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Regiospecific Oxidation of Chlorobenzene to 4-Chlororesorcinol, Chlorohydroquinone, 3-Chlorocatechol and 4-Chlorocatechol by Engineered Toluene o-Xylene Monooxygenases. Appl Environ Microbiol 2022; 88:e0035822. [PMID: 35736230 PMCID: PMC9275245 DOI: 10.1128/aem.00358-22] [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: 12/25/2022] Open
Abstract
Toluene o-xylene monooxygenase (ToMO) was found to oxidize chlorobenzene to form 2-chlorophenol (2-CP, 4%), 3-CP (12%), and 4-CP (84%) with a total product formation rate of 1.2 ± 0.17 nmol/min/mg protein. It was also discovered that ToMO forms 4-chlorocatechol (4-CC) from 3-CP and 4-CP with initial rates of 0.54 ± 0.10 and 0.40 ± 0.04 nmol/min/mg protein, respectively, and chlorohydroquinone (CHQ, 13%), 4-chlororesorcinol (4-CR, 3%), and 3-CC (84%) from 2-CP with an initial product formation rate of 1.1 ± 0.32 nmol/min/mg protein. To increase the oxidation rate and alter the oxidation regiospecificity of chloroaromatics, as well as to study the roles of active site residues L192 and A107 of the alpha hydroxylase fragment of ToMO (TouA), we used the saturation mutagenesis approach of protein engineering. Thirteen TouA variants were isolated, among which some of the best substitutions uncovered here have never been studied before. Specifically, TouA variant L192V was identified which had 1.8-, 1.4-, 2.4-, and 4.8-fold faster hydroxylation activity toward chlorobenzene, 2-CP, 3-CP, and 4-CP, respectively, compared to the native ToMO. The L192V variant also had the regiospecificity of chlorobenzene changed from 4% to 13% 2-CP and produced the novel product 3-CC (4%) from 3-CP. Most of the isolated variants were identified to change the regiospecificity of oxidation. For example, compared to the native ToMO, variants A107T, A107N, and A107M produced 6.3-, 7.0-, and 7.3-fold more 4-CR from 2-CP, respectively, and variants A107G and A107G/L192V produced 3-CC (33 and 39%, respectively) from 3-CP whereas native ToMO did not. IMPORTANCE Chlorobenzene is a commonly used toxic solvent and listed as a priority environmental pollutant by the US Environmental Protection Agency. Here, we report that Escherichia coli TG1 cells expressing toluene o-xylene monooxygenase (ToMO) can successfully oxidize chlorobenzene to form dihydroxy chloroaromatics, which are valuable industrial compounds. ToMO performs this at room temperature in water using only molecular oxygen and a cofactor supplied by the cells. Using protein engineering techniques, we also isolated ToMO variants with enhanced oxidation activity as well as fine-tuned regiospecificities which make direct microbial oxygenations even more attractive. The significance of this work lies in the ability to degrade environmental pollutants while at the same time producing valuable chemicals using environmentally benign biological methods rather than expensive, complex chemical processes.
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2
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Surface residues serine 69 and arginine 194 of metagenome-derived lipase influence catalytic activity. Biochem Eng J 2020. [DOI: 10.1016/j.bej.2019.107442] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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Thompson B, Pugh S, Machas M, Nielsen DR. Muconic Acid Production via Alternative Pathways and a Synthetic "Metabolic Funnel". ACS Synth Biol 2018; 7:565-575. [PMID: 29053259 DOI: 10.1021/acssynbio.7b00331] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Muconic acid is a promising platform biochemical and precursor to adipic acid, which can be used to synthesize various plastics and polymers. In this study, the systematic construction and comparative evaluation of a modular network of non-natural pathways for muconic acid biosynthesis was investigated in Escherichia coli, including via three distinct and novel pathways proceeding via phenol as a common intermediate. However, poor recombinant activity and high promiscuity of phenol hydroxylase ultimately limited "phenol-dependent" muconic acid production. A fourth pathway proceeding via p-hydroxybenzoate, protocatechuate, and catechol was accordingly developed, though with muconic acid titers by this route reaching just 819 mg/L, its performance lagged behind that of the established, "3-dehydroshikimiate-derived" route. Finally, these two most promising pathways were coexpressed in parallel to create a synthetic "metabolic funnel" that, by enabling maximal net precursor assimilation and flux while preserving native chorismate biosynthesis, nearly doubled muconic acid production to up to >3.1 g/L at a glucose yield of 158 mg/g while introducing only a single auxotrophy. This generalizable, "funneling" strategy is expected to have broad applications in metabolic engineering for further enhancing production of muconic acid, as well as other important bioproducts of interest.
