrast, the W574 mutants were insensitive to these sulphonylureas, with increases in the Kiapp (apparent inhibition constant) of several hundred fold. All four mutants were resistant to three imidazolinone herbicides with decreases in sensitivity ranging from 100-fold to more than 1000-fold.
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Affiliation(s)
- A K Chang
- Centre for Protein Structure, Function and Engineering, Department of Biochemistry, The University of Queensland, Brisbane QLD 4072, Australia
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13
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Chipman D, Barak Z, Schloss JV. Biosynthesis of 2-aceto-2-hydroxy acids: acetolactate synthases and acetohydroxyacid synthases. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1385:401-19. [PMID: 9655946 DOI: 10.1016/s0167-4838(98)00083-1] [Citation(s) in RCA: 160] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Two groups of enzymes are classified as acetolactate synthase (EC 4. 1.3.18). This review deals chiefly with the FAD-dependent, biosynthetic enzymes which readily catalyze the formation of acetohydroxybutyrate from pyruvate and 2-oxobutyrate, as well as of acetolactate from two molecules of pyruvate (the ALS/AHAS group). These enzymes are generally susceptible to inhibition by one or more of the branched-chain amino acids which are ultimate products of the acetohydroxyacids, as well as by several classes of herbicides (sulfonylureas, imidazolinones and others). Some ALS/AHASs also catalyze the (non-physiological) oxidative decarboxylation of pyruvate, leading to peracetic acid; the possible relationship of this process to oxygen toxicity is considered. The bacterial ALS/AHAS which have been well characterized consist of catalytic subunits (around 60 kDa) and smaller regulatory subunits in an alpha2beta2 structure. In the case of Escherichia coli isozyme III, assembly and dissociation of the holoenzyme has been studied. The quaternary structure of the eukaryotic enzymes is less clear and in plants and yeast only catalytic polypeptides (homologous to those of bacteria) have been clearly identified. The presence of regulatory polypeptides in these organisms cannot be ruled out, however, and genes which encode putative ALS/AHAS regulatory subunits have been identified in some cases. A consensus sequence can be constructed from the 21 sequences which have been shown experimentally to represent ALS/AHAS catalytic polypeptides. Many other sequences fit this consensus, but some genes identified as putative 'acetolactate synthase genes' are almost certainly not ALS/AHAS. The solution of the crystal structures of several thiamin diphosphate (ThDP)-dependent enzymes which are homologous to ALS/AHAS, together with the availability of many amino acid sequences for the latter enzymes, has made it possible for two laboratories to propose similar, reasonable models for a dimer of catalytic subunits of an ALS/AHAS. A number of characteristics of these enzymes can now be better understood on the basis of such models: the nature of the herbicide binding site, the structural role of FAD and the binding of ThDP-Mg2+. The models are also guides for experimental testing of ideas concerning structure-function relationships in these enzymes, e.g. the nature of the substrate recognition site. Among the important remaining questions is how the enzyme suppresses alternative reactions of the intrinsically reactive hydroxyethylThDP enamine formed by the decarboxylation of the first substrate molecule and specifically promotes its condensation with 2-oxobutyrate or pyruvate.
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Affiliation(s)
- D Chipman
- Department of Life Sciences, Ben Gurion University of the Negev, Beer Sheva, Israel.
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14
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Hill CM, Pang SS, Duggleby RG. Purification of Escherichia coli acetohydroxyacid synthase isoenzyme II and reconstitution of active enzyme from its individual pure subunits. Biochem J 1997; 327 ( Pt 3):891-8. [PMID: 9581571 PMCID: PMC1218872 DOI: 10.1042/bj3270891] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The first step in the biosynthesis of branched-chain amino acids is catalysed by acetohydroxyacid synthase (EC 4.1.3.18). The reaction involves the decarboxylation of pyruvate followed by condensation with either a second molecule of pyruvate or with 2-oxobutyrate. The enzyme requires as cofactors thiamine diphosphate, a divalent metal ion and, usually, FAD. In most bacteria the enzyme is a heterotetramer of two large and two small subunits. Escherichia coli contains three active isoenzymes and the present study concerns isoenzyme II, whose large and small subunits are encoded by the ilvG and ilvM genes respectively. Cloning these genes into a plasmid vector and overexpression in E. coli allowed a two-step purification procedure for the native enzyme to be developed. The level of expression is considerably higher from a vector that introduces a 50 residue N-terminal fusion containing an oligohistidine sequence on the large subunit. Purification to homogeneity was achieved in a single step by immobilized-metal-affinity chromatography. The kinetic properties of the native and fusion enzyme are indistinguishable with respect to the substrate pyruvate and the inhibitor chlorsulfuron. The individual subunits were expressed as oligohistidine-tagged fusion proteins and each was purified in a single step. Neither subunit alone has significant enzymic activity but, on mixing, the enzyme is reconstituted. The kinetic properties of the reconstituted enzyme are very similar to those of the fusion enzyme. It is proposed that the reconstitution pathway involves successive, and highly co-operative, binding of two small subunit monomers to a large subunit dimer. None of the cofactors is needed for subunit association although they are necessary for the restoration of enzymic activity.
