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Yang SNN, Haritos V, Kertesz MA, Coleman NV. A novel soluble di-iron monooxygenase from the soil bacterium Solimonas soli. Environ Microbiol 2024; 26:e16567. [PMID: 38233213 DOI: 10.1111/1462-2920.16567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2023] [Accepted: 12/12/2023] [Indexed: 01/19/2024]
Abstract
Soluble di-iron monooxygenase (SDIMO) enzymes enable insertion of oxygen into diverse substrates and play significant roles in biogeochemistry, bioremediation and biocatalysis. An unusual SDIMO was detected in an earlier study in the genome of the soil organism Solimonas soli, but was not characterized. Here, we show that the S. soli SDIMO is part of a new clade, which we define as 'Group 7'; these share a conserved gene organization with alkene monooxygenases but have only low amino acid identity. The S. soli genes (named zmoABCD) could be functionally expressed in Pseudomonas putida KT2440 but not in Escherichia coli TOP10. The recombinants made epoxides from C2 C8 alkenes, preferring small linear alkenes (e.g. propene), but also epoxidating branched, carboxylated and chlorinated substrates. Enzymatic epoxidation of acrylic acid was observed for the first time. ZmoABCD oxidised the organochlorine pollutants vinyl chloride (VC) and cis-1,2-dichloroethene (cDCE), with the release of inorganic chloride from VC but not cDCE. The original host bacterium S. soli could not grow on any alkenes tested but grew well on phenol and n-octane. Further work is needed to link ZmoABCD and the other Group 7 SDIMOs to specific physiological and ecological roles.
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Affiliation(s)
- Sui Nin Nicholas Yang
- School of Life and Environmental Sciences, University of Sydney, Camperdown, New South Wales, Australia
| | - Victoria Haritos
- Department of Chemical and Biological Engineering, Monash University, Melbourne, Victoria, Australia
| | - Michael A Kertesz
- School of Life and Environmental Sciences, University of Sydney, Camperdown, New South Wales, Australia
| | - Nicholas V Coleman
- School of Life and Environmental Sciences, University of Sydney, Camperdown, New South Wales, Australia
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2
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Chen Y, Ren H, Kong X, Wu H, Lu Z. A multicomponent propane monooxygenase catalyzes the initial degradation of methyl tert-butyl ether in Mycobacterium vaccae JOB5. Appl Environ Microbiol 2023; 89:e0118723. [PMID: 37823642 PMCID: PMC10617536 DOI: 10.1128/aem.01187-23] [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: 07/10/2023] [Accepted: 08/30/2023] [Indexed: 10/13/2023] Open
Abstract
Methyl tert-butyl ether (MTBE) has been recognized as a groundwater contaminant due to its widespread distribution and potential threat to human health. The limited understanding of the enzymes catalyzing MTBE degradation restricts their application in MTBE bioremediation. In this study, an MTBE-degrading soluble di-iron monooxygenase that clusters phylogenetically with a known propane monooxygenase (PRM) encoded by the prmABCD gene cluster was identified and functionally characterized, revealing their role in MTBE metabolism by Mycobacterium vaccae JOB5. Transcriptome analysis demonstrated that the expression of prmABCD was upregulated when JOB5 was induced by MTBE. Escherichia coli Rosetta heterologously expressing prmABCD from JOB5 could transform MTBE, indicating that the PRM of JOB5 is capable of the initial degradation of MTBE. The loss of the gene encoding the oxygenase α-subunit or β-subunit, the coupling protein, or the reductase disrupted MTBE transformation by the recombinant E. coli Rosetta. In addition, the catalytic capacity of PRM is likely affected by residue G95 in the active site pocket and residues I84, P165, A269, and V270 in the substrate tunnel structure. Mutation of amino acids in the active site and substrate tunnel resulted in inefficiency or inactivation of MTBE degradation, and the activity in 1,4-dioxane (1,4-D) degradation was diminished less than that in MTBE degradation.IMPORTANCEMulticomponent monooxygenases catalyzing the initial hydroxylation of MTBE are important in MTBE biodegradation. Previous studies of MTBE degradation enzymes have focused on P450s, alkane monooxygenase and MTBE monooxygenase, but the vital role of soluble di-iron monooxygenases has rarely been reported. In this study, we deciphered the essential catalytic role of a PRM and revealed the key residues of the PRM in MTBE metabolism. Our findings provide new insight into the MTBE-degrading gene cluster and enzymes in bacteria. This characterization of the PRM associated with MTBE degradation expands our understanding of MTBE-degrading gene diversity and provides a novel candidate enzyme for the bioremediation of MTBE-contaminated sites.
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Affiliation(s)
- Yiyang Chen
- MOE Laboratory of Biosystem Homeostasis and Protection, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
- Cancer Center, Zhejiang University, Hangzhou, Zhejiang, China
| | - Hao Ren
- MOE Laboratory of Biosystem Homeostasis and Protection, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
- Cancer Center, Zhejiang University, Hangzhou, Zhejiang, China
| | - Xiangyu Kong
- MOE Laboratory of Biosystem Homeostasis and Protection, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
- Cancer Center, Zhejiang University, Hangzhou, Zhejiang, China
| | - Hao Wu
- MOE Laboratory of Biosystem Homeostasis and Protection, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
- Cancer Center, Zhejiang University, Hangzhou, Zhejiang, China
| | - Zhenmei Lu
- MOE Laboratory of Biosystem Homeostasis and Protection, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, China
- Cancer Center, Zhejiang University, Hangzhou, Zhejiang, China
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3
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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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4
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Jones JC, Banerjee R, Semonis MM, Shi K, Aihara H, Lipscomb JD. X-ray Crystal Structures of Methane Monooxygenase Hydroxylase Complexes with Variants of Its Regulatory Component: Correlations with Altered Reaction Cycle Dynamics. Biochemistry 2022; 61:21-33. [PMID: 34910460 PMCID: PMC8727504 DOI: 10.1021/acs.biochem.1c00673] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Full activity of soluble methane monooxygenase (sMMO) depends upon the formation of a 1:1 complex of the regulatory protein MMOB with each alpha subunit of the (αβγ)2 hydroxylase, sMMOH. Previous studies have shown that mutations in the core region of MMOB and in the N- and C-termini cause dramatic changes in the rate constants for steps in the sMMOH reaction cycle. Here, X-ray crystal structures are reported for the sMMOH complex with two double variants within the core region of MMOB, DBL1 (N107G/S110A), and DBL2 (S109A/T111A), as well as two variants in the MMOB N-terminal region, H33A and H5A. DBL1 causes a 150-fold decrease in the formation rate constant of the reaction cycle intermediate P, whereas DBL2 accelerates the reaction of the dinuclear Fe(IV) intermediate Q with substrates larger than methane by three- to fourfold. H33A also greatly slows P formation, while H5A modestly slows both formation of Q and its reactions with substrates. Complexation with DBL1 or H33A alters the position of sMMOH residue R245, which is part of a conserved hydrogen-bonding network encompassing the active site diiron cluster where P is formed. Accordingly, electron paramagnetic resonance spectra of sMMOH:DBL1 and sMMOH:H33A complexes differ markedly from that of sMMOH:MMOB, showing an altered electronic environment. In the sMMOH:DBL2 complex, the position of M247 in sMMOH is altered such that it enlarges a molecular tunnel associated with substrate entry into the active site. The H5A variant causes only subtle structural changes despite its kinetic effects, emphasizing the precise alignment of sMMOH and MMOB required for efficient catalysis.