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Affiliation(s)
- Brian Thompson
- Chemical Engineering, School for Engineering
of Matter, Transport, and Energy, Arizona State University, Tempe, Arizona 85287, United States
| | - Shawn Pugh
- Chemical Engineering, School for Engineering
of Matter, Transport, and Energy, Arizona State University, Tempe, Arizona 85287, United States
| | - Michael Machas
- Chemical Engineering, School for Engineering
of Matter, Transport, and Energy, Arizona State University, Tempe, Arizona 85287, United States
| | - David R. Nielsen
- Chemical Engineering, School for Engineering
of Matter, Transport, and Energy, Arizona State University, Tempe, Arizona 85287, United States
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4
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Karich A, Ullrich R, Scheibner K, Hofrichter M. Fungal Unspecific Peroxygenases Oxidize the Majority of Organic EPA Priority Pollutants. Front Microbiol 2017; 8:1463. [PMID: 28848501 PMCID: PMC5552789 DOI: 10.3389/fmicb.2017.01463] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Accepted: 07/20/2017] [Indexed: 11/18/2022] Open
Abstract
Unspecific peroxygenases (UPOs) are secreted fungal enzymes with promiscuity for oxygen transfer and oxidation reactions. Functionally, they represent hybrids of P450 monooxygenases and heme peroxidases; phylogenetically they belong to the family of heme-thiolate peroxidases. Two UPOs from the basidiomycetous fungi Agrocybe aegerita (AaeUPO) and Marasmius rotula (MroUPO) converted 35 out of 40 compounds listed as EPA priority pollutants, including chlorinated benzenes and their derivatives, halogenated biphenyl ethers, nitroaromatic compounds, polycyclic aromatic hydrocarbons (PAHs) and phthalic acid derivatives. These oxygenations and oxidations resulted in diverse products and—if at all—were limited for three reasons: (i) steric hindrance caused by multiple substitutions or bulkiness of the compound as such (e.g., hexachlorobenzene or large PAHs), (ii) strong inactivation of aromatic rings (e.g., nitrobenzene), and (iii) low water solubility (e.g., complex arenes). The general outcome of our study is that UPOs can be considered as extracellular counterparts of intracellular monooxygenases, both with respect to catalyzed reactions and catalytic versatility. Therefore, they should be taken into consideration as a relevant biocatalytic detoxification and biodegradation tool used by fungi when confronted with toxins, xenobiotics and pollutants in their natural environments.
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Affiliation(s)
- Alexander Karich
- Department of Bio-and Environmental Sciences, Technische Universität Dresden-International Institute ZittauZittau, Germany
| | - René Ullrich
- Department of Bio-and Environmental Sciences, Technische Universität Dresden-International Institute ZittauZittau, Germany
| | - Katrin Scheibner
- Enzyme Technology Unit, Brandenburg University of TechnologyCottbus, Germany
| | - Martin Hofrichter
- Department of Bio-and Environmental Sciences, Technische Universität Dresden-International Institute ZittauZittau, Germany
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5
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Lock M, Nichol T, Murrell JC, Smith TJ. Mutagenesis and expression of methane monooxygenase to alter regioselectivity with aromatic substrates. FEMS Microbiol Lett 2017; 364:3906680. [PMID: 28854685 PMCID: PMC5812538 DOI: 10.1093/femsle/fnx137] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Accepted: 06/27/2017] [Indexed: 11/13/2022] Open
Abstract
Soluble methane monooxygenase (sMMO) from methane-oxidising bacteria can oxygenate more than 100 hydrocarbons and is one of the most catalytically versatile biological oxidation catalysts. Expression of recombinant sMMO has to date not been achieved in Escherichia coli and so an alternative expression system must be used to manipulate it genetically. Here we report substantial improvements to the previously described system for mutagenesis of sMMO and expression of recombinant enzymes in a methanotroph (Methylosinus trichosporium OB3b) expression system. This system has been utilised to make a number of new mutants and to engineer sMMO to increase its catalytic precision with a specific substrate whilst increasing activity by up to 6-fold. These results are the first 'proof-of-principle' experiments illustrating the feasibility of developing sMMO-derived catalysts for diverse applications.