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Affiliation(s)
- C M Hill
- Centre for Protein Structure, Function and Engineering, Department of Biochemistry, University of Queensland, Brisbane 4072, Australia
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Abstract
Acetolactate synthase catalyses the first step in branched-chain amino acid biosynthesis. The bacterial enzyme contains two large and two small subunits but there is only limited and circumstantial evidence for a small subunit in the eukaryotic enzyme. Here this evidence is summarised and protein sequences of two putative eukaryotic small subunits, from a yeast and a red alga, are presented.
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Affiliation(s)
- R G Duggleby
- Centre for Protein Structure, Function and Engineering, Department of Biochemistry, University of Queensland, Brisbane, Australia.
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Phalip V, Schmitt P, Divi�s C. Purification and characterization of the catabolic ?-acetolactate synthase from Leuconostoc mesenteroides subsp. cremoris. Curr Microbiol 1995. [DOI: 10.1007/bf00314587] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Deng WL, Chang HY, Peng HL. Acetoin catabolic system of Klebsiella pneumoniae CG43: sequence, expression, and organization of the aco operon. J Bacteriol 1994; 176:3527-35. [PMID: 8206829 PMCID: PMC205540 DOI: 10.1128/jb.176.12.3527-3535.1994] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
A cosmid clone which was capable of depleting acetoin in vivo was isolated from a library of Klebsiella pneumoniae CG43 cosmids. The smallest functional subclone contained a 3.9-kb DNA fragment of the cosmid clone. Sequencing of the DNA fragment revealed three open reading frames (ORFs A, B, and C) encoding polypeptides of 34, 36, and 52 kDa, respectively. The presence of these proteins was demonstrated by expression of the recombinant DNA clone in Escherichia coli. Considerable similarities between the deduced amino acid sequences of the ORFs and those of the following enzymes were found: acetoin dissimilation enzymes, pyruvate dehydrogenase complex, 2-oxoglutarate dehydrogenase complex, and branched-chain 2-oxo acid dehydrogenase complex of various origins. Activities of these enzymes, including acetoin-dependent dichlorophenolin-dohenol oxidoreductase and dihydrolipoamide acetyltransferase, were detected in the extracts of E. coli harboring the genes encoding products of the three ORFs. Although not required for acetoin depletion in vivo, a possible fourth ORF (ORF D), located 39 nucleotides downstream of ORF C, was also identified. The deduced N-terminal sequence of the ORF D product was highly homologous to the dihydrolipoamide dehydrogenases of several organisms. Primer extension analysis identified the transcriptional start of the operon as an A residue 72 nucleotides upstream of ORF A.
