1
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Lemen D, Rokita SE. Polar Interactions between Substrate and Flavin Control Iodotyrosine Deiodinase Function. Biochemistry 2024; 63:2380-2389. [PMID: 39213510 PMCID: PMC11408085 DOI: 10.1021/acs.biochem.4c00357] [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] [Indexed: 09/04/2024]
Abstract
Flavin cofactors offer a wide range of chemical mechanisms to support a great diversity in catalytic function. As a corollary, such diversity necessitates careful control within each flavoprotein to limit its function to an appropriate subset of possible reactions and substrates. This task falls to the protein environment surrounding the flavin in most enzymes. For iodotyrosine deiodinase that catalyzes a reductive dehalogenation of halotyrosines, substrates can dictate the chemistry available to the flavin. Their ability to stabilize the necessary one-electron reduced semiquinone form of flavin strictly depends on a direct coordination between the flavin and α-ammonium and carboxylate groups of its substrates. While perturbations to the carboxylate group do not significantly affect binding to the resting oxidized form of the deiodinase, dehalogenation (kcat/Km) is suppressed by over 2000-fold. Lack of the α-ammonium group abolishes detectable binding and dehalogenation. Substitution of the ammonium group with a hydroxyl group does not restore measurable binding but does support dehalogenation with an efficiency greater than those of the carboxylate derivatives. Consistent with these observations, the flavin semiquinone does not accumulate during redox titration in the presence of inert substrate analogues lacking either the α-ammonium or carboxylate groups. As a complement, a nitroreductase activity based on hydride transfer is revealed for the appropriate substrates with perturbations to their zwitterion.
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Affiliation(s)
- Daniel Lemen
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
| | - Steven E Rokita
- Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
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2
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Schröder GC, Meilleur F. Metalloprotein catalysis: structural and mechanistic insights into oxidoreductases from neutron protein crystallography. Acta Crystallogr D Struct Biol 2021; 77:1251-1269. [PMID: 34605429 PMCID: PMC8489226 DOI: 10.1107/s2059798321009025] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2021] [Accepted: 08/31/2021] [Indexed: 11/11/2022] Open
Abstract
Metalloproteins catalyze a range of reactions, with enhanced chemical functionality due to their metal cofactor. The reaction mechanisms of metalloproteins have been experimentally characterized by spectroscopy, macromolecular crystallography and cryo-electron microscopy. An important caveat in structural studies of metalloproteins remains the artefacts that can be introduced by radiation damage. Photoreduction, radiolysis and ionization deriving from the electromagnetic beam used to probe the structure complicate structural and mechanistic interpretation. Neutron protein diffraction remains the only structural probe that leaves protein samples devoid of radiation damage, even when data are collected at room temperature. Additionally, neutron protein crystallography provides information on the positions of light atoms such as hydrogen and deuterium, allowing the characterization of protonation states and hydrogen-bonding networks. Neutron protein crystallography has further been used in conjunction with experimental and computational techniques to gain insight into the structures and reaction mechanisms of several transition-state metal oxidoreductases with iron, copper and manganese cofactors. Here, the contribution of neutron protein crystallography towards elucidating the reaction mechanism of metalloproteins is reviewed.
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Affiliation(s)
- Gabriela C. Schröder
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, NC 27695, USA
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Flora Meilleur
- Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, NC 27695, USA
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
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3
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Kerber T, Vrielink A. The role of hydrogen atoms in redox catalysis by the flavoenzyme cholesterol oxidase. Methods Enzymol 2020; 634:361-377. [PMID: 32093840 DOI: 10.1016/bs.mie.2019.12.004] [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: 03/19/2023]
Abstract
Flavoenzymes comprise a large class of proteins that carry out a diverse range of important redox chemistry. Although X-ray crystal structures of many flavoenzymes have been determined, there are still unresolved questions regarding the actual oxidation state of the flavin cofactors in these structures due to photoreduction by the ionizing radiation of the X-ray beam during the diffraction experiment. Additionally, the ability to visualize hydrogen atoms in X-ray structures is difficult due to the weak scattering capability of these atoms. Since hydrogen atoms affect the electrostatic nature of enzyme active sites and play important roles in the chemistry of key amino acid residues, visualizing the precise positions of these atoms provides a more detailed understanding of their role in enzyme catalysis. Single crystal neutron diffraction is an alternative method to structure determination, circumventing problems associated with photoreduction of the sample thus providing a clearer view of the structural features of a flavoenzyme in different redox states. Additionally, the larger neutron scattering factors for hydrogen and deuterium atoms enables one to visualize these atoms much more easily than from X-ray scattering measurements. In this chapter we give an overview of neutron and X-ray crystallography studies on the flavoenzyme, cholesterol oxidase and how the observations of unusual hydrogen atom positions provide insight into the redox chemistry of the flavin cofactor.