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Affiliation(s)
- Malcolm Lock
- Biomolecular Sciences Research Centre, Sheffield Hallam University, Sheffield S1 1WB, UK
| | - Tim Nichol
- Biomolecular Sciences Research Centre, Sheffield Hallam University, Sheffield S1 1WB, UK
| | - J. Colin Murrell
- School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK
| | - Thomas J. Smith
- Biomolecular Sciences Research Centre, Sheffield Hallam University, Sheffield S1 1WB, UK
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6
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Kurt C, Sönmez B, Vardar N, Yanık-Yıldırım KC, Vardar-Schara G. Cavity residue leucine 95 and channel residues glutamine 204, aspartic acid 211, and phenylalanine 269 of toluene o-xylene monooxygenase influence catalysis. Appl Microbiol Biotechnol 2016; 100:7599-609. [PMID: 27311562 DOI: 10.1007/s00253-016-7658-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2016] [Revised: 05/27/2016] [Accepted: 05/31/2016] [Indexed: 10/21/2022]
Abstract
Structural analysis of toluene-o-xylene monooxygenase (ToMO) hydroxylase revealed the presence of three hydrophobic cavities, a channel, and a pore leading from the protein surface to the active site. Here, saturation mutagenesis was used to investigate the catalytic roles of alpha-subunit (TouA) second cavity residue L95 and TouA channel residues Q204, D211, and F269. By testing the substrates toluene, phenol, nitrobenzene, and/or naphthalene, these positions were found to influence the catalytic activity of ToMO. Several regiospecific variants were identified from TouA positions Q204, F269, and L95. For example, TouA variant Q204H had the regiospecificity of nitrobenzene changed significantly from 30 to 61 % p-nitrophenol. Interestingly, a combination of mutations at Q204H and A106V altered the regiospecificity of nitrobenzene back to 27 % p-nitrophenol. TouA variants F269Y, F269P, Q204E, and L95D improved the meta-hydroxylating capability of nitrobenzene by producing 87, 85, 82, and 77 % m-nitrophenol, respectively. For naphthalene oxidation, TouA variants F269V, Q204A, Q204S/S222N, and F269T had the regiospecificity changed from 16 to 9, 10, 23, and 25 % 2-naphthol, respectively. Here, two additional TouA residues, S222 and A106, were also identified that may have important roles in catalysis. Most of the isolated variants from D211 remained active, whereas having a hydrophobic residue at this position appeared to diminish the catalytic activity toward naphthalene. The mutational effects on the ToMO regiospecificity described here suggest that it is possible to further fine tune and engineer the reactivity of multicomponent diiron monooxygenases toward different substrates at positions that are relatively distant from the active site.
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Affiliation(s)
- Cansu Kurt
- Department of Genetics and Biongineering, Fatih University, Buyukcekmece, 34500, Istanbul, Turkey
| | - Burcu Sönmez
- Department of Genetics and Biongineering, Fatih University, Buyukcekmece, 34500, Istanbul, Turkey
| | - Nurcan Vardar
- Department of Genetics and Biongineering, Fatih University, Buyukcekmece, 34500, Istanbul, Turkey
| | - K Cansu Yanık-Yıldırım
- Department of Genetics and Biongineering, Fatih University, Buyukcekmece, 34500, Istanbul, Turkey
| | - Gönül Vardar-Schara
- Department of Genetics and Biongineering, Fatih University, Buyukcekmece, 34500, Istanbul, Turkey.