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Affiliation(s)
- W L Deng
- Department of Microbiology and Immunology, Chang Gung College of Medicine and Technology, Tao Yuan, Taiwan
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Candy JM, Duggleby RG. Investigation of the cofactor-binding site of Zymomonas mobilis pyruvate decarboxylase by site-directed mutagenesis. Biochem J 1994; 300 ( Pt 1):7-13. [PMID: 8198554 PMCID: PMC1138114 DOI: 10.1042/bj3000007] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Several enzymes require thiamin diphosphate (ThDP) as an essential cofactor, and we have used one of these, pyruvate decarboxylase (PDC; EC 4.1.1.1) from Zymomonas mobilis, as a model for this group of enzymes. It is well suited for this purpose because of its stability, ease of purification and its simple kinetic properties. A sequence motif of approx. 30 residues, beginning with a glycine-aspartate-glycine (-GDG-) triplet and ending with a double asparagine (-NN-) sequence, has been identified in many of these enzymes [Hawkins, Borges and Perham (1989) FEBS Lett. 255, 77-82]. Other residues within this putative ThDP-binding motif are conserved, but to a lesser extent, including a glutamate and a proline residue. The role of the elements of this motif has been clarified by the determination of the three-dimensional structure of three of these enzymes [Muller, Lindqvist, Furey, Schulz, Jordan and Schneider (1993) Structure 1, 95-103]. Four of the residues within this motif were modified by site-directed mutagenesis of the cloned PDC gene to evaluate their role in cofactor binding. The mutant proteins were expressed in Escherichia coli and found to purify normally, indicating that the tertiary structure of these enzymes had not been grossly perturbed by the amino acid substitutions. We have shown previously [Diefenbach, Candy, Mattick and Duggleby (1992) FEBS Lett. 296, 95-98] that changing the aspartate in the -GDG- sequence to glycine, threonine or asparagine yields an inactive enzyme that is unable to bind ThDP, therefore verifying the role of the ThDP-binding motif. Here we demonstrate that substitution with glutamate yields an active enzyme with a greatly reduced affinity for both ThDP and Mg2+, but with normal kinetics for pyruvate. Unlike the wild-type tetrameric enzyme, this mutant protein usually exists as a dimer. Replacement of the second asparagine of the -NN- sequence by glutamine also yields an inactive enzyme which is unable to bind ThDP, whereas replacement with an aspartate residue results in an active enzyme with a reduced affinity for ThDP but which displays normal kinetics for both Mg2+ and pyruvate. Replacing the conserved glutamate with aspartate did not alter the properties of the enzyme, while the conserved proline, thought to be required for structural reasons, could be substituted with glycine or alanine without inactivating the enzyme, but these changes did reduce its stability.
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Affiliation(s)
- J M Candy
- Department of Biochemistry, University of Queensland, Brisbane, Australia
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Xing R, Whitman WB. Purification and characterization of the oxygen-sensitive acetohydroxy acid synthase from the archaebacterium Methanococcus aeolicus. J Bacteriol 1994; 176:1207-13. [PMID: 8113159 PMCID: PMC205181 DOI: 10.1128/jb.176.5.1207-1213.1994] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Acetohydroxy acid synthase (EC 4.1.3.18) of the archaebacterium Methanococcus aeolicus was purified 1,150-fold to homogeneity. The molecular weight of the purified enzyme was 125,000, and it contained only one type of subunit (M(r) = 58,000). The amino-terminal sequence had 46 to 57% similarity to those of the large subunits of the eubacterial anabolic enzymes and 37 to 43% similarity to those of the yeast and plant enzymes. The methanococcal enzyme had a pH optimum of 7.6. The pI, estimated by chromatofocusing, was 5.6. Activity required Mg2+ or Mn2+ ions, thiamine pyrophosphate, and a flavin. Flavin adenine dinucleotide, flavin mononucleotide, and riboflavin plus 10 mM phosphate all supported activity. However, activity was strongly inhibited by these flavins at 0.3 mM. The Michaelis constants for pyruvate, MgCl2, MnCl2, thiamine pyrophosphate, flavin adenine dinucleotide, and flavin mononucleotide were 6.8 mM, 0.3 mM, 0.16 mM, 1.6 microM, 0.4 microM, and 1.3 microM, respectively. In cell extracts, the enzyme was sensitive to O2 (half-life = 2.7 min with 5% O2 in the headspace), but the purified enzyme was less sensitive to O2 (half-life = 78.0 min with 20% O2). Reconstitution of the enzyme with flavin adenine dinucleotide increased the sensitivity to O2. Moreover, in the assay the homogeneous enzyme was rapidly inactivated by O2, and the concentration required for 50% inhibition (I50) was obtained with an atmosphere of 0.11% O2. The methanococcal enzyme has similarities to the eubacterial and eucaryotic enzymes, consistent with the ancient origin of the archaebacterial enzyme.
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Affiliation(s)
- R Xing
- Department of Microbiology, University of Georgia, Athens 30602-2605
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Phalip V, Schmitt P, Diviès C. A method for screening diacetyl and acetoin-producing bacteria on agar plates. J Basic Microbiol 1994. [DOI: 10.1002/jobm.3620340412] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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