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Affiliation(s)
- Tatiana Kerber
- School of Molecular Sciences, University of Western Australia, Perth, WA, Australia
| | - Alice Vrielink
- School of Molecular Sciences, University of Western Australia, Perth, WA, Australia.
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4
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Tai Y, Takaba K, Hanazono Y, Dao HA, Miki K, Takeda K. X-ray crystallographic studies on the hydrogen isotope effects of green fluorescent protein at sub-ångström resolutions. ACTA CRYSTALLOGRAPHICA SECTION D-STRUCTURAL BIOLOGY 2019; 75:1096-1106. [PMID: 31793903 DOI: 10.1107/s2059798319014608] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Accepted: 10/28/2019] [Indexed: 11/10/2022]
Abstract
Hydrogen atoms are critical to the nature and properties of proteins, and thus deuteration has the potential to influence protein function. In fact, it has been reported that some deuterated proteins show different physical and chemical properties to their protiated counterparts. Consequently, it is important to investigate protonation states around the active site when using deuterated proteins. Here, hydrogen isotope effects on the S65T/F99S/M153T/V163A variant of green fluorescent protein (GFP), in which the deprotonated B form is dominant at pH 8.5, were investigated. The pH/pD dependence of the absorption and fluorescence spectra indicates that the protonation state of the chromophore is the same in protiated GFP in H2O and protiated GFP in D2O at pH/pD 8.5, while the pKa of the chromophore became higher in D2O. Indeed, X-ray crystallographic analyses at sub-ångström resolution revealed no apparent changes in the protonation state of the chromophore between the two samples. However, detailed comparisons of the hydrogen OMIT maps revealed that the protonation state of His148 in the vicinity of the chromophore differed between the two samples. This indicates that protonation states around the active site should be carefully adjusted to be the same as those of the protiated protein when neutron crystallographic analyses of proteins are performed.
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Affiliation(s)
- Yang Tai
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Kiyofumi Takaba
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Yuya Hanazono
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Hoang Anh Dao
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Kunio Miki
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Kazuki Takeda
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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5
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Zhou S, Wang L. Unraveling the structural and chemical features of biological short hydrogen bonds. Chem Sci 2019; 10:7734-7745. [PMID: 31588321 PMCID: PMC6764281 DOI: 10.1039/c9sc01496a] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2019] [Accepted: 06/30/2019] [Indexed: 02/06/2023] Open
Abstract
Short hydrogen bonds are ubiquitous in biological macromolecules and exhibit distinctive proton potential energy surfaces and proton sharing properties.
The three-dimensional architecture of biomolecules often creates specialized structural elements, notably short hydrogen bonds that have donor–acceptor separations below 2.7 Å. In this work, we statistically analyze 1663 high-resolution biomolecular structures from the Protein Data Bank and demonstrate that short hydrogen bonds are prevalent in proteins, protein–ligand complexes and nucleic acids. From these biological macromolecules, we characterize the preferred location, connectivity and amino acid composition in short hydrogen bonds and hydrogen bond networks, and assess their possible functional importance. Using electronic structure calculations, we further uncover how the interplay of the structural and chemical features determines the proton potential energy surfaces and proton sharing conditions in biological short hydrogen bonds.
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Affiliation(s)
- Shengmin Zhou
- Department of Chemistry and Chemical Biology , Institute for Quantitative Biomedicine , Rutgers University , Piscataway , NJ 08854 , USA .
| | - Lu Wang
- Department of Chemistry and Chemical Biology , Institute for Quantitative Biomedicine , Rutgers University , Piscataway , NJ 08854 , USA .
