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Richardson BC, Turlington ZR, Vaz Ferreira de Macedo S, Phillips SK, Perry K, Brancato SG, Cooke EW, Gwilt JR, Dasovich MA, Roering AJ, Rossi FM, Snider MJ, French JB, Hicks KA. Structural and Functional Characterization of a Novel Class A Flavin Monooxygenase from Bacillus niacini. Biochemistry 2024. [PMID: 39265075 DOI: 10.1021/acs.biochem.4c00306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/14/2024]
Abstract
A gene cluster responsible for the degradation of nicotinic acid (NA) in Bacillus niacini has recently been identified, and the structures and functions of the resulting enzymes are currently being evaluated to establish pathway intermediates. One of the genes within this cluster encodes a flavin monooxygenase (BnFMO) that is hypothesized to catalyze a hydroxylation reaction. Kinetic analyses of the recombinantly purified BnFMO suggest that this enzyme catalyzes the hydroxylation of 2,6-dihydroxynicotinic acid (2,6-DHNA) or 2,6-dihydroxypyridine (2,6-DHP), which is formed spontaneously by the decarboxylation of 2,6-DHNA. To understand the details of this hydroxylation reaction, we determined the structure of BnFMO using a multimodel approach combining protein X-ray crystallography and cryo-electron microscopy (cryo-EM). A liganded BnFMO cryo-EM structure was obtained in the presence of 2,6-DHP, allowing us to make predictions about potential catalytic residues. The structural data demonstrate that BnFMO is trimeric, which is unusual for Class A flavin monooxygenases. In both the electron density and coulomb potential maps, a region at the trimeric interface was observed that was consistent with and modeled as lipid molecules. High-resolution mass spectral analysis suggests that there is a mixture of phosphatidylethanolamine and phosphatidylglycerol lipids present. Together, these data provide insights into the molecular details of the central hydroxylation reaction unique to the aerobic degradation of NA in Bacillus niacini.
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Affiliation(s)
- Brian C Richardson
- The Hormel Institute, University of Minnesota, Austin, Minnesota 55912, United States
| | - Zachary R Turlington
- Department of Chemistry, State University of New York at Cortland, Cortland, New York 13045, United States
| | | | - Sara K Phillips
- Department of Chemistry, State University of New York at Cortland, Cortland, New York 13045, United States
| | - Kay Perry
- NE-CAT and Department of Chemistry and Chemical Biology, Cornell University, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - Savannah G Brancato
- Department of Chemistry, State University of New York at Cortland, Cortland, New York 13045, United States
| | - Emmalee W Cooke
- Department of Chemistry, State University of New York at Cortland, Cortland, New York 13045, United States
- Department of Chemistry, the College of Wooster, Wooster, Ohio 44691, United States
| | - Jonathan R Gwilt
- Department of Chemistry, State University of New York at Cortland, Cortland, New York 13045, United States
| | - Morgan A Dasovich
- Department of Chemistry, the College of Wooster, Wooster, Ohio 44691, United States
| | - Andrew J Roering
- Department of Chemistry, State University of New York at Cortland, Cortland, New York 13045, United States
| | - Francis M Rossi
- Department of Chemistry, State University of New York at Cortland, Cortland, New York 13045, United States
| | - Mark J Snider
- Department of Chemistry, the College of Wooster, Wooster, Ohio 44691, United States
| | - Jarrod B French
- The Hormel Institute, University of Minnesota, Austin, Minnesota 55912, United States
| | - Katherine A Hicks
- Department of Chemistry, State University of New York at Cortland, Cortland, New York 13045, United States
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2
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Launay R, Chobert SC, Abby SS, Pierrel F, André I, Esque J. Structural Reconstruction of E. coli Ubi Metabolon Using an AlphaFold2-Based Computational Framework. J Chem Inf Model 2024; 64:5175-5193. [PMID: 38710096 DOI: 10.1021/acs.jcim.4c00304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/08/2024]
Abstract
Ubiquinone (UQ) is a redox polyisoprenoid lipid found in the membranes of bacteria and eukaryotes that has important roles, notably one in respiratory metabolism, which sustains cellular bioenergetics. In Escherichia coli, several steps of the UQ biosynthesis take place in the cytosol. To perform these reactions, a supramolecular assembly called Ubi metabolon is involved. This latter is composed of seven proteins (UbiE, UbiG, UbiF, UbiH, UbiI, UbiJ, and UbiK), and its structural organization is unknown as well as its protein stoichiometry. In this study, a computational framework has been designed to predict the structure of this macromolecular assembly. In several successive steps, we explored the possible protein interactions as well as the protein stoichiometry, to finally obtain a structural organization of the complex. The use of AlphaFold2-based methods combined with evolutionary information enabled us to predict several models whose quality and confidence were further analyzed using different metrics and scores. Our work led to the identification of a "core assembly" that will guide functional and structural characterization of the Ubi metabolon.
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Affiliation(s)
- Romain Launay
- Toulouse Biotechnology Institute, TBI, Université de Toulouse, CNRS, INRAE, INSA, 31077 Toulouse, France
| | - Sophie-Carole Chobert
- Univ. Grenoble Alpes, CNRS, UMR 5525, VetAgro Sup, Grenoble INP, TIMC, 38000 Grenoble, France
| | - Sophie S Abby
- Univ. Grenoble Alpes, CNRS, UMR 5525, VetAgro Sup, Grenoble INP, TIMC, 38000 Grenoble, France
| | - Fabien Pierrel
- Univ. Grenoble Alpes, CNRS, UMR 5525, VetAgro Sup, Grenoble INP, TIMC, 38000 Grenoble, France
| | - Isabelle André
- Toulouse Biotechnology Institute, TBI, Université de Toulouse, CNRS, INRAE, INSA, 31077 Toulouse, France
| | - Jérémy Esque
- Toulouse Biotechnology Institute, TBI, Université de Toulouse, CNRS, INRAE, INSA, 31077 Toulouse, France
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3
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Ouyang X, Liu G, Guo L, Wu G, Xu P, Zhao YL, Tang H. A multifunctional flavoprotein monooxygenase HspB for hydroxylation and C-C cleavage of 6-hydroxy-3-succinoyl-pyridine. Appl Environ Microbiol 2024; 90:e0225523. [PMID: 38415602 PMCID: PMC10952382 DOI: 10.1128/aem.02255-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2023] [Accepted: 01/26/2024] [Indexed: 02/29/2024] Open
Abstract
Flavoprotein monooxygenases catalyze reactions, including hydroxylation and epoxidation, involved in the catabolism, detoxification, and biosynthesis of natural substrates and industrial contaminants. Among them, the 6-hydroxy-3-succinoyl-pyridine (HSP) monooxygenase (HspB) from Pseudomonas putida S16 facilitates the hydroxylation and C-C bond cleavage of the pyridine ring in nicotine. However, the mechanism for biodegradation remains elusive. Here, we refined the crystal structure of HspB and elucidated the detailed mechanism behind the oxidative hydroxylation and C-C cleavage processes. Leveraging structural information about domains for binding the cofactor flavin adenine dinucleotide (FAD) and HSP substrate, we used molecular dynamics simulations and quantum/molecular mechanics calculations to demonstrate that the transfer of an oxygen atom from the reactive FAD peroxide species (C4a-hydroperoxyflavin) to the C3 atom in the HSP substrate constitutes a rate-limiting step, with a calculated reaction barrier of about 20 kcal/mol. Subsequently, the hydrogen atom was rebounded to the FAD cofactor, forming C4a-hydroxyflavin. The residue Cys218 then catalyzed the subsequent hydrolytic process of C-C cleavage. Our findings contribute to a deeper understanding of the versatile functions of flavoproteins in the natural transformation of pyridine and HspB in nicotine degradation.IMPORTANCEPseudomonas putida S16 plays a pivotal role in degrading nicotine, a toxic pyridine derivative that poses significant environmental challenges. This study highlights a key enzyme, HspB (6-hydroxy-3-succinoyl-pyridine monooxygenase), in breaking down nicotine through the pyrrolidine pathway. Utilizing dioxygen and a flavin adenine dinucleotide cofactor, HspB hydroxylates and cleaves the substrate's side chain. Structural analysis of the refined HspB crystal structure, combined with state-of-the-art computations, reveals its distinctive mechanism. The crucial function of Cys218 was never discovered in its homologous enzymes. Our findings not only deepen our understanding of bacterial nicotine degradation but also open avenues for applications in both environmental cleanup and pharmaceutical development.