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Affiliation(s)
- Jason C. Jones
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, U. S. A.,Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, U. S. A
| | - Rahul Banerjee
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, U. S. A.,Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, U. S. A
| | - Manny M. Semonis
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, U. S. A.,Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, U. S. A
| | - Ke Shi
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, U. S. A
| | - Hideki Aihara
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, U. S. A
| | - John D. Lipscomb
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, U. S. A.,Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, U. S. A.,Corresponding Author:
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5
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Banerjee R, Srinivas V, Lebrette H. Ferritin-Like Proteins: A Conserved Core for a Myriad of Enzyme Complexes. Subcell Biochem 2022; 99:109-153. [PMID: 36151375 DOI: 10.1007/978-3-031-00793-4_4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Ferritin-like proteins share a common fold, a four α-helix bundle core, often coordinating a pair of metal ions. Although conserved, the ferritin fold permits a diverse set of reactions, and is central in a multitude of macromolecular enzyme complexes. Here, we emphasize this diversity through three members of the ferritin-like superfamily: the soluble methane monooxygenase, the class I ribonucleotide reductase and the aldehyde deformylating oxygenase. They all rely on dinuclear metal cofactors to catalyze different challenging oxygen-dependent reactions through the formation of multi-protein complexes. Recent studies using cryo-electron microscopy, serial femtosecond crystallography at an X-ray free electron laser source, or single-crystal X-ray diffraction, have reported the structures of the active protein complexes, and revealed unprecedented insights into the molecular mechanisms of these three enzymes.
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Affiliation(s)
- Rahul Banerjee
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN, USA
| | - Vivek Srinivas
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | - Hugo Lebrette
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden.
- Laboratoire de Microbiologie et Génétique Moléculaires (LMGM), Centre de Biologie Intégrative (CBI), CNRS, UPS, Université de Toulouse, Toulouse, France.
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6
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Lee C, Ha SC, Rao Z, Hwang Y, Kim DS, Kim SY, Yoo H, Yoon C, Na JG, Park JH, Lee SJ. Elucidation of the electron transfer environment in the MMOR FAD-binding domain from Methylosinus sporium 5. Dalton Trans 2021; 50:16493-16498. [PMID: 34734616 DOI: 10.1039/d1dt03273a] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
By facilitating electron transfer to the hydroxylase diiron center, MMOR-a reductase-serves as an essential component of the catalytic cycle of soluble methane monooxygenase. Here, the X-ray structure analysis of the FAD-binding domain of MMOR identified crucial residues and its influence on the catalytic cycle.
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Affiliation(s)
- Chaemin Lee
- Department of Chemistry and Institute of Molecular Biology and Genetics, Jeonbuk National University, Jeonju 54796, Republic of Korea.
| | - Sung Chul Ha
- Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
| | - Zhili Rao
- Division of Biotechnology, College of Environmental & Bioresources Sciences, Jeonbuk National University, Iksan 54596, Republic of Korea.
| | - Yunha Hwang
- Department of Chemistry and Institute of Molecular Biology and Genetics, Jeonbuk National University, Jeonju 54796, Republic of Korea.
| | - Da Som Kim
- Division of Biotechnology, College of Environmental & Bioresources Sciences, Jeonbuk National University, Iksan 54596, Republic of Korea.
| | - So Young Kim
- Division of Biotechnology, College of Environmental & Bioresources Sciences, Jeonbuk National University, Iksan 54596, Republic of Korea.
| | - Heeseon Yoo
- Department of Chemistry and Institute of Molecular Biology and Genetics, Jeonbuk National University, Jeonju 54796, Republic of Korea.
| | - Chungwoon Yoon
- Department of Chemistry and Institute of Molecular Biology and Genetics, Jeonbuk National University, Jeonju 54796, Republic of Korea.
| | - Jeong-Geol Na
- Department of Chemical and Biomolecular Engineering, Sogang University, Seoul 04107, Republic of Korea.
| | - Jung Hee Park
- Division of Biotechnology, College of Environmental & Bioresources Sciences, Jeonbuk National University, Iksan 54596, Republic of Korea. .,Advanced Institute of Environment and Bioscience, College of Environmental & Bioresources Sciences, Jeonbuk National University, Iksan 54596, Republic of Korea
| | - Seung Jae Lee
- Department of Chemistry and Institute of Molecular Biology and Genetics, Jeonbuk National University, Jeonju 54796, Republic of Korea.
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7
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Banerjee R, Lipscomb JD. Small-Molecule Tunnels in Metalloenzymes Viewed as Extensions of the Active Site. Acc Chem Res 2021; 54:2185-2195. [PMID: 33886257 DOI: 10.1021/acs.accounts.1c00058] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Rigorous substrate selectivity is a hallmark of enzyme catalysis. This selectivity is generally ascribed to a thermodynamically favorable process of substrate binding to the enzyme active site based upon complementary physiochemical characteristics, which allows both acquisition and orientation. However, this chemical selectivity is more difficult to rationalize for diminutive molecules that possess too narrow a range of physical characteristics to allow either precise positioning or discrimination between a substrate and an inhibitor. Foremost among these small molecules are dissolved gases such as H2, N2, O2, CO, CO2, NO, N2O, NH3, and CH4 so often encountered in metalloenzyme catalysis. Nevertheless, metalloenzymes have evolved to metabolize these small-molecule substrates with high selectivity and efficiency.The soluble methane monooxygenase enzyme (sMMO) acts upon two of these small molecules, O2 and CH4, to generate methanol as part of the C1 metabolic pathway of methanotrophic organisms. sMMO is capable of oxidizing many alternative hydrocarbon substrates. Remarkably, however, it will preferentially oxidize methane, the substrate with the fewest discriminating physical characteristics and the strongest C-H bond. Early studies led us to broadly attribute this specificity to the formation of a "molecular sieve" in which a methane- and oxygen-sized tunnel provides a size-selective route from bulk solvent to the completely buried sMMO active site. Indeed, recent cryogenic and serial femtosecond ambient temperature crystallographic studies have revealed such a route in sMMO. A detailed study of the sMMO tunnel considered here in the context of small-molecule tunnels identified in other metalloenzymes reveals three discrete characteristics that contribute to substrate selectivity and positioning beyond that which can be provided by the active site itself. Moreover, the dynamic nature of many tunnels allows an exquisite coordination of substrate binding and reaction phases of the catalytic cycle. Here we differentiate between the highly selective molecular tunnel, which allows only the one-dimensional transit of small molecules, and the larger, less-selective channels found in typical enzymes. Methods are described to identify and characterize tunnels as well as to differentiate them from channels. In metalloenzymes which metabolize dissolved gases, we posit that the contribution of tunnels is so great that they should be considered to be extensions of the active site itself. A full understanding of catalysis by these enzymes requires an appreciation of the roles played by tunnels. Such an understanding will also facilitate the use of the enzymes or their synthetic mimics in industrial or pharmaceutical applications.