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6
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Takaba K, Tai Y, Eki H, Dao HA, Hanazono Y, Hasegawa K, Miki K, Takeda K. Subatomic resolution X-ray structures of green fluorescent protein. IUCRJ 2019; 6:387-400. [PMID: 31098020 PMCID: PMC6503917 DOI: 10.1107/s205225251900246x] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Accepted: 02/17/2019] [Indexed: 05/06/2023]
Abstract
Green fluorescent protein (GFP) is a light-emitting protein that does not require a prosthetic group for its fluorescent activity. As such, GFP has become indispensable as a molecular tool in molecular biology. Nonetheless, there has been no subatomic elucidation of the GFP structure owing to the structural polymorphism around the chromophore. Here, subatomic resolution X-ray structures of GFP without the structural polymorphism are reported. The positions of H atoms, hydrogen-bonding network patterns and accurate geometric parameters were determined for the two protonated forms. Compared with previously determined crystal structures and theoretically optimized structures, the anionic chromophores of the structures represent the authentic resonance state of GFP. In addition, charge-density analysis based on atoms-in-molecules theory and noncovalent interaction analysis highlight weak but substantial interactions between the chromophore and the protein environment. Considered with the derived chemical indicators, the lone pair-π interactions between the chromophore and Thr62 should play a sufficient role in maintaining the electronic state of the chromophore. These results not only reveal the fine structural features that are critical to understanding the properties of GFP, but also highlight the limitations of current quantum-chemical calculations.
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Affiliation(s)
- Kiyofumi Takaba
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Yang Tai
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Haruhiko Eki
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Hoang-Anh Dao
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Yuya Hanazono
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Kazuya Hasegawa
- Protein Crystal Analysis Division, Japan Synchrotron Radiation Research Institute (JASRI), 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan
| | - Kunio Miki
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | - Kazuki Takeda
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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7
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Wongnate T, Surawatanawong P, Chuaboon L, Lawan N, Chaiyen P. The Mechanism of Sugar C−H Bond Oxidation by a Flavoprotein Oxidase Occurs by a Hydride Transfer Before Proton Abstraction. Chemistry 2019; 25:4460-4471. [DOI: 10.1002/chem.201806078] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Revised: 01/16/2019] [Indexed: 11/06/2022]
Affiliation(s)
- Thanyaporn Wongnate
- School of Biomolecular Science & EngineeringVidyasirimedhi Institute of Science and Technology (VISTEC), Wangchan Valley Rayong 21210 Thailand
| | - Panida Surawatanawong
- Department of Chemistry and Center of Excellence, for Innovation in ChemistryMahidol University Bangkok 10400 Thailand
| | - Litavadee Chuaboon
- Department of Biochemistry and Center for Excellence, in Protein and Enzyme Technology, Faculty of ScienceMahidol University Bangkok 10400 Thailand
| | - Narin Lawan
- Department of Chemistry, Faculty of ScienceChiang Mai University Chiang Mai 50200 Thailand
| | - Pimchai Chaiyen
- School of Biomolecular Science & EngineeringVidyasirimedhi Institute of Science and Technology (VISTEC), Wangchan Valley Rayong 21210 Thailand
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8
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Yu LJ, Golden E, Chen N, Zhao Y, Vrielink A, Karton A. Computational insights for the hydride transfer and distinctive roles of key residues in cholesterol oxidase. Sci Rep 2017; 7:17265. [PMID: 29222497 PMCID: PMC5722936 DOI: 10.1038/s41598-017-17503-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Accepted: 11/27/2017] [Indexed: 11/10/2022] Open
Abstract
Cholesterol oxidase (ChOx), a member of the glucose-methanol-choline (GMC) family, catalyzes the oxidation of the substrate via a hydride transfer mechanism and concomitant reduction of the FAD cofactor. Unlike other GMC enzymes, the conserved His447 is not the catalytic base that deprotonates the substrate in ChOx. Our QM/MM MD simulations indicate that the Glu361 residue acts as a catalytic base facilitating the hydride transfer from the substrate to the cofactor. We find that two rationally chosen point mutations (His447Gln and His447Asn) cause notable decreases in the catalytic activity. The binding free energy calculations show that the Glu361 and His447 residues are important in substrate binding. We also performed high-level double-hybrid density functional theory simulations using small model systems, which support the QM/MM MD results. Our work provides a basis for unraveling the substrate oxidation mechanism in GMC enzymes in which the conserved histidine does not act as a base.