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Affiliation(s)
- Xingyu Ouyang
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Gongquan Liu
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Lihua Guo
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Geng Wu
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Ping Xu
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Yi-Lei Zhao
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
| | - Hongzhi Tang
- State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
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4
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Boiangiu RS, Brinza I, Honceriu I, Mihasan M, Hritcu L. Insights into Pharmacological Activities of Nicotine and 6-Hydroxy-L-nicotine, a Bacterial Nicotine Derivative: A Systematic Review. Biomolecules 2023; 14:23. [PMID: 38254623 PMCID: PMC10813004 DOI: 10.3390/biom14010023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Revised: 12/13/2023] [Accepted: 12/20/2023] [Indexed: 01/24/2024] Open
Abstract
The purported cognitive benefits associated with nicotine and its metabolites in the brain are a matter of debate. In this review, the impact of the pharmacologically active metabolite of a nicotine derivative produced by bacteria named 6-hydroxy-L-nicotine (6HLN) on memory, oxidative stress, and the activity of the cholinergic system in the brain was examined. A search in the PubMed, Science Direct, Web of Science, and Google Scholar databases, limiting entries to those published between 1992 and 2023, was conducted. The search focused specifically on articles about nicotine metabolites, memory, oxidative stress, and cholinergic system activity, as well as enzymes or pathways related to nicotine degradation in bacteria. The preliminary search resulted in 696 articles, and following the application of exclusion criteria, 212 articles were deemed eligible for inclusion. This review focuses on experimental studies supporting nicotine catabolism in bacteria, and the chemical and pharmacological activities of nicotine and its metabolite 6HLN.
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Affiliation(s)
| | | | | | - Marius Mihasan
- BioActive Research Group, Department of Biology, Faculty of Biology, Alexandru Ioan Cuza University of Iasi, 700506 Iasi, Romania; (R.S.B.); (I.B.); (I.H.)
| | - Lucian Hritcu
- BioActive Research Group, Department of Biology, Faculty of Biology, Alexandru Ioan Cuza University of Iasi, 700506 Iasi, Romania; (R.S.B.); (I.B.); (I.H.)
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5
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Brandão TAS, Vieira LA, de Araújo SS, Nagem RAP. Probing the mechanism of flavin action in the oxidative decarboxylation catalyzed by salicylate hydroxylase. Methods Enzymol 2023; 685:241-277. [PMID: 37245904 DOI: 10.1016/bs.mie.2023.03.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Salicylate hydroxylase (NahG) is a FAD-dependent monooxygenase in which the reduced flavin activates O2 coupled to the oxidative decarboxylation of salicylate to catechol or uncoupled from substrate oxidation to afford H2O2. This chapter presents different methodologies in equilibrium studies, steady-state kinetics, and identification of reaction products, which were important to understand the SEAr mechanism of catalysis in NahG, the role of the different FAD parts for ligand binding, the extent of uncoupled reaction, and the catalysis of salicylate's oxidative decarboxylation. These features are likely familiar to many other FAD-dependent monooxygenases and offer a potential asset for developing new tools and strategies in catalysis.
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Affiliation(s)
- Tiago A S Brandão
- Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
| | - Lucas A Vieira
- Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | - Simara S de Araújo
- Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil; Departamento de Bioquímica e Imunologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | - Ronaldo A P Nagem
- Departamento de Bioquímica e Imunologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
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6
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Discovery and biosynthesis of karnamicins as angiotensin converting enzyme inhibitors. Nat Commun 2023; 14:209. [PMID: 36639377 PMCID: PMC9838390 DOI: 10.1038/s41467-023-35829-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Accepted: 01/04/2023] [Indexed: 01/15/2023] Open
Abstract
Angiotensin-converting enzyme inhibitors are widely used for treatment of hypertension and related diseases. Here, six karnamicins E1-E6 (1-6), which bear fully substituted hydroxypyridine and thiazole moieties are characterized from the rare actinobacterium Lechevalieria rhizosphaerae NEAU-A2. Through a combination of isotopic labeling, genome mining, and enzymatic characterization studies, the programmed assembly of the fully substituted hydroxypyridine moiety in karnamicin is proposed to be due to sequential operation of a hybrid polyketide synthase-nonribosomal peptide synthetase, two regioselective pyridine ring flavoprotein hydroxylases, and a methyltransferase. Based on AlphaFold protein structures predictions, molecular docking, and site-directed mutagenesis, we find that two pyridine hydroxylases deploy active site residues distinct from other flavoprotein monooxygenases to direct the chemo- and regioselective hydroxylation of the pyridine nucleus. Pleasingly, karnamicins show significant angiotensin-converting enzyme inhibitory activity with IC50 values ranging from 0.24 to 5.81 μM, suggesting their potential use for the treatment of hypertension and related diseases.
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7
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Structural Insights into 6-Hydroxypseudooxynicotine Amine Oxidase from Pseudomonas geniculata N1, the Key Enzyme Involved in Nicotine Degradation. Appl Environ Microbiol 2020; 86:AEM.01559-20. [PMID: 32737127 DOI: 10.1128/aem.01559-20] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Accepted: 07/23/2020] [Indexed: 11/20/2022] Open
Abstract
Bacteria degrade nicotine mainly using pyridine and pyrrolidine pathways. Previously, we discovered a hybrid of the pyridine and pyrrolidine pathways (the VPP pathway) in Pseudomonas geniculata N1 and characterized its key enzyme, 6-hydroxypseudooxynicotine amine oxidase (HisD). It catalyzes oxidative deamination of 6-hydroxypseudooxynicotine to 6-hydroxy-3-succinoylsemialdehyde-pyridine, which is the crucial step connecting upstream and downstream portions of the VPP pathway. We determined the crystal structure of wild-type HisD to 2.6 Å. HisD is a monomer that contains a flavin mononucleotide, an iron-sulfur cluster, and ADP. On the basis of sequence alignment and structure comparison, a difference has been found among HisD, closely related trimethylamine dehydrogenase (TMADH), and histamine dehydrogenase (HADH). The flavin mononucleotide (FMN) cofactor is not covalently bound to any residue, and the FMN isoalloxazine ring is planar in HisD compared to TMADH or HADH, which forms a 6-S-cysteinyl flavin mononucleotide cofactor and has an FMN isoalloxazine ring in a "butterfly bend" conformation. Based on the structure, docking study, and site-directed mutagenesis, the residues Glu60, Tyr170, Asp262, and Trp263 may be involved in substrate binding. The expanded understanding of the substrate binding mode from this study may guide rational engineering of such enzymes for biodegradation of potential pollutants or for bioconversion to generate desired products.IMPORTANCE Nicotine is a major tobacco alkaloid in tobacco waste. Pyridine and pyrrolidine pathways are the two best-elucidated nicotine metabolic pathways; Pseudomonas geniculata N1 catabolizes nicotine via a hybrid between the pyridine and pyrrolidine pathways. The crucial enzyme, 6-hydroxypseudooxynicotine amine oxidase (HisD), links the upstream and downstream portions of the VPP pathway; however, there is little structural information about this important enzyme. In this study, we determined the crystal structure of HisD from Pseudomonas geniculata N1. Its basic insights about the structure may help us to guide the engineering of such enzymes for bioremediation and bioconversion applications.