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7
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Nichol T, Murrell JC, Smith TJ. Controlling the Activities of the Diiron Centre in Bacterial Monooxygenases: Lessons from Mutagenesis and Biodiversity. Eur J Inorg Chem 2015. [DOI: 10.1002/ejic.201500043] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Tim Nichol
- Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, UK, http://www.shu.ac.uk/research/bmrc/staff/professor‐tom‐smith
| | - J. Colin Murrell
- School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
| | - Thomas J. Smith
- Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, UK, http://www.shu.ac.uk/research/bmrc/staff/professor‐tom‐smith
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8
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Kingsley LJ, Lill MA. Substrate tunnels in enzymes: structure-function relationships and computational methodology. Proteins 2015; 83:599-611. [PMID: 25663659 DOI: 10.1002/prot.24772] [Citation(s) in RCA: 99] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Revised: 01/08/2015] [Accepted: 01/14/2015] [Indexed: 12/14/2022]
Abstract
In enzymes, the active site is the location where incoming substrates are chemically converted to products. In some enzymes, this site is deeply buried within the core of the protein, and, in order to access the active site, substrates must pass through the body of the protein via a tunnel. In many systems, these tunnels act as filters and have been found to influence both substrate specificity and catalytic mechanism. Identifying and understanding how these tunnels exert such control has been of growing interest over the past several years because of implications in fields such as protein engineering and drug design. This growing interest has spurred the development of several computational methods to identify and analyze tunnels and how ligands migrate through these tunnels. The goal of this review is to outline how tunnels influence substrate specificity and catalytic efficiency in enzymes with buried active sites and to provide a brief summary of the computational tools used to identify and evaluate these tunnels.
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Affiliation(s)
- Laura J Kingsley
- Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, Indiana
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9
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Saturation mutagenesis of Bradyrhizobium sp. BTAi1 toluene 4-monooxygenase at alpha-subunit residues proline 101, proline 103, and histidine 214 for regiospecific oxidation of aromatics. Appl Microbiol Biotechnol 2014; 98:8975-86. [DOI: 10.1007/s00253-014-5913-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2014] [Revised: 06/20/2014] [Accepted: 06/24/2014] [Indexed: 10/25/2022]
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10
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Hosseini A, Brouk M, Lucas MF, Glaser F, Fishman A, Guallar V. Atomic picture of ligand migration in toluene 4-monooxygenase. J Phys Chem B 2014; 119:671-8. [PMID: 24798294 DOI: 10.1021/jp502509a] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Computational modeling combined with mutational and activity assays was used to underline the substrate migration pathways in toluene 4-monooxygenase, a member of the important family of bacterial multicomponent monooxygenases (BMMs). In all structurally defined BMM hydroxylases, several hydrophobic cavities in the α-subunit map a preserved path from the protein surface to the diiron active site. Our results confirm the presence of two pathways by which different aromatic molecules can enter/escape the active site. While the substrate is observed to enter from both channels, the more hydrophilic product is withdrawn mainly from the shorter channel ending at residues D285 and E214. The long channel ends in the vicinity of S395, whose variants have been seen to affect activity and specificity. These mutational effects are clearly reproduced and rationalized by the in silico studies. Furthermore, the combined computational and experimental results highlight the importance of residue F269, which is located at the intersection of the two channels.