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Affiliation(s)
- Rahul Banerjee
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55391, United States
| | - John D. Lipscomb
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55391, United States
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8
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Du K, Zemerov SD, Carroll PJ, Dmochowski IJ. Paramagnetic Shifts and Guest Exchange Kinetics in Co nFe 4-n Metal-Organic Capsules. Inorg Chem 2020; 59:12758-12767. [PMID: 32851844 DOI: 10.1021/acs.inorgchem.0c01816] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We investigate the magnetic resonance properties and exchange kinetics of guest molecules in a series of hetero-bimetallic capsules, [ConFe4-nL6]4- (n = 1-3), where L2- = 4,4'-bis[(2-pyridinylmethylene)amino]-[1,1'-biphenyl]-2,2'-disulfonate. H bond networks between capsule sulfonates and guanidinium cations promote the crystallization of [ConFe4-nL6]4-. The following four isostructural crystals are reported: two guest-free forms, (C(NH2)3)4[Co1.8Fe2.2L6]·69H2O (1) and (C(NH2)3)4[Co2.7Fe1.3L6]·73H2O (2), and two Xe- and CFCl3-encapsulated forms, (C(NH2)3)4[(Xe)0.8Co1.8Fe2.2L6]·69H2O (3) and (C(NH2)3)4[(CFCl3)Co2.0Fe2.0L6]·73H2O (4), respectively. Structural analyses reveal that Xe induces negligible structural changes in 3, while the angles between neighboring phenyl groups expand by ca. 3° to accommodate the much larger guest, CFCl3, in 4. These guest-encapsulated [ConFe4-nL6]4- molecules reveal 129Xe and 19F chemical shift changes of ca. -22 and -10 ppm at 298 K, respectively, per substitution of low-spin FeII by high-spin CoII. Likewise, the temperature dependence of the 129Xe and 19F NMR resonances increases by 0.1 and 0.06 ppm/K, respectively, with each additional paramagnetic CoII center. The optimal temperature for hyperpolarized (hp) 129Xe chemical exchange saturation transfer (hyper-CEST) with [ConFe4-nL6]4- capsules was found to be inversely proportional to the number of CoII centers, n, which is consistent with the Xe chemical exchange accelerating as the portals expand. The systematic study was facilitated by the tunability of the [M4L6]4- capsules, further highlighting these metal-organic systems for developing responsive sensors with highly shifted 129Xe resonances.
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Affiliation(s)
- Kang Du
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
| | - Serge D Zemerov
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
| | - Patrick J Carroll
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
| | - Ivan J Dmochowski
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
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9
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Srinivas V, Banerjee R, Lebrette H, Jones JC, Aurelius O, Kim IS, Pham CC, Gul S, Sutherlin KD, Bhowmick A, John J, Bozkurt E, Fransson T, Aller P, Butryn A, Bogacz I, Simon P, Keable S, Britz A, Tono K, Kim KS, Park SY, Lee SJ, Park J, Alonso-Mori R, Fuller FD, Batyuk A, Brewster AS, Bergmann U, Sauter NK, Orville AM, Yachandra VK, Yano J, Lipscomb JD, Kern J, Högbom M. High-Resolution XFEL Structure of the Soluble Methane Monooxygenase Hydroxylase Complex with its Regulatory Component at Ambient Temperature in Two Oxidation States. J Am Chem Soc 2020; 142:14249-14266. [PMID: 32683863 PMCID: PMC7457426 DOI: 10.1021/jacs.0c05613] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Soluble methane monooxygenase (sMMO) is a multicomponent metalloenzyme that catalyzes the conversion of methane to methanol at ambient temperature using a nonheme, oxygen-bridged dinuclear iron cluster in the active site. Structural changes in the hydroxylase component (sMMOH) containing the diiron cluster caused by complex formation with a regulatory component (MMOB) and by iron reduction are important for the regulation of O2 activation and substrate hydroxylation. Structural studies of metalloenzymes using traditional synchrotron-based X-ray crystallography are often complicated by partial X-ray-induced photoreduction of the metal center, thereby obviating determination of the structure of the enzyme in pure oxidation states. Here, microcrystals of the sMMOH:MMOB complex from Methylosinus trichosporium OB3b were serially exposed to X-ray free electron laser (XFEL) pulses, where the ≤35 fs duration of exposure of an individual crystal yields diffraction data before photoreduction-induced structural changes can manifest. Merging diffraction patterns obtained from thousands of crystals generates radiation damage-free, 1.95 Å resolution crystal structures for the fully oxidized and fully reduced states of the sMMOH:MMOB complex for the first time. The results provide new insight into the manner by which the diiron cluster and the active site environment are reorganized by the regulatory protein component in order to enhance the steps of oxygen activation and methane oxidation. This study also emphasizes the value of XFEL and serial femtosecond crystallography (SFX) methods for investigating the structures of metalloenzymes with radiation sensitive metal active sites.