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8
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Manenda MS, Picard MÈ, Zhang L, Cyr N, Zhu X, Barma J, Pascal JM, Couture M, Zhang C, Shi R. Structural analyses of the Group A flavin-dependent monooxygenase PieE reveal a sliding FAD cofactor conformation bridging OUT and IN conformations. J Biol Chem 2020; 295:4709-4722. [PMID: 32111738 DOI: 10.1074/jbc.ra119.011212] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Revised: 02/26/2020] [Indexed: 02/02/2023] Open
Abstract
Group A flavin-dependent monooxygenases catalyze the cleavage of the oxygen-oxygen bond of dioxygen, followed by the incorporation of one oxygen atom into the substrate molecule with the aid of NADPH and FAD. These flavoenzymes play an important role in many biological processes, and their most distinct structural feature is the choreographed motions of flavin, which typically adopts two distinct conformations (OUT and IN) to fulfill its function. Notably, these enzymes seem to have evolved a delicate control system to avoid the futile cycle of NADPH oxidation and FAD reduction in the absence of substrate, but the molecular basis of this system remains elusive. Using protein crystallography, size-exclusion chromatography coupled to multi-angle light scattering (SEC-MALS), and small-angle X-ray scattering (SEC-SAXS) and activity assay, we report here a structural and biochemical characterization of PieE, a member of the Group A flavin-dependent monooxygenases involved in the biosynthesis of the antibiotic piericidin A1. This analysis revealed that PieE forms a unique hexamer. Moreover, we found, to the best of our knowledge for the first time, that in addition to the classical OUT and IN conformations, FAD possesses a "sliding" conformation that exists in between the OUT and IN conformations. This observation sheds light on the underlying mechanism of how the signal of substrate binding is transmitted to the FAD-binding site to efficiently initiate NADPH binding and FAD reduction. Our findings bridge a gap currently missing in the orchestrated order of chemical events catalyzed by this important class of enzymes.
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Affiliation(s)
- Mahder S Manenda
- Département de Biochimie, de Microbiologie, et de Bio-informatique, PROTEO, Université Laval, Québec G1V 0A6, Canada.,Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, Québec G1V 0A6, Canada
| | - Marie-Ève Picard
- Département de Biochimie, de Microbiologie, et de Bio-informatique, PROTEO, Université Laval, Québec G1V 0A6, Canada.,Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, Québec G1V 0A6, Canada
| | - Liping Zhang
- CAS Key Laboratory of Tropical Marine Bio-resources and Ecology, RNAM Center for Marine Microbiology, Guangdong Key Laboratory of Marine Materia Medica, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, China
| | - Normand Cyr
- Département de biochimie et médecine moléculaire, Université de Montréal, Montréal, Québec H3T 1J4, Canada
| | - Xiaojun Zhu
- Département de Biochimie, de Microbiologie, et de Bio-informatique, PROTEO, Université Laval, Québec G1V 0A6, Canada.,Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, Québec G1V 0A6, Canada
| | - Julie Barma
- Département de Biochimie, de Microbiologie, et de Bio-informatique, PROTEO, Université Laval, Québec G1V 0A6, Canada.,Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, Québec G1V 0A6, Canada
| | - John M Pascal
- Département de biochimie et médecine moléculaire, Université de Montréal, Montréal, Québec H3T 1J4, Canada
| | - Manon Couture
- Département de Biochimie, de Microbiologie, et de Bio-informatique, PROTEO, Université Laval, Québec G1V 0A6, Canada.,Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, Québec G1V 0A6, Canada
| | - Changsheng Zhang
- CAS Key Laboratory of Tropical Marine Bio-resources and Ecology, RNAM Center for Marine Microbiology, Guangdong Key Laboratory of Marine Materia Medica, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, China
| | - Rong Shi
- Département de Biochimie, de Microbiologie, et de Bio-informatique, PROTEO, Université Laval, Québec G1V 0A6, Canada .,Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, Québec G1V 0A6, Canada
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9
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Chenprakhon P, Wongnate T, Chaiyen P. Monooxygenation of aromatic compounds by flavin-dependent monooxygenases. Protein Sci 2020; 28:8-29. [PMID: 30311986 DOI: 10.1002/pro.3525] [Citation(s) in RCA: 59] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2018] [Revised: 10/08/2018] [Accepted: 10/08/2018] [Indexed: 12/12/2022]
Abstract
Many flavoenzymes catalyze hydroxylation of aromatic compounds especially phenolic compounds have been isolated and characterized. These enzymes can be classified as either single-component or two-component flavin-dependent hydroxylases (monooxygenases). The hydroxylation reactions catalyzed by the enzymes in this group are useful for modifying the biological properties of phenolic compounds. This review aims to provide an in-depth discussion of the current mechanistic understanding of representative flavin-dependent monooxygenases including 3-hydroxy-benzoate 4-hydroxylase (PHBH, a single-component hydroxylase), 3-hydroxyphenylacetate 4-hydroxylase (HPAH, a two-component hydroxylase), and other monooxygenases which catalyze reactions in addition to hydroxylation, including 2-methyl-3-hydroxypyridine-5-carboxylate oxygenase (MHPCO, a single-component enzyme that catalyzes aromatic-ring cleavage), and HadA monooxygenase (a two-component enzyme that catalyzes additional group elimination reaction). These enzymes have different unique structural features which dictate their reactivity toward various substrates and influence their ability to stabilize flavin intermediates such as C4a-hydroperoxyflavin. Understanding the key catalytic residues and the active site environments important for governing enzyme reactivity will undoubtedly facilitate future work in enzyme engineering or enzyme redesign for the development of biocatalytic methods for the synthesis of valuable compounds.
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Affiliation(s)
- Pirom Chenprakhon
- Institute for Innovative Learning, Mahidol University, Nakhon Pathom, 73170, Thailand
| | - Thanyaporn Wongnate
- School of Biomolecular Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), Rayong, 21210, Thailand
| | - Pimchai Chaiyen
- School of Biomolecular Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), Rayong, 21210, Thailand.,Department of Biochemistry and Center for Excellence in Protein and Enzyme Technology, Faculty of Science, Mahidol University, Bangkok, 14000, Thailand
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10
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Zhao S, Hu C, Guo L, Li K, Yu H. Isolation of a 3-hydroxypyridine degrading bacterium, Agrobacterium sp. DW-1, and its proposed degradation pathway. AMB Express 2019; 9:65. [PMID: 31102032 PMCID: PMC6525221 DOI: 10.1186/s13568-019-0782-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Accepted: 04/23/2019] [Indexed: 01/02/2023] Open
Abstract
A 3-hydroxypyridine degrading bacterium, designated strain DW-1, was isolated from petroleum contaminated soil in Liao River China. 16S rRNA-based phylogenetic analysis indicates that strain DW-1 belongs to genus Agrobacterium. The optimal cultivation temperature and pH for strain DW-1 with 3-hydroxypyridine were 30 °C and 8.0, respectively. Under optimal conditions, strain DW-1 could completely degrade up to 1500 mg/L of 3-hydroxypyridine in 66 h. The 3-hydroxypyridine degradation pathway of strain DW-1 was suggested by HPLC and LC-MS analysis. The first reaction of 3-hydroxypyridine degradation in strain DW-1 was α-hydroxylation so that the major metabolite 2,5-dihydroxypyridine was produced, and then 2,5-dihydroxypyridine was transformed by a Fe2+-dependent dioxygenase to form N-formylmaleamic acid. N-Formylmaleamic acid will be transformed to maleic acid and fumaric acid through maleamic acid. This is the first report of the 3-hydroxypyridine degradation pathway and the utilization of 3-hydroxypyridine by a Agrobacterium sp. It may be potentially used for the bioremediation of environments polluted with 3-hydroxypyridine.