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Affiliation(s)
- Ali Hosseini
- Department of Life Sciences, Barcelona Supercomputing Center , Nexus II Building, 08034 Barcelona, Spain
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11
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Sönmez B, Yanık-Yıldırım KC, Wood TK, Vardar-Schara G. The role of substrate binding pocket residues phenylalanine 176 and phenylalanine 196 on Pseudomonas sp. OX1 toluene o-xylene monooxygenase activity and regiospecificity. Biotechnol Bioeng 2014; 111:1506-12. [PMID: 24519264 DOI: 10.1002/bit.25212] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Revised: 12/27/2013] [Accepted: 02/06/2014] [Indexed: 11/10/2022]
Abstract
Saturation mutagenesis was used to generate eleven substitutions of toluene-o-xylene monooxygenase (ToMO) at alpha subunit (TouA) positions F176 and F196 among which nine were novel: F176H, F176N, F176S, F176T, F196A, F196L, F196T, F196Y, F196H, F196I, and F196V. By testing the substrates phenol, toluene, and naphthalene, these positions were found to influence ToMO oxidation activity and regiospecificity. Specifically, TouA variant F176H was identified that had 4.7-, 4.3-, and 1.8-fold faster hydroxylation activity towards phenol, toluene, and naphthalene, respectively, compared to native ToMO. The F176H variant also produced the novel product hydroquinone (61%) from phenol, made twofold more 2-naphthol from naphthalene (34% vs. 16% by the wild-type ToMO), and had the regiospecificity of toluene changed from 51% to 73% p-cresol. The TouA F176N variant had the most para-hydroxylation capability, forming p-cresol (92%) from toluene and hydroquinone (82%) from phenol as the major product, whereas native ToMO formed 30% o-cresol, 19% m-cresol, and 51% of p-cresol from toluene and 100% catechol from phenol. For naphthalene oxidation, TouA variant F176S exhibited the largest shift in the product distribution by producing threefold more 2-naphthol. Among the other F196 variants, F196L produced catechol from phenol two times faster than the wild-type enzyme. The TouA F196I variant produced twofold less o-cresol and 19% more p-cresol from toluene, and the TouA F196A variant produced 62% more 2-naphthol from naphthalene compared to wild-type ToMO. Both of these positions have never been studied through the saturation mutagenesis and some of the best substitutions uncovered here have never been predicted and characterized for aromatics hydroxylation.
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Affiliation(s)
- Burcu Sönmez
- Department of Genetics and Biongineering, Fatih University, Buyukcekmece, Istanbul, 34500, Turkey
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12
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Affiliation(s)
- Artur Gora
- Loschmidt Laboratories,
Department
of Experimental Biology and Research Centre for Toxic Compounds in
the Environment, Faculty of Science, Masaryk University, Kamenice 5/A13, 625 00 Brno, Czech Republic
| | - Jan Brezovsky
- Loschmidt Laboratories,
Department
of Experimental Biology and Research Centre for Toxic Compounds in
the Environment, Faculty of Science, Masaryk University, Kamenice 5/A13, 625 00 Brno, Czech Republic
| | - Jiri Damborsky
- Loschmidt Laboratories,
Department
of Experimental Biology and Research Centre for Toxic Compounds in
the Environment, Faculty of Science, Masaryk University, Kamenice 5/A13, 625 00 Brno, Czech Republic
- International Centre for Clinical
Research, St. Anne’s University Hospital Brno, Pekarska 53, 656 91 Brno, Czech Republic
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13
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The influence of key residues in the tunnel entrance and the active site on activity and selectivity of toluene-4-monooxygenase. ACTA ACUST UNITED AC 2010. [DOI: 10.1016/j.molcatb.2010.03.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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14
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Improving biocatalyst performance by integrating statistical methods into protein engineering. Appl Environ Microbiol 2010; 76:6397-403. [PMID: 20709845 DOI: 10.1128/aem.00878-10] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Directed evolution and rational design were used to generate active variants of toluene-4-monooxygenase (T4MO) on 2-phenylethanol (PEA), with the aim of producing hydroxytyrosol, a potent antioxidant. Due to the complexity of the enzymatic system-four proteins encoded by six genes-mutagenesis is labor-intensive and time-consuming. Therefore, the statistical model of Nov and Wein (J. Comput. Biol. 12:247-282) was used to reduce the number of variants produced and evaluated in a lab. From an initial data set of 24 variants, with mutations at nine positions, seven double or triple mutants were identified through statistical analysis. The average activity of these mutants was 4.6-fold higher than the average activity of the initial data set. In an attempt to further improve the enzyme activity to obtain PEA hydroxylation, a second round of statistical analysis was performed. Nine variants were considered, with 3, 4, and 5 point mutations. The average activity of the variants obtained in the second statistical round was 1.6-fold higher than in the first round and 7.3-fold higher than that of the initial data set. The best variant discovered, TmoA I100A E214G D285Q, exhibited an initial oxidation rate of 4.4 ± 0.3 nmol/min/mg protein, which is 190-fold higher than the rate obtained by the wild type. This rate was also 2.6-fold higher than the activity of the wild type on the natural substrate toluene. By considering only 16 preselected mutants (out of ∼13,000 possible combinations), a highly active variant was discovered with minimum time and effort.