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Affiliation(s)
- Li-Juan Yu
- School of Molecular Sciences, The University of Western Australia, Perth, WA, 6009, Australia
| | - Emily Golden
- School of Molecular Sciences, The University of Western Australia, Perth, WA, 6009, Australia
| | - Nanhao Chen
- School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou, 510006, China.,Department of Chemistry, University of California, Davis, California, 95616, United States
| | - Yuan Zhao
- The Key Laboratory of Natural Medicine and Immuno-Engineering, Henan University, Kaifeng, 475004, China.
| | - Alice Vrielink
- School of Molecular Sciences, The University of Western Australia, Perth, WA, 6009, Australia
| | - Amir Karton
- School of Molecular Sciences, The University of Western Australia, Perth, WA, 6009, Australia.
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9
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Harb LH, Arooj M, Vrielink A, Mancera RL. Computational site-directed mutagenesis studies of the role of the hydrophobic triad on substrate binding in cholesterol oxidase. Proteins 2017; 85:1645-1655. [PMID: 28508424 DOI: 10.1002/prot.25319] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 04/21/2017] [Accepted: 05/08/2017] [Indexed: 11/10/2022]
Abstract
Cholesterol oxidase (ChOx) is a flavoenzyme that oxidizes and isomerizes cholesterol (CHL) to form cholest-4-en-3-one. Molecular docking and molecular dynamics simulations were conducted to predict the binding interactions of CHL in the active site. Several key interactions (E361-CHL, N485-FAD, and H447-CHL) were identified and which are likely to determine the correct positioning of CHL relative to flavin-adenine dinucleotide (FAD). Binding of CHL also induced changes in key residues of the active site leading to the closure of the oxygen channel. A group of residues, Y107, F444, and Y446, known as the hydrophobic triad, are believed to affect the binding of CHL in the active site. Computational site-directed mutagenesis of these residues revealed that their mutation affects the conformations of key residues in the active site, leading to non-optimal binding of CHL and to changes in the structure of the oxygen channel, all of which are likely to reduce the catalytic efficiency of ChOx. Proteins 2017; 85:1645-1655. © 2017 Wiley Periodicals, Inc.
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Affiliation(s)
- Laith Hisham Harb
- School of Biomedical Sciences, Curtin Health Innovation Research Institute and Curtin Institute for Computation, Curtin University, Perth, WA, 6845, Australia
| | - Mahreen Arooj
- School of Biomedical Sciences, Curtin Health Innovation Research Institute and Curtin Institute for Computation, Curtin University, Perth, WA, 6845, Australia
| | - Alice Vrielink
- School of Chemistry and Biochemistry, University of Western Australia, Crawley, WA, 6009, Australia
| | - Ricardo L Mancera
- School of Biomedical Sciences, Curtin Health Innovation Research Institute and Curtin Institute for Computation, Curtin University, Perth, WA, 6845, Australia
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10
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Masuda T, Suzuki M, Inoue S, Song C, Nakane T, Nango E, Tanaka R, Tono K, Joti Y, Kameshima T, Hatsui T, Yabashi M, Mikami B, Nureki O, Numata K, Iwata S, Sugahara M. Atomic resolution structure of serine protease proteinase K at ambient temperature. Sci Rep 2017; 7:45604. [PMID: 28361898 PMCID: PMC5374539 DOI: 10.1038/srep45604] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Accepted: 03/01/2017] [Indexed: 01/24/2023] Open
Abstract
Atomic resolution structures (beyond 1.20 Å) at ambient temperature, which is usually hampered by the radiation damage in synchrotron X-ray crystallography (SRX), will add to our understanding of the structure-function relationships of enzymes. Serial femtosecond crystallography (SFX) has attracted surging interest by providing a route to bypass such challenges. Yet the progress on atomic resolution analysis with SFX has been rather slow. In this report, we describe the 1.20 Å resolution structure of proteinase K using 13 keV photon energy. Hydrogen atoms, water molecules, and a number of alternative side-chain conformations have been resolved. The increase in the value of B-factor in SFX suggests that the residues and water molecules adjacent to active sites were flexible and exhibited dynamic motions at specific substrate-recognition sites.