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Affiliation(s)
- Shuxue Zhao
- Shandong Provincial Key Laboratory of Applied Mycology, College of Life Sciences, Qingdao Agricultural University, 700 Changcheng Road, Chengyang District, Qingdao, 266109 Shandong Province People’s Republic of China
| | - Chunhui Hu
- Shandong Provincial Key Laboratory of Applied Mycology, College of Life Sciences, Qingdao Agricultural University, 700 Changcheng Road, Chengyang District, Qingdao, 266109 Shandong Province People’s Republic of China
- Key Laboratory of Marine Environmental Science and Ecology, Ministry of Education, Ocean University of China, 238 Songling Road, Laoshan District, Qingdao, 266100 Shandong Province People’s Republic of China
| | - Lizhong Guo
- Shandong Provincial Key Laboratory of Applied Mycology, College of Life Sciences, Qingdao Agricultural University, 700 Changcheng Road, Chengyang District, Qingdao, 266109 Shandong Province People’s Republic of China
| | - Kuiran Li
- Key Laboratory of Marine Environmental Science and Ecology, Ministry of Education, Ocean University of China, 238 Songling Road, Laoshan District, Qingdao, 266100 Shandong Province People’s Republic of China
| | - Hao Yu
- Shandong Provincial Key Laboratory of Applied Mycology, College of Life Sciences, Qingdao Agricultural University, 700 Changcheng Road, Chengyang District, Qingdao, 266109 Shandong Province People’s Republic of China
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11
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Nakamoto KD, Perkins SW, Campbell RG, Bauerle MR, Gerwig TJ, Gerislioglu S, Wesdemiotis C, Anderson MA, Hicks KA, Snider MJ. Mechanism of 6-Hydroxynicotinate 3-Monooxygenase, a Flavin-Dependent Decarboxylative Hydroxylase Involved in Bacterial Nicotinic Acid Degradation. Biochemistry 2019; 58:1751-1763. [PMID: 30810301 DOI: 10.1021/acs.biochem.8b00969] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
6-Hydroxynicotinate 3-monooxygenase (NicC) is a Group A FAD-dependent monooxygenase that catalyzes the decarboxylative hydroxylation of 6-hydroxynicotinic acid (6-HNA) to 2,5-dihydroxypyridine (2,5-DHP) with concomitant oxidation of NADH in nicotinic acid degradation by aerobic bacteria. Two mechanisms for the decarboxylative hydroxylation half-reaction have been proposed [Hicks, K., et al. (2016) Biochemistry 55, 3432-3446]. Results with Bordetella bronchiseptica RB50 NicC here show that a homocyclic analogue of 6-HNA, 4-hydroxybenzoic acid (4-HBA), is decarboxylated and hydroxylated by NicC with a 420-fold lower catalytic efficiency than is 6-HNA. The 13( V/ K), measured with wild-type NicC by isotope ratio mass spectrometry following the natural abundance of 13C in the CO2 product, is inverse for both 6-HNA (0.9989 ± 0.0002) and 4-HBA (0.9942 ± 0.0004) and becomes negligible (0.9999 ± 0.0004) for 5-chloro-6-HNA, an analogue that is 10-fold more catalytically efficient than 6-HNA. Covalently bound 6-HNA complexes of NicC are not observed by mass spectrometry. Comparative steady-state kinetic and Kd6HNA analyses of active site NicC variants (C202A, H211A, H302A, H47E, Y215F, and Y225F) identify Tyr215 and His47 as critical determinants both of 6-HNA binding ( KdY215F/ KdWT > 240; KdH47E/ KdWT > 350) and in coupling rates of 2,5-DHP and NAD+ product formation ([2,5-DHP]/[NAD+] = 1.00 (WT), 0.005 (Y215F), and 0.07 (H47E)]. Results of these functional analyses are in accord with an electrophilic aromatic substitution reaction mechanism in which His47-Tyr215 may serve as the general base to catalyze substrate hydroxylation and refine the structural model for substrate binding by NicC.
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Affiliation(s)
- Kent D Nakamoto
- Department of Chemistry , The College of Wooster , Wooster , Ohio 44691 , United States
| | - Scott W Perkins
- Department of Chemistry , The College of Wooster , Wooster , Ohio 44691 , United States
| | - Ryan G Campbell
- Department of Chemistry , The College of Wooster , Wooster , Ohio 44691 , United States
| | - Matthew R Bauerle
- Department of Chemistry , The College of Wooster , Wooster , Ohio 44691 , United States
| | - Tyler J Gerwig
- Department of Chemistry , The College of Wooster , Wooster , Ohio 44691 , United States
| | - Selim Gerislioglu
- Department of Chemistry , University of Akron , Akron , Ohio 44325 , United States
| | - Chrys Wesdemiotis
- Department of Chemistry , University of Akron , Akron , Ohio 44325 , United States
| | - Mark A Anderson
- Institute for Enzyme Research, Department of Biochemistry , University of Wisconsin , Madison , Wisconsin 53726 , United States
| | - Katherine A Hicks
- Department of Chemistry , The State University of New York College at Cortland , Cortland , New York 13045 , United States
| | - Mark J Snider
- Department of Chemistry , The College of Wooster , Wooster , Ohio 44691 , United States
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12
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Westphal AH, Tischler D, Heinke F, Hofmann S, Gröning JAD, Labudde D, van Berkel WJH. Pyridine Nucleotide Coenzyme Specificity of p-Hydroxybenzoate Hydroxylase and Related Flavoprotein Monooxygenases. Front Microbiol 2018; 9:3050. [PMID: 30631308 PMCID: PMC6315137 DOI: 10.3389/fmicb.2018.03050] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Accepted: 11/27/2018] [Indexed: 12/03/2022] Open
Abstract
p-Hydroxybenzoate hydroxylase (PHBH; EC 1.14.13.2) is a microbial group A flavoprotein monooxygenase that catalyzes the ortho-hydroxylation of 4-hydroxybenzoate to 3,4-dihydroxybenzoate with the stoichiometric consumption of NAD(P)H and oxygen. PHBH and related enzymes lack a canonical NAD(P)H-binding domain and the way they interact with the pyridine nucleotide coenzyme has remained a conundrum. Previously, we identified a surface exposed protein segment of PHBH from Pseudomonas fluorescens involved in NADPH binding. Here, we report the first amino acid sequences of NADH-preferring PHBHs and a phylogenetic analysis of putative PHBHs identified in currently available bacterial genomes. It was found that PHBHs group into three clades consisting of NADPH-specific, NAD(P)H-dependent and NADH-preferring enzymes. The latter proteins frequently occur in Actinobacteria. To validate the results, we produced several putative PHBHs in Escherichia coli and confirmed their predicted coenzyme preferences. Based on phylogeny, protein energy profiling and lifestyle of PHBH harboring bacteria we propose that the pyridine nucleotide coenzyme specificity of PHBH emerged through adaptive evolution and that the NADH-preferring enzymes are the older versions of PHBH. Structural comparison and distance tree analysis of group A flavoprotein monooxygenases indicated that a similar protein segment as being responsible for the pyridine nucleotide coenzyme specificity of PHBH is involved in determining the pyridine nucleotide coenzyme specificity of the other group A members.
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Affiliation(s)
- Adrie H Westphal
- Laboratory of Biochemistry, Wageningen University and Research, Wageningen, Netherlands
| | - Dirk Tischler
- Interdisziplinäres Ökologisches Zentrum, Technische Universität Bergakademie Freiberg, Freiberg, Germany
| | - Florian Heinke
- Bioinformatics Group Mittweida, University of Applied Sciences Mittweida, Mittweida, Germany
| | - Sarah Hofmann
- Interdisziplinäres Ökologisches Zentrum, Technische Universität Bergakademie Freiberg, Freiberg, Germany
| | - Janosch A D Gröning
- Interdisziplinäres Ökologisches Zentrum, Technische Universität Bergakademie Freiberg, Freiberg, Germany
| | - Dirk Labudde
- Bioinformatics Group Mittweida, University of Applied Sciences Mittweida, Mittweida, Germany
| | - Willem J H van Berkel
- Laboratory of Biochemistry, Wageningen University and Research, Wageningen, Netherlands
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13
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Fitzpatrick PF. The enzymes of microbial nicotine metabolism. Beilstein J Org Chem 2018; 14:2295-2307. [PMID: 30202483 PMCID: PMC6122326 DOI: 10.3762/bjoc.14.204] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Accepted: 08/20/2018] [Indexed: 12/27/2022] Open
Abstract
Because of nicotine's toxicity and the high levels found in tobacco and in the waste from tobacco processing, there is a great deal of interest in identifying bacteria capable of degrading it. A number of microbial pathways have been identified for nicotine degradation. The first and best-understood is the pyridine pathway, best characterized for Arthrobacter nicotinovorans, in which the first reaction is hydroxylation of the pyridine ring. The pyrrolidine pathway, which begins with oxidation of a carbon-nitrogen bond in the pyrrolidine ring, was subsequently characterized in a number of pseudomonads. Most recently, a hybrid pathway has been described, which incorporates the early steps in the pyridine pathway and ends with steps in the pyrrolidine pathway. This review summarizes the present status of our understanding of these pathways, focusing on what is known about the individual enzymes involved.