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Affiliation(s)
- Vivek Srinivas
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
| | - Rahul Banerjee
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55391 U.S.A
| | - Hugo Lebrette
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
| | - Jason C. Jones
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55391 U.S.A
| | - Oskar Aurelius
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
| | - In-Sik Kim
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 U.S.A
| | - Cindy C. Pham
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 U.S.A
| | - Sheraz Gul
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 U.S.A
| | - Kyle D. Sutherlin
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 U.S.A
| | - Asmit Bhowmick
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 U.S.A
| | - Juliane John
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
| | - Esra Bozkurt
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
| | - Thomas Fransson
- Interdisciplinary Center for Scientific Computing, University of Heidelberg, 69120 Heidelberg, Germany
| | - Pierre Aller
- Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, UK
| | - Agata Butryn
- Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, UK
| | - Isabel Bogacz
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 U.S.A
| | - Philipp Simon
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 U.S.A
| | - Stephen Keable
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 U.S.A
| | - Alexander Britz
- LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025 U.S.A
| | - Kensuke Tono
- Japan Synchrotron Radiation Research Institute, Sayo-gun 679 5198, Japan
| | - Kyung Sook Kim
- Pohang Accelerator Laboratory, Gyeongsangbuk-do 37673, South Korea
| | - Sang-Youn Park
- Pohang Accelerator Laboratory, Gyeongsangbuk-do 37673, South Korea
| | - Sang Jae Lee
- Pohang Accelerator Laboratory, Gyeongsangbuk-do 37673, South Korea
| | - Jaehyun Park
- Pohang Accelerator Laboratory, Gyeongsangbuk-do 37673, South Korea
| | - Roberto Alonso-Mori
- LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025 U.S.A
| | - Franklin D. Fuller
- LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025 U.S.A
| | - Alexander Batyuk
- LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025 U.S.A
| | - Aaron S. Brewster
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 U.S.A
| | - Uwe Bergmann
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California, 94025 U.S.A
| | - Nicholas K. Sauter
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 U.S.A
| | - Allen M. Orville
- Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, UK
- Research Complex at Harwell, Rutherford Appleton Laboratory, Didcot, Oxfordshire, OX11 0FA, UK
| | - Vittal K. Yachandra
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 U.S.A
| | - Junko Yano
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 U.S.A
| | - John D. Lipscomb
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55391 U.S.A
| | - Jan Kern
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 U.S.A
| | - Martin Högbom
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Stockholm, Sweden
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10
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Jones JC, Banerjee R, Shi K, Aihara H, Lipscomb JD. Structural Studies of the Methylosinus trichosporium OB3b Soluble Methane Monooxygenase Hydroxylase and Regulatory Component Complex Reveal a Transient Substrate Tunnel. Biochemistry 2020; 59:2946-2961. [PMID: 32692178 PMCID: PMC7457393 DOI: 10.1021/acs.biochem.0c00459] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The metalloenzyme soluble methane monooxygenase (sMMO) consists of hydroxylase (sMMOH), regulatory (MMOB), and reductase components. When sMMOH forms a complex with MMOB, the rate constants are greatly increased for the sequential access of O2, protons, and CH4 to an oxygen-bridged diferrous metal cluster located in the buried active site. Here, we report high-resolution X-ray crystal structures of the diferric and diferrous states of both sMMOH and the sMMOH:MMOB complex using the components from Methylosinus trichosporium OB3b. These structures are analyzed for O2 access routes enhanced when the complex forms. Previously reported, lower-resolution structures of the sMMOH:MMOB complex from the sMMO of Methylococcus capsulatus Bath revealed a series of cavities through sMMOH postulated to serve as the O2 conduit. This potential role is evaluated in greater detail using the current structures. Additionally, a search for other potential O2 conduits in the M. trichosporium OB3b sMMOH:MMOB complex revealed a narrow molecular tunnel, termed the W308-tunnel. This tunnel is sized appropriately for O2 and traverses the sMMOH-MMOB interface before accessing the active site. The kinetics of reaction of O2 with the diferrous sMMOH:MMOB complex in solution show that use of the MMOB V41R variant decreases the rate constant for O2 binding >25000-fold without altering the component affinity. The location of Val41 near the entrance to the W308-tunnel is consistent with the tunnel serving as the primary route for the transfer of O2 into the active site. Accordingly, the crystal structures show that formation of the diferrous sMMOH:MMOB complex restricts access through the chain of cavities while opening the W308-tunnel.
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Affiliation(s)
- Jason C. Jones
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, United States
- Center for Metals in Biocatalysis University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Rahul Banerjee
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, United States
- Center for Metals in Biocatalysis University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Ke Shi
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Hideki Aihara
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - John D. Lipscomb
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, United States
- Center for Metals in Biocatalysis University of Minnesota, Minneapolis, Minnesota 55455, United States
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11
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Osborne CD, Haritos VS. Beneath the surface: Evolution of methane activity in the bacterial multicomponent monooxygenases. Mol Phylogenet Evol 2019; 139:106527. [PMID: 31173882 DOI: 10.1016/j.ympev.2019.106527] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 06/03/2019] [Accepted: 06/03/2019] [Indexed: 02/09/2023]
Abstract
The bacterial multicomponent monooxygenase (BMM) family has evolved to oxidise a wide array of hydrocarbon substrates of importance to environmental emissions and biotechnology: foremost amongst these is methane, which requires among the most powerful oxidant in biology to activate. To understand how the BMM evolved methane oxidation activity, we investigated the changes in the enzyme family at different levels: operonic, phylogenetic analysis of the catalytic hydroxylase, subunit or folding factor presence, and sequence-function analysis across the entirety of the BMM phylogeny. Our results show that the BMM evolution of new activities was enabled by incremental increases in oxidative power of the active site, and these occur in multiple branches of the hydroxylase phylogenetic tree. While the hydroxylase primary sequence changes that resulted in increased oxidative power of the enzyme appear to be minor, the principle evolutionary advances enabling methane activity occurred in the other components of the BMM complex and in the recruitment of stability proteins. We propose that enzyme assembly and stabilization factors have independently-evolved multiple times in the BMM family to support enzymes that oxidise increasingly difficult substrates. Herein, we show an important example of evolution of catalytic function where modifications to the active site and substrate accessibility, which are the usual focus of enzyme evolution, are overshadowed by broader scale changes to structural stabilization and non-catalytic unit development. Retracing macroscale changes during enzyme evolution, as demonstrated here, should find ready application to other enzyme systems and in protein design.
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Affiliation(s)
- Craig D Osborne
- Department of Chemical Engineering, Monash University, Wellington Road, Clayton 3800, Australia
| | - Victoria S Haritos
- Department of Chemical Engineering, Monash University, Wellington Road, Clayton 3800, Australia.
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12
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13
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Biocatalytic Oxidations of Substrates through Soluble Methane Monooxygenase from Methylosinus sporium 5. Catalysts 2018. [DOI: 10.3390/catal8120582] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Methane, an important greenhouse gas, has a 20-fold higher heat capacity than carbon dioxide. Earlier, through advanced spectroscopy and structural studies, the mechanisms underlying the extremely stable C–H activation of soluble methane monooxygenase (sMMO) have been elucidated in Methylosinus trichosporium OB3b and Methylococcus capsulatus Bath. Here, sMMO components—including hydroxylase (MMOH), regulatory (MMOB), and reductase (MMOR)—were expressed and purified from a type II methanotroph, Methylosinus sporium strain 5 (M. sporium 5), to characterize its hydroxylation mechanism. Two molar equivalents of MMOB are necessary to achieve catalytic activities and oxidized a broad range of substrates including alkanes, alkenes, halogens, and aromatics. Optimal activities were observed at pH 7.5 for most substrates possibly because of the electron transfer environment in MMOR. Substitution of MMOB or MMOR from another type II methanotroph, Methylocystis species M, retained specific enzyme activities, demonstrating the successful cross-reactivity of M. sporium 5. These results will provide fundamental information for further enzymatic studies to elucidate sMMO mechanisms.