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15
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Molecular approaches in bioremediation. Curr Opin Biotechnol 2008; 19:572-8. [DOI: 10.1016/j.copbio.2008.10.003] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2008] [Revised: 10/14/2008] [Accepted: 10/16/2008] [Indexed: 01/08/2023]
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16
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Halsey KH, Sayavedra-Soto LA, Bottomley PJ, Arp DJ. Site-directed amino acid substitutions in the hydroxylase alpha subunit of butane monooxygenase from Pseudomonas butanovora: Implications for substrates knocking at the gate. J Bacteriol 2006; 188:4962-9. [PMID: 16788204 PMCID: PMC1482983 DOI: 10.1128/jb.00280-06] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2006] [Accepted: 04/22/2006] [Indexed: 11/20/2022] Open
Abstract
Butane monooxygenase (BMO) from Pseudomonas butanovora has high homology to soluble methane monooxygenase (sMMO), and both oxidize a wide range of hydrocarbons; yet previous studies have not demonstrated methane oxidation by BMO. Studies to understand the basis for this difference were initiated by making single-amino-acid substitutions in the hydroxylase alpha subunit of butane monooxygenase (BMOH-alpha) in P. butanovora. Residues likely to be within hydrophobic cavities, adjacent to the diiron center, and on the surface of BMOH-alpha were altered to the corresponding residues from the alpha subunit of sMMO. In vivo studies of five site-directed mutants were carried out to initiate mechanistic investigations of BMO. Growth rates of mutant strains G113N and L279F on butane were dramatically slower than the rate seen with the control P. butanovora wild-type strain (Rev WT). The specific activities of BMO in these strains were sevenfold lower than those of Rev WT. Strains G113N and L279F also showed 277- and 5.5-fold increases in the ratio of the rates of 2-butanol production to 1-butanol production compared to Rev WT. Propane oxidation by strain G113N was exclusively subterminal and led to accumulation of acetone, which P. butanovora could not further metabolize. Methane oxidation was measurable for all strains, although accumulation of 23 microM methanol led to complete inhibition of methane oxidation in strain Rev WT. In contrast, methane oxidation by strain G113N was not completely inhibited until the methanol concentration reached 83 microM. The structural significance of the results obtained in this study is discussed using a three-dimensional model of BMOH-alpha.
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Affiliation(s)
- Kimberly H Halsey
- Molecular and Cellular Biology Program, Oregon State University, Corvallis, OR 97331, USA
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Lalucat J, Bennasar A, Bosch R, García-Valdés E, Palleroni NJ. Biology of Pseudomonas stutzeri. Microbiol Mol Biol Rev 2006; 70:510-47. [PMID: 16760312 PMCID: PMC1489536 DOI: 10.1128/mmbr.00047-05] [Citation(s) in RCA: 325] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Pseudomonas stutzeri is a nonfluorescent denitrifying bacterium widely distributed in the environment, and it has also been isolated as an opportunistic pathogen from humans. Over the past 15 years, much progress has been made in elucidating the taxonomy of this diverse taxonomical group, demonstrating the clonality of its populations. The species has received much attention because of its particular metabolic properties: it has been proposed as a model organism for denitrification studies; many strains have natural transformation properties, making it relevant for study of the transfer of genes in the environment; several strains are able to fix dinitrogen; and others participate in the degradation of pollutants or interact with toxic metals. This review considers the history of the discovery, nomenclatural changes, and early studies, together with the relevant biological and ecological properties, of P. stutzeri.
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Affiliation(s)
- Jorge Lalucat
- Department de Biologia, Microbiologia, Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain.