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Affiliation(s)
- Paul F Fitzpatrick
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center, San Antonio, TX, 78229, USA
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14
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Chen M, Zhang Y, Du Y, Zhao Q, Zhang Q, Wu J, Liu W. Enzymatic competition and cooperation branch the caerulomycin biosynthetic pathway toward different 2,2'-bipyridine members. Org Biomol Chem 2018. [PMID: 28649680 DOI: 10.1039/c7ob01284e] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this study, we characterized CaeB6 as a selective hydroxylase and CaeG1 as an O-methyltransferase in the biosynthesis of the 2,2'-bipyridine natural products caerulomycins (CAEs). The C3-hydroxylation activity of CaeB6 competes with the C4-O-methylation activity of CaeG1 and thereby branches the CAE pathway from a common C4-O-demethylated 2,2'-bipyridine intermediate. CaeG1-catalyzed C4-O-methylation leads to a main route that produces the major product CAE-A in Actinoalloteichus cyanogriseus NRRL B-2194. In contrast, CaeB6-catalyzed C3-hydroxylation results in a shunt route in which CaeG1 causes C4-O-methylation and subsequent C3-O-methylation to produce a series of minor CAE products. These findings provide new insights into the biosynthetic pathway of CAEs and a synthetic biology strategy for the selective functionalization of the 2,2'-bipyridine core.
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Affiliation(s)
- Ming Chen
- State Key Laboratory of Bioorganic and Nature Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China.
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15
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Hicks KA, Yuen ME, Zhen WF, Gerwig TJ, Story RW, Kopp MC, Snider MJ. Structural and Biochemical Characterization of 6-Hydroxynicotinic Acid 3-Monooxygenase, A Novel Decarboxylative Hydroxylase Involved in Aerobic Nicotinate Degradation. Biochemistry 2016; 55:3432-46. [DOI: 10.1021/acs.biochem.6b00105] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Katherine A. Hicks
- Department
of Chemistry, SUNY Cortland, Cortland, New York 13045, United States
| | - Meigan E. Yuen
- Department
of Chemistry, SUNY Cortland, Cortland, New York 13045, United States
| | - Wei Feng Zhen
- Department
of Chemistry, SUNY Cortland, Cortland, New York 13045, United States
| | - Tyler J. Gerwig
- Department
of Chemistry, The College of Wooster, Wooster, Ohio 44691, United States
| | - Ryan W. Story
- Department
of Chemistry, The College of Wooster, Wooster, Ohio 44691, United States
| | - Megan C. Kopp
- Department
of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Mark J. Snider
- Department
of Chemistry, The College of Wooster, Wooster, Ohio 44691, United States
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16
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Sucharitakul J, Medhanavyn D, Pakotiprapha D, van Berkel WJH, Chaiyen P. Tyr217 and His213 are important for substrate binding and hydroxylation of 3-hydroxybenzoate 6-hydroxylase fromRhodococcus jostiiRHA1. FEBS J 2016; 283:860-81. [DOI: 10.1111/febs.13636] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Revised: 11/03/2015] [Accepted: 12/21/2015] [Indexed: 01/28/2023]
Affiliation(s)
- Jeerus Sucharitakul
- Department of Biochemistry; Faculty of Dentistry; Chulalongkorn University; Bangkok Thailand
| | - Dheeradhach Medhanavyn
- Department of Biochemistry and Center for Excellence in Proteins and Enzyme Technology; Faculty of Science; Mahidol University; Bangkok Thailand
| | - Danaya Pakotiprapha
- Department of Biochemistry and Center for Excellence in Proteins and Enzyme Technology; Faculty of Science; Mahidol University; Bangkok Thailand
| | | | - Pimchai Chaiyen
- Department of Biochemistry and Center for Excellence in Proteins and Enzyme Technology; Faculty of Science; Mahidol University; Bangkok Thailand
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17
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Luanloet T, Sucharitakul J, Chaiyen P. Selectivity of substrate binding and ionization of 2-methyl-3-hydroxypyridine-5-carboxylic acid oxygenase. FEBS J 2015; 282:3107-25. [PMID: 25639849 DOI: 10.1111/febs.13220] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Revised: 01/21/2015] [Accepted: 01/28/2015] [Indexed: 11/30/2022]
Abstract
2-Methyl-3-hydroxypyridine-5-carboxylic acid (MHPC) oxygenase (EC 1.14.12.4) from Pseudomonas sp. MA-1 is a flavin-dependent monooxygenase that catalyzes a hydroxylation and aromatic ring cleavage reaction. The functional roles of two residues, Tyr223 and Tyr82, located ~ 5 Å away from MHPC, were characterized using site-directed mutagenesis, along with ligand binding, product analysis and transient kinetic experiments. Mutation of Tyr223 resulted in enzyme variants that were impaired in their hydroxylation activity and had Kd values for substrate binding 5-10-fold greater than the wild-type enzyme. Because this residue is adjacent to the water molecule that is located next to the 3-hydroxy group of MHPC, the results indicate that the interaction between Tyr223, H2 O and the 3-hydroxyl group of MHPC are important for substrate binding and hydroxylation. By contrast, the Kd for substrate binding of Tyr82His and Tyr82Phe variants were similar to that of the wild-type enzyme. However, only ~ 40-50% of the substrate was hydroxylated in the reactions of both variants, whereas most of the substrate was hydroxylated in the wild-type enzyme reaction. In free solution, MHPC or 5-hydroxynicotinic acid exists in a mixture of monoanionic and tripolar ionic forms, whereas only the tripolar ionic form binds to the wild-type enzyme. The binding of tripolar ionic MHPC would allow efficient hydroxylation through an electrophilic aromatic substitution mechanism. For the Tyr82His and Tyr82Phe variants, both forms of substrates can bind to the enzymes, indicating that the mutation at Tyr82 abolished the selectivity of the enzyme towards the tripolar ionic form. Transient kinetic studies indicated that the hydroxylation rate constants of both Tyr82 variants are approximately two- to 2.5-fold higher than that of the wild-type enzyme. Altogether, our findings suggest that Tyr82 is important for the binding selectivity of MHPC oxygenase towards the tripolar ionic species, whereas the interaction between Tyr223 and the substrate is important for ensuring hydroxylation. These results highlight how the active site of a flavoenzyme is able to deal with the presence of multiple forms of a substrate in solution and ensure efficient hydroxylation.