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14
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Wang J, Shen X, Wang J, Yang Y, Yuan Q, Yan Y. Exploring the Promiscuity of Phenol Hydroxylase from Pseudomonas stutzeri OX1 for the Biosynthesis of Phenolic Compounds. ACS Synth Biol 2018; 7:1238-1243. [PMID: 29659242 DOI: 10.1021/acssynbio.8b00067] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Enzyme promiscuity plays an important role in developing biosynthetic pathways for novel target products. Phenol hydroxylase (PH) from Pseudomonas stutzeri OX1 is capable of ortho-hydroxylation of phenol and cresol isomers into counterpart catechols. A small ferredoxin-like protein PHQ was clustered together with the ph gene cluster in the genome of P. stutzeri OX1, and its function was not known. In this study, we found that the existence of PHQ has a promotion effect on the catalytic efficiency of PH. Then, we tested the substrate range of PH using nine different non-natural substrates. We found that PH was a promiscuous hydroxylase that could catalyze ortho-hydroxylation of several non-natural substrates, including catechol, 4-hydroxybenzoic acid and resorcinol. On this basis, linking the catechol biosynthetic pathway with the hydroxylation reaction catalyzed by PH enabled construction of a novel biosynthetic pathway for the synthesis of pyrogallol. This work not only characterized a well-performed PH, but also provided a promising hydroxylation platform for the production of high-value phenolic compounds.
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Affiliation(s)
- Jia Wang
- Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China
- State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China
| | - Xiaolin Shen
- Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China
- State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China
| | - Jian Wang
- School of Chemical, Materials and Biomedical Engineering, College of Engineering, The University of Georgia, Athens, Georgia 30602, United States
| | - Yaping Yang
- School of Chemical, Materials and Biomedical Engineering, College of Engineering, The University of Georgia, Athens, Georgia 30602, United States
| | - Qipeng Yuan
- Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China
- State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China
| | - Yajun Yan
- School of Chemical, Materials and Biomedical Engineering, College of Engineering, The University of Georgia, Athens, Georgia 30602, United States
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15
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Rokob TA. Pathways for Arene Oxidation in Non-Heme Diiron Enzymes: Lessons from Computational Studies on Benzoyl Coenzyme A Epoxidase. J Am Chem Soc 2016; 138:14623-14638. [PMID: 27682344 DOI: 10.1021/jacs.6b06987] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Oxygenation of aromatic rings using O2 is catalyzed by several non-heme carboxylate-bridged diiron enzymes. In order to provide a general mechanistic description for these reactions, computational studies were carried out at the ONIOM(B3LYP/BP86/Amber) level on the non-heme diiron enzyme benzoyl coenzyme A epoxidase, BoxB. The calculations revealed four possible pathways for attacking the aromatic ring: (a) electrophilic (2e-) attack by a bis(μ-oxo)-diiron(IV) species (Q pathway); (b) electrophilic (2e-) attack via the σ* orbital of a μ-η2:η2-peroxo-diiron(III) intermediate (Pσ* pathway); (c) radical (1e-) attack via the π*-orbital of a superoxo-diiron(II,III) species (Pπ* pathway); (d) radical (1e-) attack of a partially quenched bis(μ-oxo)-diiron(IV) intermediate (Q' pathway). The results allowed earlier work of de Visser on olefin epoxidation by diiron complexes and QM-cluster studies of Liao and Siegbahn on BoxB to be put into a broader perspective. Parallels with epoxidation using organic peracids were also examined. Specifically for the BoxB enzyme, the Q pathway was found to be the most preferred, but the corresponding bis(μ-oxo)-diiron(IV) species is significantly destabilized and not expected to be directly observable. Epoxidation via the Pσ* pathway represents an energetically somewhat higher lying alternative; possible strategies for experimental discrimination are discussed. The selectivity toward epoxidation is shown to stem from a combination of inherent electronic properties of the thioacyl substituent and enzymatic constraints. Possible implications of the results for toluene monooxygenases are considered as well.
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Affiliation(s)
- Tibor András Rokob
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences , Magyar Tudósok körútja 2, 1117 Budapest, Hungary
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16
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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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17
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Lee SJ. Hydroxylation of methane through component interactions in soluble methane monooxygenases. J Microbiol 2016; 54:277-82. [DOI: 10.1007/s12275-016-5642-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2015] [Revised: 02/25/2016] [Accepted: 02/26/2016] [Indexed: 10/22/2022]
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18
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Mahinthichaichan P, Gennis RB, Tajkhorshid E. All the O2 Consumed by Thermus thermophilus Cytochrome ba3 Is Delivered to the Active Site through a Long, Open Hydrophobic Tunnel with Entrances within the Lipid Bilayer. Biochemistry 2016; 55:1265-78. [PMID: 26845082 DOI: 10.1021/acs.biochem.5b01255] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Cytochrome ba3 is a proton-pumping heme-copper oxygen reductase from the extreme thermophile Thermus thermophilus. Despite the fact that the enzyme's active site is buried deep within the protein, the apparent second order rate constant for the initial binding of O2 to the active-site heme has been experimentally found to be 10(9) M(-1) s(-1) at 298 K, at or near the diffusion limit, and 2 orders of magnitude faster than for O2 binding to myoglobin. To provide quantitative and microscopic descriptions of the O2 delivery pathway and mechanism in cytochrome ba3, extensive molecular dynamics simulations of the enzyme in its membrane-embedded form have been performed, including different protocols of explicit ligand sampling (flooding) simulations with O2, implicit ligand sampling analysis, and in silico mutagenesis. The results show that O2 diffuses to the active site exclusively via a Y-shaped hydrophobic tunnel with two 25-Å long membrane-accessible branches that coincide with the pathway previously suggested by the crystallographically identified xenon binding sites. The two entrances of the bifurcated tunnel of cytochrome ba3 are located within the lipid bilayer, where O2 is preferentially partitioned from the aqueous phase. The largest barrier to O2 migration within the tunnel is estimated to be only 1.5 kcal/mol, allowing O2 to reach the enzyme active site virtually impeded by one-dimensional diffusion once it reaches a tunnel entrance at the protein surface. Unlike other O2-utilizing proteins, the tunnel is "open" with no transient barriers observed due to protein dynamics. This unique low-barrier passage through the protein ensures that O2 transit through the protein is never rate-limiting.