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Affiliation(s)
- Tetsuya Masuda
- Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.,RIKEN SPring-8 Center, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Mamoru Suzuki
- RIKEN SPring-8 Center, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.,Institute for Protein Research, Osaka University, Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Shigeyuki Inoue
- RIKEN SPring-8 Center, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.,Department of Cell Biology and Anatomy, Graduate School of Medicine, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Changyong Song
- RIKEN SPring-8 Center, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.,Department of Physics, POSTECH, Pohang 790-784, Korea
| | - Takanori Nakane
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Eriko Nango
- RIKEN SPring-8 Center, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Rie Tanaka
- RIKEN SPring-8 Center, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Kensuke Tono
- Japan Synchrotron Radiation Research Institute, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan
| | - Yasumasa Joti
- Japan Synchrotron Radiation Research Institute, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan
| | - Takashi Kameshima
- Japan Synchrotron Radiation Research Institute, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan
| | - Takaki Hatsui
- RIKEN SPring-8 Center, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Makina Yabashi
- RIKEN SPring-8 Center, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - Bunzo Mikami
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
| | - Osamu Nureki
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Keiji Numata
- Enzyme Research Team, Biomass Engineering Research Division, RIKEN Center for Sustainable Resource Science, Hirosawa, Wako-shi, Saitama 351-0198, Japan
| | - So Iwata
- RIKEN SPring-8 Center, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.,Department of Cell Biology, Graduate School of Medicine, Kyoto University, Yoshidakonoe-cho, Sakyo-ku, Kyoto 606-8501, Japan
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11
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An extended N-H bond, driven by a conserved second-order interaction, orients the flavin N5 orbital in cholesterol oxidase. Sci Rep 2017; 7:40517. [PMID: 28098177 PMCID: PMC5241826 DOI: 10.1038/srep40517] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Accepted: 12/06/2016] [Indexed: 02/06/2023] Open
Abstract
The protein microenvironment surrounding the flavin cofactor in flavoenzymes is key to the efficiency and diversity of reactions catalysed by this class of enzymes. X-ray diffraction structures of oxidoreductase flavoenzymes have revealed recurrent features which facilitate catalysis, such as a hydrogen bond between a main chain nitrogen atom and the flavin redox center (N5). A neutron diffraction study of cholesterol oxidase has revealed an unusual elongated main chain nitrogen to hydrogen bond distance positioning the hydrogen atom towards the flavin N5 reactive center. Investigation of the structural features which could cause such an unusual occurrence revealed a positively charged lysine side chain, conserved in other flavin mediated oxidoreductases, in a second shell away from the FAD cofactor acting to polarize the peptide bond through interaction with the carbonyl oxygen atom. Double-hybrid density functional theory calculations confirm that this electrostatic arrangement affects the N-H bond length in the region of the flavin reactive center. We propose a novel second-order partial-charge interaction network which enables the correct orientation of the hydride receiving orbital of N5. The implications of these observations for flavin mediated redox chemistry are discussed.
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12
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Coenzyme-like ligands for affinity isolation of cholesterol oxidase. J Chromatogr B Analyt Technol Biomed Life Sci 2016; 1021:169-174. [DOI: 10.1016/j.jchromb.2016.01.043] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Revised: 01/24/2016] [Accepted: 01/27/2016] [Indexed: 11/22/2022]
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13
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Golden E, Attwood PV, Duff AP, Meilleur F, Vrielink A. Production and characterization of recombinant perdeuterated cholesterol oxidase. Anal Biochem 2015; 485:102-8. [PMID: 26073659 DOI: 10.1016/j.ab.2015.06.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2015] [Revised: 06/04/2015] [Accepted: 06/05/2015] [Indexed: 10/23/2022]
Abstract
Cholesterol oxidase (CO) is a FAD (flavin adenine dinucleotide) containing enzyme that catalyzes the oxidization and isomerization of cholesterol. Studies directed toward elucidating the catalytic mechanism of CO will provide an important general understanding of Flavin-assisted redox catalysis. Hydrogen atoms play an important role in enzyme catalysis; however, they are not readily visualized in protein X-ray diffraction structures. Neutron crystallography is an ideal method for directly visualizing hydrogen positions at moderate resolutions because hydrogen and deuterium have comparable neutron scattering lengths to other heavy atoms present in proteins. The negative coherent and large incoherent scattering lengths of hydrogen atoms in neutron diffraction experiments can be circumvented by replacing hydrogen atoms with its isotope, deuterium. The perdeuterated form of CO was successfully expressed from minimal medium, purified, and crystallized. X-ray crystallographic structures of the enzyme in the perdeuterated and hydrogenated states confirm that there are no apparent structural differences between the two enzyme forms. Kinetic assays demonstrate that perdeuterated and hydrogenated enzymes are functionally identical. Together, structural and functional studies indicate that the perdeuterated protein is suitable for structural studies by neutron crystallography directed at understanding the role of hydrogen atoms in enzyme catalysis.