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Affiliation(s)
- Thikumporn Luanloet
- Department of Biochemistry and Center of Excellence in Protein Structure & Function, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Jeerus Sucharitakul
- Department of Biochemistry, Faculty of Dentistry, Chulalongkorn University, Bangkok, Thailand
| | - Pimchai Chaiyen
- Department of Biochemistry and Center of Excellence in Protein Structure & Function, Faculty of Science, Mahidol University, Bangkok, Thailand
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18
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Yu H, Hausinger RP, Tang HZ, Xu P. Mechanism of the 6-hydroxy-3-succinoyl-pyridine 3-monooxygenase flavoprotein from Pseudomonas putida S16. J Biol Chem 2014; 289:29158-70. [PMID: 25172510 DOI: 10.1074/jbc.m114.558049] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
6-Hydroxy-3-succinoyl-pyridine (HSP) 3-monooxygenase (HspB), a flavoprotein essential to the pyrrolidine pathway of nicotine degradation, catalyzes pyridine-ring β-hydroxylation, resulting in carbon-carbon cleavage and production of 2,5-dihydroxypyridine. Here, we generated His6-tagged HspB in Escherichia coli, characterized the properties of the recombinant enzyme, and investigated its mechanism of catalysis. In contrast to conclusions reported previously, the second product of the HspB reaction was shown to be succinate, with isotope labeling experiments providing direct evidence that the newly introduced oxygen atom of succinate is derived from H2O. Phylogenetic analysis reveals that HspB is the most closely related to two p-nitrophenol 4-monooxygenases, and the experimental results exhibit that p-nitrophenol is a substrate of HspB. The reduction of HspB (with maxima at 375 and 460 nm, and a shoulder at 485 nm) by NADH was followed by stopped-flow spectroscopy, and the rate constant for reduction was shown to be stimulated by HSP. Reduced HspB reacts with oxygen to form a C(4a)-(hydro)peroxyflavin intermediate with an absorbance maximum at ∼400 nm within the first few milliseconds before converting to the oxidized flavoenzyme species. The formed C(4a)-hydroperoxyflavin intermediate reacts with HSP to form an intermediate that hydrolyzes to the products 2,5-dihydroxypyridine and succinate. The investigation on the catalytic mechanism of a flavoprotein pyridine-ring β-position hydroxylase provides useful information for the biosynthesis of pyridine derivatives.
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Affiliation(s)
- Hao Yu
- From the State Key Laboratory of Microbial Metabolism, and School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China and
| | - Robert P Hausinger
- the Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan 48824
| | - Hong-Zhi Tang
- From the State Key Laboratory of Microbial Metabolism, and School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China and
| | - Ping Xu
- From the State Key Laboratory of Microbial Metabolism, and School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China and
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19
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Gurusamy R, Natarajan S. Current status on biochemistry and molecular biology of microbial degradation of nicotine. ScientificWorldJournal 2013; 2013:125385. [PMID: 24470788 PMCID: PMC3891541 DOI: 10.1155/2013/125385] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2013] [Accepted: 10/14/2013] [Indexed: 11/30/2022] Open
Abstract
Bioremediation is one of the most promising methods to clean up polluted environments using highly efficient potent microbes. Microbes with specific enzymes and biochemical pathways are capable of degrading the tobacco alkaloids including highly toxic heterocyclic compound, nicotine. After the metabolic conversion, these nicotinophilic microbes use nicotine as the sole carbon, nitrogen, and energy source for their growth. Various nicotine degradation pathways such as demethylation pathway in fungi, pyridine pathway in Gram-positive bacteria, pyrrolidine pathway, and variant of pyridine and pyrrolidine pathways in Gram-negative bacteria have been reported. In this review, we discussed the nicotine-degrading pathways of microbes and their enzymes and biotechnological applications of nicotine intermediate metabolites.
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Affiliation(s)
- Raman Gurusamy
- Department of Biotechnology, School of Life Sciences, Pondicherry University, Puducherry 605014, India
| | - Sakthivel Natarajan
- Department of Biotechnology, School of Life Sciences, Pondicherry University, Puducherry 605014, India
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20
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Renck D, Machado P, Souto AA, Rosado LA, Erig T, Campos MM, Farias CB, Roesler R, Timmers LFSM, de Souza ON, Santos DS, Basso LA. Design of novel potent inhibitors of human uridine phosphorylase-1: synthesis, inhibition studies, thermodynamics, and in vitro influence on 5-fluorouracil cytotoxicity. J Med Chem 2013; 56:8892-902. [PMID: 24131420 DOI: 10.1021/jm401389u] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Uridine (Urd) is a promising biochemical modulator to reduce host toxicity caused by 5-fluorouracil (5-FU) without impairing its antitumor activity. Elevated doses of Urd are required to achieve a protective effect against 5-FU toxicity, but exogenous administration of Urd is not well-tolerated. Selective inhibitors of human uridine phosphorylase (hUP) have been proposed as a strategy to increase Urd levels. We describe synthesis and characterization of a new class of ligands that inhibit hUP type 1 (hUP1). The design of ligands was based on a possible SN1 catalytic mechanism and as mimics of the carbocation in the transition state of hUP1. The kinetic and thermodynamic profiles showed that the ligands here presented are the most potent in vitro hUP1 inhibitors developed to date. In addition, a lead compound improved the antiproliferative effects of 5-FU on colon cancer cells, accompanied by a reduction of in vitro 5-FU cytotoxicity in aggressive SW-620 cancer cells.
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Affiliation(s)
- Daiana Renck
- Centro de Pesquisas em Biologia Molecular e Funcional (CPBMF), Pontifícia Universidade Católica do Rio Grande do Sul (PUCRS) , 6681/92-A, TecnoPuc, Av. Ipiranga, 90619-900 Porto Alegre, Rio Grande do Sul, Brazil
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21
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Scott B, Young CA, Saikia S, McMillan LK, Monahan BJ, Koulman A, Astin J, Eaton CJ, Bryant A, Wrenn RE, Finch SC, Tapper BA, Parker EJ, Jameson GB. Deletion and gene expression analyses define the paxilline biosynthetic gene cluster in Penicillium paxilli. Toxins (Basel) 2013; 5:1422-46. [PMID: 23949005 PMCID: PMC3760044 DOI: 10.3390/toxins5081422] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2013] [Revised: 07/22/2013] [Accepted: 08/02/2013] [Indexed: 11/16/2022] Open
Abstract
The indole-diterpene paxilline is an abundant secondary metabolite synthesized by Penicillium paxilli. In total, 21 genes have been identified at the PAX locus of which six have been previously confirmed to have a functional role in paxilline biosynthesis. A combination of bioinformatics, gene expression and targeted gene replacement analyses were used to define the boundaries of the PAX gene cluster. Targeted gene replacement identified seven genes, paxG, paxA, paxM, paxB, paxC, paxP and paxQ that were all required for paxilline production, with one additional gene, paxD, required for regular prenylation of the indole ring post paxilline synthesis. The two putative transcription factors, PP104 and PP105, were not co-regulated with the pax genes and based on targeted gene replacement, including the double knockout, did not have a role in paxilline production. The relationship of indole dimethylallyl transferases involved in prenylation of indole-diterpenes such as paxilline or lolitrem B, can be found as two disparate clades, not supported by prenylation type (e.g., regular or reverse). This paper provides insight into the P. paxilli indole-diterpene locus and reviews the recent advances identified in paxilline biosynthesis.
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Affiliation(s)
- Barry Scott
- Institute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand; E-Mails: (C.A.Y.); (S.S.) (L.K.M.); (B.J.M.); (J.A.); (C.J.E.); (A.B.); (R.E.W.); (E.J.P.); (G.B.J.)
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +64-6-350-5168; Fax: +64-6-350-5688
| | - Carolyn A. Young
- Institute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand; E-Mails: (C.A.Y.); (S.S.) (L.K.M.); (B.J.M.); (J.A.); (C.J.E.); (A.B.); (R.E.W.); (E.J.P.); (G.B.J.)