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Affiliation(s)
- Paween Mahinthichaichan
- Department of Biochemistry, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Robert B Gennis
- Department of Biochemistry, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Emad Tajkhorshid
- Department of Biochemistry, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
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19
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Wang W, Liang AD, Lippard SJ. Coupling Oxygen Consumption with Hydrocarbon Oxidation in Bacterial Multicomponent Monooxygenases. Acc Chem Res 2015; 48:2632-9. [PMID: 26293615 PMCID: PMC4624108 DOI: 10.1021/acs.accounts.5b00312] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
A fundamental goal in catalysis is the coupling of multiple reactions to yield a desired product. Enzymes have evolved elegant approaches to address this grand challenge. A salient example is the biological conversion of methane to methanol catalyzed by soluble methane monooxygenase (sMMO), a member of the bacterial multicomponent monooxygenase (BMM) superfamily. sMMO is a dynamic protein complex of three components: a hydroxylase, a reductase, and a regulatory protein. The active site, a carboxylate-rich non-heme diiron center, is buried inside the 251 kDa hydroxylase component. The enzyme processes four substrates: O2, protons, electrons, and methane. To couple O2 activation to methane oxidation, timely control of substrate access to the active site is critical. Recent studies of sMMO, as well as its homologues in the BMM superfamily, have begun to unravel the mechanism. The emerging and unifying picture reveals that each substrate gains access to the active site along a specific pathway through the hydroxylase. Electrons and protons are delivered via a three-amino-acid pore located adjacent to the diiron center; O2 migrates via a series of hydrophobic cavities; and hydrocarbon substrates reach the active site through a channel or linked set of cavities. The gating of these pathways mediates entry of each substrate to the diiron active site in a timed sequence and is coordinated by dynamic interactions with the other component proteins. The result is coupling of dioxygen consumption with hydrocarbon oxidation, avoiding unproductive oxidation of the reductant rather than the desired hydrocarbon. To initiate catalysis, the reductase delivers two electrons to the diiron(III) center by binding over the pore of the hydroxylase. The regulatory component then displaces the reductase, docking onto the same surface of the hydroxylase. Formation of the hydroxylase-regulatory component complex (i) induces conformational changes of pore residues that may bring protons to the active site; (ii) connects hydrophobic cavities in the hydroxylase leading from the exterior to the diiron active site, providing a pathway for O2 and methane, in the case of sMMO, to the reduced diiron center for O2 activation and substrate hydroxylation; (iii) closes the pore, as well as a channel in the case of four-component BMM enzymes, restricting proton access to the diiron center during formation of "Fe2O2" intermediates required for hydrocarbon oxidation; and (iv) inhibits undesired electron transfer to the Fe2O2 intermediates by blocking reductase binding during O2 activation. This mechanism is quite different from that adopted by cytochromes P450, a large class of heme-containing monooxygenases that catalyze reactions very similar to those catalyzed by the BMM enzymes. Understanding the timed enzyme control of substrate access has implications for designing artificial catalysts. To achieve multiple turnovers and tight coupling, synthetic models must also control substrate access, a major challenge considering that nature requires large, multimeric, dynamic protein complexes to accomplish this feat.
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Affiliation(s)
- Weixue Wang
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Alexandria D. Liang
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Stephen J. Lippard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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20
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Han Z, Sakai N, Böttger LH, Klinke S, Hauber J, Trautwein AX, Hilgenfeld R. Crystal Structure of the Peroxo-diiron(III) Intermediate of Deoxyhypusine Hydroxylase, an Oxygenase Involved in Hypusination. Structure 2015; 23:882-892. [PMID: 25865244 DOI: 10.1016/j.str.2015.03.002] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Revised: 03/09/2015] [Accepted: 03/10/2015] [Indexed: 10/23/2022]
Abstract
Deoxyhypusine hydroxylase (DOHH) is a non-heme diiron enzyme involved in the posttranslational modification of a critical lysine residue of eukaryotic translation initiation factor 5A (eIF-5A) to yield the unusual amino acid residue hypusine. This modification is essential for the role of eIF-5A in translation and in nuclear export of a group of specific mRNAs. The diiron center of human DOHH (hDOHH) forms a peroxo-diiron(III) intermediate (hDOHHperoxo) when its reduced form reacts with O2. hDOHHperoxo has a lifetime exceeding that of the peroxo intermediates of other diiron enzymes by several orders of magnitude. Here we report the 1.7-Å crystal structures of hDOHHperoxo and a complex with glycerol. The structure of hDOHHperoxo reveals the presence of a μ-1,2-peroxo-diiron(III) species at the active site. Augmented by UV/Vis and Mössbauer spectroscopic studies, the crystal structures offer explanations for the extreme longevity of hDOHHperoxo and illustrate how the enzyme specifically recognizes its only substrate, deoxyhypusine-eIF-5A.
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Affiliation(s)
- Zhenggang Han
- Institute of Biochemistry, Center for Structural and Cell Biology in Medicine, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany
| | - Naoki Sakai
- Institute of Biochemistry, Center for Structural and Cell Biology in Medicine, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany
| | - Lars H Böttger
- Institute of Physics, Center for Structural and Cell Biology in Medicine, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany
| | - Sebastián Klinke
- Institute of Biochemistry, Center for Structural and Cell Biology in Medicine, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany
| | - Joachim Hauber
- Heinrich Pette Institute - Leibniz Institute for Experimental Virology, Martinistraße 52, 20251 Hamburg, Germany; German Center for Infection Research (DZIF) c/o Heinrich-Pette-Institute - Leibniz Institute for Experimental Virology, Martinistraße 52, 20251 Hamburg, Germany
| | - Alfred X Trautwein
- Institute of Physics, Center for Structural and Cell Biology in Medicine, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany
| | - Rolf Hilgenfeld
- Institute of Biochemistry, Center for Structural and Cell Biology in Medicine, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany; German Center for Infection Research (DZIF) c/o Institute of Biochemistry, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany.
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21
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Morrison CN, Hoy JA, Zhang L, Einsle O, Rees DC. Substrate pathways in the nitrogenase MoFe protein by experimental identification of small molecule binding sites. Biochemistry 2015; 54:2052-60. [PMID: 25710326 PMCID: PMC4590346 DOI: 10.1021/bi501313k] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
![]()
In
the nitrogenase molybdenum-iron (MoFe) protein, we have identified
five potential substrate access pathways from the protein surface
to the FeMo-cofactor (the active site) or the P-cluster using experimental
structures of Xe pressurized into MoFe protein crystals from Azotobacter vinelandii and Clostridium pasteurianum. Additionally, all published structures of the MoFe protein, including
those from Klebsiella pneumoniae, were analyzed for
the presence of nonwater, small molecules bound to the protein interior.