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18
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Vardar G, Tao Y, Lee J, Wood TK. Alanine 101 and alanine 110 of the alpha subunit of Pseudomonas stutzeri OX1 toluene-o-xylene monooxygenase influence the regiospecific oxidation of aromatics. Biotechnol Bioeng 2006; 92:652-8. [PMID: 16116657 DOI: 10.1002/bit.20637] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Saturation mutagenesis was used to generate 10 mutants of toluene-o-xylene monooxygenase (ToMO) at alpha subunit (TouA) positions A101 and A110: A101G, A101I, A101M, A101VE, A101V, A110G, A110C, A110S, A110P, and A110T; by testing the substrates toluene, o-cresol, m-cresol, p-cresol, phenol, naphthalene, o-methoxyphenol, m-methoxyphenol, p-methoxyphenol, o-xylene, and nitrobenzene, these positions were found to influence the regiospecific oxidation of aromatics. For example, compared to wild-type ToMO, TouA variant A101V produced threefold more 3-methoxycatechol from m-methoxyphenol as well as produced methylhydroquinone from o-cresol whereas wild-type ToMO did not. Similarly, variant A110C synthesized 1.8-fold more o-cresol from toluene and 1.8-fold more 3-methoxycatechol from m-methoxyphenol, and variant A110G synthesized more m-nitrophenol and twofold less p-nitrophenol from nitrobenzene. The A101V and A110C mutations did not affect the rate of reaction with the natural substrate toluene, so the variants had high activity. This is the first report that these or analogous residues influence the catalysis with this class of enzymes. Wild-type ToMO was found to oxidize o-methoxyphenol to methoxyhydroquinone (60%) and 4-methoxyresorcinol (40%), m-methoxyphenol to 4-methoxycatechol (96%) and 3-methoxycatechol (4%), and p-methoxyphenol to 4-methoxycatechol (100%).
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Affiliation(s)
- Gönül Vardar
- Department of Chemical Engineering, University of Connecticut, 191 Auditorium Road, U-3222, Storrs, Connecticut 06269, USA
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Vardar G, Wood TK. Protein engineering of toluene-o-xylene monooxygenase from Pseudomonas stutzeri OX1 for enhanced chlorinated ethene degradation and o-xylene oxidation. Appl Microbiol Biotechnol 2005; 68:510-7. [PMID: 15696279 DOI: 10.1007/s00253-005-1923-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2004] [Revised: 01/16/2005] [Accepted: 01/17/2005] [Indexed: 11/28/2022]
Abstract
Toluene-o-xylene monooxygenase (ToMO) from Pseudomonas stutzeri OX1 has been shown to degrade all chlorinated ethenes individually and as mixtures. Here, DNA shuffling of the alpha hydroxylase fragment of ToMO (TouA) and saturation mutagenesis of the TouA active site residues I100, Q141, T201, F205, and E214 were used to enhance the degradation of chlorinated aliphatics. The ToMO mutants were identified using a chloride ion screen and then were further examined by gas chromatography. Escherichia coli TG1/pBS(Kan)ToMO expressing TouA saturation mutagenesis variant I100Q was identified that has 2.8-fold better trichloroethylene (TCE) degradation activity (apparent Vmax of 1.77 nmol min-1 mg-1 protein-1 vs 0.63 nmol min-1 mg-1 protein-1). Another variant, E214G/D312N/M399V, has 2.5-fold better cis-1,2-dichloroethylene (cis-DCE) degradation activity (apparent Vmax of 8.4 nmol min-1 mg-1 protein-1 vs 3.3 nmol min-1 mg-1 protein-1). Additionally, the hydroxylation regiospecificity of o-xylene and naphthalene were altered significantly for ToMO variants A107T/E214A, T201G, and T201S. Variant T201S produced 2.0-fold more 2,3-dimethylphenol (2,3-DMP) from o-xylene than the wild-type ToMO, whereas variant A107T/E214A had 6.0-fold altered regiospecificity for 2,3-DMP formation. Variant A107T/E214A also produced 3.0-fold more 2-naphthol from naphthalene than the wild-type ToMO, whereas the regiospecificity of variant T201S was altered to synthesize 3.0-fold less 2-naphthol, so that it made almost exclusively 1-naphthol (96%). Variant T201G was more regiospecific than variants A107T/E214A and T201S and produced 100% 3,4-DMP from o-xylene and >99% 1-naphthol from naphthalene. Hence, ToMO activity was enhanced for the degradation of TCE and cis-DCE and for the regiospecific hydroxylation of o-xylene and naphthalene through DNA shuffling and saturation mutagenesis.
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Affiliation(s)
- Gönül Vardar
- Department of Chemical Engineering, University of Connecticut, 191 Auditorium Road, U-3222, Storrs, CT 06269-3222, USA
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