- The Samuel Roberts Noble Foundation, Ardmore, OK 73401, USA
| | - Sanjay Saikia
- Institute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand; E-Mails: (C.A.Y.); (S.S.) (L.K.M.); (B.J.M.); (J.A.); (C.J.E.); (A.B.); (R.E.W.); (E.J.P.); (G.B.J.)
| | - Lisa K. McMillan
- Institute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand; E-Mails: (C.A.Y.); (S.S.) (L.K.M.); (B.J.M.); (J.A.); (C.J.E.); (A.B.); (R.E.W.); (E.J.P.); (G.B.J.)
| | - Brendon J. Monahan
- Institute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand; E-Mails: (C.A.Y.); (S.S.) (L.K.M.); (B.J.M.); (J.A.); (C.J.E.); (A.B.); (R.E.W.); (E.J.P.); (G.B.J.)
| | - Albert Koulman
- AgResearch, Grasslands Research Centre, Private Bag 11 008, Palmerston North 4442, New Zealand; E-Mails: (A.K.); (B.A.T.)
| | - Jonathan Astin
- Institute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand; E-Mails: (C.A.Y.); (S.S.) (L.K.M.); (B.J.M.); (J.A.); (C.J.E.); (A.B.); (R.E.W.); (E.J.P.); (G.B.J.)
| | - Carla J. Eaton
- Institute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand; E-Mails: (C.A.Y.); (S.S.) (L.K.M.); (B.J.M.); (J.A.); (C.J.E.); (A.B.); (R.E.W.); (E.J.P.); (G.B.J.)
| | - Andrea Bryant
- Institute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand; E-Mails: (C.A.Y.); (S.S.) (L.K.M.); (B.J.M.); (J.A.); (C.J.E.); (A.B.); (R.E.W.); (E.J.P.); (G.B.J.)
| | - Ruth E. Wrenn
- Institute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand; E-Mails: (C.A.Y.); (S.S.) (L.K.M.); (B.J.M.); (J.A.); (C.J.E.); (A.B.); (R.E.W.); (E.J.P.); (G.B.J.)
| | - Sarah C. Finch
- AgResearch, Ruakura Research Centre, East Street, Private Bag 3123, Hamilton 3214, New Zealand; E-Mail:
| | - Brian A. Tapper
- AgResearch, Grasslands Research Centre, Private Bag 11 008, Palmerston North 4442, New Zealand; E-Mails: (A.K.); (B.A.T.)
| | - Emily J. Parker
- Institute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand; E-Mails: (C.A.Y.); (S.S.) (L.K.M.); (B.J.M.); (J.A.); (C.J.E.); (A.B.); (R.E.W.); (E.J.P.); (G.B.J.)
| | - Geoffrey B. Jameson
- Institute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand; E-Mails: (C.A.Y.); (S.S.) (L.K.M.); (B.J.M.); (J.A.); (C.J.E.); (A.B.); (R.E.W.); (E.J.P.); (G.B.J.)
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22
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Montersino S, Orru R, Barendregt A, Westphal AH, van Duijn E, Mattevi A, van Berkel WJH. Crystal structure of 3-hydroxybenzoate 6-hydroxylase uncovers lipid-assisted flavoprotein strategy for regioselective aromatic hydroxylation. J Biol Chem 2013; 288:26235-26245. [PMID: 23864660 DOI: 10.1074/jbc.m113.479303] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
3-Hydroxybenzoate 6-hydroxylase (3HB6H) from Rhodococcus jostii RHA1 is a dimeric flavoprotein that catalyzes the NADH- and oxygen-dependent para-hydroxylation of 3-hydroxybenzoate to 2,5-dihydroxybenzoate. In this study, we report the crystal structure of 3HB6H as expressed in Escherichia coli. The overall fold of 3HB6H is similar to that of p-hydroxybenzoate hydroxylase and other flavoprotein aromatic hydroxylases. Unexpectedly, a lipid ligand is bound to each 3HB6H monomer. Mass spectral analysis identified the ligand as a mixture of phosphatidylglycerol and phosphatidylethanolamine. The fatty acid chains occupy hydrophobic channels that deeply penetrate into the interior of the substrate-binding domain of each subunit, whereas the hydrophilic part is exposed on the protein surface, connecting the dimerization domains via a few interactions. Most remarkably, the terminal part of a phospholipid acyl chain is directly involved in the substrate-binding site. Co-crystallized chloride ion and the crystal structure of the H213S variant with bound 3-hydroxybenzoate provide hints about oxygen activation and substrate hydroxylation. Essential roles are played by His-213 in catalysis and Tyr-105 in substrate binding. This phospholipid-assisted strategy to control regioselective aromatic hydroxylation is of relevance for optimization of flavin-dependent biocatalysts.
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Affiliation(s)
- Stefania Montersino
- From the Laboratory of Biochemistry, Wageningen University, 6703 HA Wageningen, The Netherlands
| | - Roberto Orru
- Department of Biology and Biotechnology, University of Pavia, Via Ferrata 9, 27100 Pavia, Italy, and
| | - Arjan Barendregt
- Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research, and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Adrie H Westphal
- From the Laboratory of Biochemistry, Wageningen University, 6703 HA Wageningen, The Netherlands
| | - Esther van Duijn
- Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research, and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Andrea Mattevi
- Department of Biology and Biotechnology, University of Pavia, Via Ferrata 9, 27100 Pavia, Italy, and.
| | - Willem J H van Berkel
- From the Laboratory of Biochemistry, Wageningen University, 6703 HA Wageningen, The Netherlands,.
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23
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Suemori A. Conserved and non-conserved residues and their role in the structure and function of p-hydroxybenzoate hydroxylase. Protein Eng Des Sel 2013; 26:479-88. [PMID: 23766373 DOI: 10.1093/protein/gzt026] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In order to elucidate the molecular mechanism of the catalytic reaction and enzyme conformation, we substituted 53 conserved residues identified by aligning 92 p-hydroxybenzoate hydroxylase sequences and 19 non-conserved residues selected from crystallographic studies of Pseudomonas fluorescens NBRC14160 p-hydroxybenzoate hydroxylase with 19 other naturally occurring amino acids, yielding a database of 619 active single mutants. The database contained 365 and 254 active single mutants for 44/53 conserved residues and 19 non-conserved residues, respectively; the data included main activity, sub-activity for NADPH and NADPH reaction specificity. Active mutations were not observed for the G14, Q102, G160, E198, R220, R246, N300, F342 and G387 conserved residues, and only one active mutant was obtained at the G9, G11, G187, D286, Y201, R214 and G295 conserved residues and the S13, E32 and R42 non-conserved residues. Only seven active mutants with higher activity than the wild-type enzyme were observed at conserved residues, and only two were observed at non-conserved residues. The 365 mutants at conserved residues included 64 active mutants with higher NADPH reaction specificity than the wild-type enzyme, and some Y181X single mutants exhibited considerable changes in NADPH reaction specificity. A Y181X/L268G double-mutant database was constructed to computationally analyze the effects of these substitutions on structural conformation and function. These results indicated that some conserved or non-conserved residues are important for structural stability or enzyme function.
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Affiliation(s)
- Akio Suemori
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology-AIST, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan.
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24
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Hicks KA, O’Leary SE, Begley TP, Ealick SE. Structural and mechanistic studies of HpxO, a novel flavin adenine dinucleotide-dependent urate oxidase from Klebsiella pneumoniae. Biochemistry 2013; 52:477-87. [PMID: 23259842 PMCID: PMC3552057 DOI: 10.1021/bi301262p] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
HpxO is a flavin-dependent urate oxidase that catalyzes the hydroxylation of uric acid to 5-hydroxyisourate and functions in a novel pathway for purine catabolism found in Klebsiella pneumoniae. We have determined the structures of HpxO with and without uric acid at 2.0 and 2.2 Å, respectively. We have also determined the structure of the R204Q variant at 2.0 Å resolution in the absence of uric acid. The variant structure is very similar to that of wild-type HpxO except for the conformation of Arg103, which interacts with FAD in the variant but not in the wild-type structure. Interestingly, the R204Q variant results in the uncoupling of nicotinamide adenine dinucleotide oxidation from uric acid hydroxylation. This suggests that Arg204 facilitates the deprotonation of uric acid, activating it for the oxygen transfer. On the basis of these data, a mechanism for this reaction consisting of a nucleophilic attack of the urate anion on the flavin hydroperoxide resulting in the formation of 5-hydroxyisourate is proposed.