Each pathway is based on identification of plausible routes from buried
small molecule binding sites to both the protein surface and a metallocluster.
Of these five pathways, two have been previously suggested as substrate
access pathways. While the small molecule binding sites are not conserved
among the three species of MoFe protein, residues lining the pathways
are generally conserved, indicating that the proposed pathways may
be accessible in all three species. These observations imply that
there is unlikely a unique pathway utilized for substrate access from
the protein surface to the active site; however, there may be preferred
pathways such as those described here.
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Affiliation(s)
- Christine N Morrison
- †Division of Chemistry and Chemical Engineering, California Institute of Technology 114-96, Pasadena, California 91125, United States
| | - Julie A Hoy
- †Division of Chemistry and Chemical Engineering, California Institute of Technology 114-96, Pasadena, California 91125, United States
| | - Limei Zhang
- †Division of Chemistry and Chemical Engineering, California Institute of Technology 114-96, Pasadena, California 91125, United States
| | - Oliver Einsle
- ‡Institut für Biochemie and BIOSS Centre for Biological Signaling Studies, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany
| | - Douglas C Rees
- †Division of Chemistry and Chemical Engineering, California Institute of Technology 114-96, Pasadena, California 91125, United States.,§Howard Hughes Medical Institute, California Institute of Technology, Pasadena, California 91125, United States
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22
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Liang A, Lippard SJ. Component interactions and electron transfer in toluene/o-xylene monooxygenase. Biochemistry 2014; 53:7368-75. [PMID: 25402597 PMCID: PMC4255640 DOI: 10.1021/bi500892n] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Revised: 10/28/2014] [Indexed: 01/19/2023]
Abstract
The multicomponent protein toluene/o-xylene monooxygenase (ToMO) activates molecular oxygen to oxidize aromatic hydrocarbons. Prior to dioxygen activation, two electrons are injected into each of two diiron(III) units of the hydroxylase, a process that involves three redox active proteins: the ToMO hydroxylase (ToMOH), Rieske protein (ToMOC), and an NADH oxidoreductase (ToMOF). In addition to these three proteins, a small regulatory protein is essential for catalysis (ToMOD). Through steady state and pre-steady state kinetics studies, we show that ToMOD attenuates electron transfer from ToMOC to ToMOH in a concentration-dependent manner. At substoichiometric concentrations, ToMOD increases the rate of turnover, which we interpret to be a consequence of opening a pathway for oxygen transport to the catalytic diiron center in ToMOH. Excess ToMOD inhibits steady state catalysis in a manner that depends on ToMOC concentration. Through rapid kinetic assays, we demonstrate that ToMOD attenuates formation of the ToMOC-ToMOH complex. These data, coupled with protein docking studies, support a competitive model in which ToMOD and ToMOC compete for the same binding site on the hydroxylase. These results are discussed in the context of other studies of additional proteins in the superfamily of bacterial multicomponent monooxygenases.
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Affiliation(s)
- Alexandria
Deliz Liang
- Department of Chemistry, Massachusetts
Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Stephen J. Lippard
- Department of Chemistry, Massachusetts
Institute of Technology, Cambridge, Massachusetts 02139, United States
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23
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Acheson JF, Bailey LJ, Elsen NL, Fox BG. Structural basis for biomolecular recognition in overlapping binding sites in a diiron enzyme system. Nat Commun 2014; 5:5009. [PMID: 25248368 PMCID: PMC4200526 DOI: 10.1038/ncomms6009] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2014] [Accepted: 08/18/2014] [Indexed: 12/23/2022] Open
Abstract
Productive biomolecular recognition requires exquisite control of affinity and specificity. Accordingly, nature has devised many strategies to achieve proper binding interactions. Bacterial multicomponent monooxygenases provide a fascinating example, where a diiron hydroxylase must reversibly interact with both ferredoxin and catalytic effector in order to achieve electron transfer and O2 activation during catalysis. Because these two accessory proteins have distinct structures, and because the hydroxylase-effector complex covers the entire surface closest to the hydroxylase diiron centre, how ferredoxin binds to the hydroxylase has been unclear. Here we present high-resolution structures of toluene 4-monooxygenase hydroxylase complexed with its electron transfer ferredoxin and compare them with the hydroxylase-effector structure. These structures reveal that ferredoxin or effector protein binding produce different arrangements of conserved residues and customized interfaces on the hydroxylase in order to achieve different aspects of catalysis.
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Affiliation(s)
- Justin F Acheson
- Department of Biochemistry, University of Wisconsin, Biochemistry Addition, 433 Babcock Drive, Madison, Wisconsin 53706, USA
| | - Lucas J Bailey
- Department of Biochemistry, University of Wisconsin, Biochemistry Addition, 433 Babcock Drive, Madison, Wisconsin 53706, USA
| | - Nathaniel L Elsen
- Department of Biochemistry, University of Wisconsin, Biochemistry Addition, 433 Babcock Drive, Madison, Wisconsin 53706, USA
| | - Brian G Fox
- Department of Biochemistry, University of Wisconsin, Biochemistry Addition, 433 Babcock Drive, Madison, Wisconsin 53706, USA
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24
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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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25
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Wang W, Iacob RE, Luoh RP, Engen JR, Lippard SJ. Electron transfer control in soluble methane monooxygenase. J Am Chem Soc 2014; 136:9754-62. [PMID: 24937475 PMCID: PMC4105053 DOI: 10.1021/ja504688z] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
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The
hydroxylation or epoxidation of hydrocarbons by bacterial multicomponent
monooxygenases (BMMs) requires the interplay of three or four protein
components. How component protein interactions control catalysis,
however, is not well understood. In particular, the binding sites
of the reductase components on the surface of their cognate hydroxylases
and the role(s) that the regulatory proteins play during intermolecular
electron transfer leading to the hydroxylase reduction have been enigmatic.
Here we determine the reductase binding site on the hydroxylase of
a BMM enzyme, soluble methane monooxygenase (sMMO) from Methylococcus
capsulatus (Bath). We present evidence that the ferredoxin
domain of the reductase binds to the canyon region of the hydroxylase,
previously determined to be the regulatory protein binding site as
well. The latter thus inhibits reductase binding to the hydroxylase
and, consequently, intermolecular electron transfer from the reductase
to the hydroxylase diiron active site. The binding competition between
the regulatory protein and the reductase may serve as a control mechanism
for regulating electron transfer, and other BMM enzymes are likely
to adopt the same mechanism.