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Affiliation(s)
- Katherine A. Hicks
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
| | - Seán E. O’Leary
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
- Department of Chemistry, Texas A&M University, College Station, Texas 77842
| | - Tadhg P. Begley
- Department of Chemistry, Texas A&M University, College Station, Texas 77842
| | - Steven E. Ealick
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
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25
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Form follows function: structural and catalytic variation in the class a flavoprotein monooxygenases. Int J Mol Sci 2012; 13:15601-39. [PMID: 23443084 PMCID: PMC3546652 DOI: 10.3390/ijms131215601] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Revised: 11/08/2012] [Accepted: 11/09/2012] [Indexed: 12/02/2022] Open
Abstract
Flavoprotein monooxygenases (FPMOs) exhibit an array of mechanistic solutions to a common chemical objective; the monooxygenation of a target substrate. Each FPMO efficiently couples reduction of a flavin cofactor by NAD(P)H to oxygenation of the target substrate via a (hydro)peroxyflavin intermediate. This purpose of this review is to describe in detail the Class A flavoprotein hydroxylases (FPMO) in the context of the other FPMO classes (B–F). Both one and two component FPMOs are found in nature. Two-component enzymes require, in addition to the monooxygenase, the involvement of a reductase that first catalyzes the reduction of the flavin by NAD(P)H. The Class A and B FPMOs are single-component and manage to orchestrate the same net reaction within a single peptide. The Class A enzymes have, by some considerable margin, the most complete research record. These enzymes use choreographed movements of the flavin ring that facilitate access of the organic substrates to the active site, provide a means for interaction of NADPH with the flavin, offer a mechanism to sequester the dioxygen reduction chemistry from solvent and a means to release the product. The majority of the discrete catalytic events of the catalytic cycle can be observed directly in exquisite detail using spectrophotometric kinetic methods and many of the key mechanistic conclusions are further supported by structural data. This review attempts to compile each of the key observations made for both paradigm and newly discovered examples of Class A FPMOs into a complete catalytic description of one enzymatic turnover.
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26
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Bach RD. Role of the Somersault Rearrangement in the Oxidation Step for Flavin Monooxygenases (FMO). A Comparison between FMO and Conventional Xenobiotic Oxidation with Hydroperoxides. J Phys Chem A 2011; 115:11087-100. [DOI: 10.1021/jp208087u] [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)
- Robert D. Bach
- Department of Chemistry and Biochemistry, University of Delaware, Delaware, United States
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27
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Montersino S, Tischler D, Gassner GT, van Berkel WJH. Catalytic and Structural Features of Flavoprotein Hydroxylases and Epoxidases. Adv Synth Catal 2011. [DOI: 10.1002/adsc.201100384] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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28
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Structure and Mutation Analysis of Archaeal Geranylgeranyl Reductase. J Mol Biol 2011; 409:543-57. [DOI: 10.1016/j.jmb.2011.04.002] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2011] [Revised: 03/26/2011] [Accepted: 04/01/2011] [Indexed: 11/19/2022]
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29
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Tian B, Tu Y, Strid A, Eriksson LA. Hydroxylation and ring-opening mechanism of an unusual flavoprotein monooxygenase, 2-methyl-3-hydroxypyridine-5-carboxylic acid oxygenase: a theoretical study. Chemistry 2010; 16:2557-66. [PMID: 20066695 DOI: 10.1002/chem.200902253] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Hybrid meta-GGA density functional theory (the MPWB1K functional) was used to study the hydroxylation and ring-opening mechanism of 2-methyl-3-hydroxypyridine-5-carboxylic acid oxygenase (MHPCO). This enzyme catalyses the conversion of 2-methyl-3-hydroxypyridine-5-carboxylic acid (MHPC) to alpha-(N-acetylaminomethylene)succinic acid (AAMS), which is the essential ring-opening step in the bacterial degradation of vitamin B(6). MHPCO belongs to the flavin-containing aromatic hydroxylases family. However, MHPCO is capable of catalysing a subsequent aromatic ring-cleavage reaction to give acyclic products rather than hydroxylated aromatic ones. Our calculations show that the re-aromatisation of the hydroxylated intermediate occurs spontaneously in aqueous solution; this implies that the ring-opening process occurs inside the enzyme's active site, in which limited water is available. The instability of the hydroxylated intermediate of MHPCO is the main reason why acyclic products are formed. Previously proposed mechanisms for the ring-opening step were studied, and were shown to be less likely to occur (DeltaDeltaG(not equal298)>35 kcal mol(-1)). Two new pathways with reasonable barrier heights (DeltaDeltaG(not equal 298)<15 kcal mol(-1)) are reported herein, which are in accordance with all experimental information present to date.
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Affiliation(s)
- Boxue Tian
- Orebro Life Science Center School of Science and Technology, Orebro University, 70182 Orebro, Sweden
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30
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McCulloch KM, Mukherjee T, Begley TP, Ealick SE. Structure of the PLP degradative enzyme 2-methyl-3-hydroxypyridine-5-carboxylic acid oxygenase from Mesorhizobium loti MAFF303099 and its mechanistic implications. Biochemistry 2009; 48:4139-49. [PMID: 19317437 DOI: 10.1021/bi900149f] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A vitamin B(6) degradative pathway has recently been identified and characterized in Mesorhizobium loti MAFF303099. One of the enzymes on this pathway, 2-methyl-3-hydroxypyridine-5-carboxylic acid oxygenase (MHPCO), is a flavin-dependent enzyme and catalyzes the oxidative ring-opening of 2-methyl-3-hydroxypyridine-5-carboxylic acid to form E-2-(acetamino-methylene)succinate. The gene for this enzyme has been cloned, and the corresponding protein has been overexpressed in Escherichia coli and purified. The crystal structure of MHPCO has been solved to 2.1 A using SAD phasing with and without the substrate MHPC bound. These crystal structures provide insight into the reaction mechanism and suggest roles for active site residues in the catalysis of a novel oxidative ring-opening reaction.
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Affiliation(s)
- Kathryn M McCulloch
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA
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31
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Buedenbender S, Rachid S, Müller R, Schulz GE. Structure and action of the myxobacterial chondrochloren halogenase CndH: a new variant of FAD-dependent halogenases. J Mol Biol 2008; 385:520-30. [PMID: 19000696 DOI: 10.1016/j.jmb.2008.10.057] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2008] [Revised: 10/11/2008] [Accepted: 10/21/2008] [Indexed: 10/21/2022]
Abstract
The crystal structure of the FAD-dependent chondrochloren halogenase CndH has been established at 2.1 A resolution. The enzyme contains the characteristic FAD-binding scaffold of the glutathione reductase superfamily. Except for its C-terminal domain, the chainfold of CndH is virtually identical with those of FAD-dependent aromatic hydroxylases. When compared to the structurally known FAD-dependent halogenases PrnA and RebH, CndH lacks a 45 residue segment near position 100 and deviates in the C-terminal domain. Both variations are near the active center and appear to reflect substrate differences. Whereas PrnA and RebH modify free tryptophan, CndH halogenates the tyrosyl group of a chondrochloren precursor that is most likely bound to a carrier protein. In contrast to PrnA and RebH, which enclose their small substrate completely, CndH has a large non-polar surface patch that may accommodate the putative carrier. Apart from the substrate binding site, the active center of CndH corresponds to those of PrnA and RebH. At the halogenation site, CndH has the characteristic lysine (Lys76) but lacks the required base Glu346 (PrnA). This base may be supplied by a residue of its C-terminal domain or by the carrier. These differences were corroborated by an overall sequence comparison between the known FAD-dependent halogenases, which revealed a split into a PrnA-RebH group and a CndH group. The two functionally established members of the CndH group use carrier-bound substrates, whereas three members of PrnA-RebH group are known to accept a free amino acid. Given the structural and functional distinction, we classify CndH as a new variant B of the FAD-dependent halogenases, adding a new feature to the structurally established variant A enzymes PrnA and RebH.
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Affiliation(s)
- Stefan Buedenbender
- Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Albertstr. 21, D-79104 Freiburg im Breisgau, Germany
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