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Affiliation(s)
- Weixue Wang
- Departments of †Chemistry and §Biological Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States
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26
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Liang AD, Wrobel AT, Lippard SJ. A flexible glutamine regulates the catalytic activity of toluene o-xylene monooxygenase. Biochemistry 2014; 53:3585-92. [PMID: 24873259 PMCID: PMC4059525 DOI: 10.1021/bi500387y] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
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Toluene/o-xylene
monooxygenase (ToMO) is a bacterial
multicomponent monooxygenase capable of oxidizing aromatic substrates.
The carboxylate-rich diiron active site is located in the hydroxylase
component of ToMO (ToMOH), buried 12 Å from the surface of the
protein. A small, hydrophilic pore is the shortest pathway between
the diiron active site and the protein exterior. In this study of
ToMOH from Pseudomonas sp. OX1, the
functions of two residues lining this pore, N202 and Q228, were investigated
using site-directed mutagenesis. Steady-state characterization of
WT and the three mutant enzymes demonstrates that residues N202 and
Q228 are critical for turnover. Kinetic isotope effects and pH profiles
reveal that these residues govern the kinetics of water egress and
prevent quenching of activated oxygen intermediates formed at the
diiron active site. We propose that this activity arises from movement
of these residues, opening and closing the pore during catalysis,
as seen in previous X-ray crystallographic studies. In addition, N202
and Q228 are important for the interactions of the reductase and regulatory
components to ToMOH, suggesting that they bind competitively to the
hydroxylase. The role of the pore in the hydroxylase components of
other bacterial multicomponent monooxygenases within the superfamily
is discussed in light of these conclusions.
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Affiliation(s)
- Alexandria Deliz Liang
- Department of Chemistry, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States
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27
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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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28
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Hydroquinone: environmental pollution, toxicity, and microbial answers. BIOMED RESEARCH INTERNATIONAL 2013; 2013:542168. [PMID: 23936816 PMCID: PMC3727088 DOI: 10.1155/2013/542168] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/28/2013] [Accepted: 06/20/2013] [Indexed: 12/12/2022]
Abstract
Hydroquinone is a major benzene metabolite, which is a well-known haematotoxic and carcinogenic agent associated with malignancy in occupational environments. Human exposure to hydroquinone can occur by dietary, occupational, and environmental sources. In the environment, hydroquinone showed increased toxicity for aquatic organisms, being less harmful for bacteria and fungi. Recent pieces of evidence showed that hydroquinone is able to enhance carcinogenic risk by generating DNA damage and also to compromise the general immune responses which may contribute to the impaired triggering of the host immune reaction. Hydroquinone bioremediation from natural and contaminated sources can be achieved by the use of a diverse group of microorganisms, ranging from bacteria to fungi, which harbor very complex enzymatic systems able to metabolize hydroquinone either under aerobic or anaerobic conditions. Due to the recent research development on hydroquinone, this review underscores not only the mechanisms of hydroquinone biotransformation and the role of microorganisms and their enzymes in this process, but also its toxicity.
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29
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Lee SJ, McCormick MS, Lippard SJ, Cho US. Control of substrate access to the active site in methane monooxygenase. Nature 2013; 494:380-4. [PMID: 23395959 PMCID: PMC3596810 DOI: 10.1038/nature11880] [Citation(s) in RCA: 101] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Accepted: 12/21/2012] [Indexed: 11/16/2022]
Abstract
Methanotrophs consume methane as their major carbon source and have an essential role in the global carbon cycle by limiting escape of this greenhouse gas to the atmosphere. These bacteria oxidize methane to methanol by soluble and particulate methane monooxygenases (MMOs). Soluble MMO contains three protein components, a 251-kilodalton hydroxylase (MMOH), a 38.6-kilodalton reductase (MMOR), and a 15.9-kilodalton regulatory protein (MMOB), required to couple electron consumption with substrate hydroxylation at the catalytic diiron centre of MMOH. Until now, the role of MMOB has remained ambiguous owing to a lack of atomic-level information about the MMOH-MMOB (hereafter termed H-B) complex. Here we remedy this deficiency by providing a crystal structure of H-B, which reveals the manner by which MMOB controls the conformation of residues in MMOH crucial for substrate access to the active site. MMOB docks at the α(2)β(2) interface of α(2)β(2)γ(2) MMOH, and triggers simultaneous conformational changes in the α-subunit that modulate oxygen and methane access as well as proton delivery to the diiron centre. Without such careful control by MMOB of these substrate routes to the diiron active site, the enzyme operates as an NADH oxidase rather than a monooxygenase. Biological catalysis involving small substrates is often accomplished in nature by large proteins and protein complexes. The structure presented in this work provides an elegant example of this principle.
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Affiliation(s)
- Seung Jae Lee
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Michael S. McCormick
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Stephen J. Lippard
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Uhn-Soo Cho
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
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30
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Bailey LJ, Acheson JF, McCoy JG, Elsen NL, Phillips GN, Fox BG. Crystallographic analysis of active site contributions to regiospecificity in the diiron enzyme toluene 4-monooxygenase. Biochemistry 2012; 51:1101-13. [PMID: 22264099 DOI: 10.1021/bi2018333] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Crystal structures of toluene 4-monooxygenase hydroxylase in complex with reaction products and effector protein reveal active site interactions leading to regiospecificity. Complexes with phenolic products yield an asymmetric μ-phenoxo-bridged diiron center and a shift of diiron ligand E231 into a hydrogen bonding position with conserved T201. In contrast, complexes with inhibitors p-NH(2)-benzoate and p-Br-benzoate showed a μ-1,1 coordination of carboxylate oxygen between the iron atoms and only a partial shift in the position of E231. Among active site residues, F176 trapped the aromatic ring of products against a surface of the active site cavity formed by G103, E104 and A107, while F196 positioned the aromatic ring against this surface via a π-stacking interaction. The proximity of G103 and F176 to the para substituent of the substrate aromatic ring and the structure of G103L T4moHD suggest how changes in regiospecificity arise from mutations at G103. Although effector protein binding produced significant shifts in the positions of residues along the outer portion of the active site (T201, N202, and Q228) and in some iron ligands (E231 and E197), surprisingly minor shifts (<1 Å) were produced in F176, F196, and other interior residues of the active site. Likewise, products bound to the diiron center in either the presence or absence of effector protein did not significantly shift the position of the interior residues, suggesting that positioning of the cognate substrates will not be strongly influenced by effector protein binding. Thus, changes in product distributions in the absence of the effector protein are proposed to arise from differences in rates of chemical steps of the reaction relative to motion of substrates within the active site channel of the uncomplexed, less efficient enzyme, while structural changes in diiron ligand geometry associated with cycling between diferrous and diferric states are discussed for their potential contribution to product release.
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Affiliation(s)
- Lucas J Bailey
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706-1544, United States
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