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Affiliation(s)
- Emily Golden
- School of Chemistry and Biochemistry, University of Western Australia, Crawley, WA 6009, Australia
| | - Paul V Attwood
- School of Chemistry and Biochemistry, University of Western Australia, Crawley, WA 6009, Australia
| | - Anthony P Duff
- Bragg Institute, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia
| | - Flora Meilleur
- Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA; Structural and Molecular Biochemistry, North Carolina State University, Raleigh, NC 27695, USA
| | - Alice Vrielink
- School of Chemistry and Biochemistry, University of Western Australia, Crawley, WA 6009, Australia.
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14
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Zarychta B, Lyubimov A, Ahmed M, Munshi P, Guillot B, Vrielink A, Jelsch C. Cholesterol oxidase: ultrahigh-resolution crystal structure and multipolar atom model-based analysis. ACTA ACUST UNITED AC 2015; 71:954-68. [PMID: 25849405 DOI: 10.1107/s1399004715002382] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2014] [Accepted: 02/04/2015] [Indexed: 11/10/2022]
Abstract
Examination of protein structure at the subatomic level is required to improve the understanding of enzymatic function. For this purpose, X-ray diffraction data have been collected at 100 K from cholesterol oxidase crystals using synchrotron radiation to an optical resolution of 0.94 Å. After refinement using the spherical atom model, nonmodelled bonding peaks were detected in the Fourier residual electron density on some of the individual bonds. Well defined bond density was observed in the peptide plane after averaging maps on the residues with the lowest thermal motion. The multipolar electron density of the protein-cofactor complex was modelled by transfer of the ELMAM2 charge-density database, and the topology of the intermolecular interactions between the protein and the flavin adenine dinucleotide (FAD) cofactor was subsequently investigated. Taking advantage of the high resolution of the structure, the stereochemistry of main-chain bond lengths and of C=O···H-N hydrogen bonds was analyzed with respect to the different secondary-structure elements.
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Affiliation(s)
- Bartosz Zarychta
- Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2), CNRS, UMR 7036, Institut Jean Barriol, Faculté des Sciences et Technologies, Université de Lorraine, BP 70239, 54506 Vandoeuvre-lès-Nancy CEDEX, France
| | - Artem Lyubimov
- Howard Hughes Medical Institute, Stanford, CA 94305-5432, USA
| | - Maqsood Ahmed
- Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2), CNRS, UMR 7036, Institut Jean Barriol, Faculté des Sciences et Technologies, Université de Lorraine, BP 70239, 54506 Vandoeuvre-lès-Nancy CEDEX, France
| | - Parthapratim Munshi
- Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2), CNRS, UMR 7036, Institut Jean Barriol, Faculté des Sciences et Technologies, Université de Lorraine, BP 70239, 54506 Vandoeuvre-lès-Nancy CEDEX, France
| | - Benoît Guillot
- Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2), CNRS, UMR 7036, Institut Jean Barriol, Faculté des Sciences et Technologies, Université de Lorraine, BP 70239, 54506 Vandoeuvre-lès-Nancy CEDEX, France
| | - Alice Vrielink
- School of Chemistry and Biochemistry, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
| | - Christian Jelsch
- Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2), CNRS, UMR 7036, Institut Jean Barriol, Faculté des Sciences et Technologies, Université de Lorraine, BP 70239, 54506 Vandoeuvre-lès-Nancy CEDEX, France
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15
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Neumann P, Tittmann K. Marvels of enzyme catalysis at true atomic resolution: distortions, bond elongations, hidden flips, protonation states and atom identities. Curr Opin Struct Biol 2014; 29:122-33. [PMID: 25460275 DOI: 10.1016/j.sbi.2014.11.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Revised: 10/31/2014] [Accepted: 11/03/2014] [Indexed: 10/24/2022]
Abstract
Although general principles of enzyme catalysis are fairly well understood nowadays, many important details of how exactly the substrate is bound and processed in an enzyme remain often invisible and as such elusive. In fortunate cases, structural analysis of enzymes can be accomplished at true atomic resolution thus making possible to shed light on otherwise concealed fine-structural traits of bound substrates, intermediates, cofactors and protein groups. We highlight recent structural studies of enzymes using ultrahigh-resolution X-ray protein crystallography showcasing its enormous potential as a tool in the elucidation of enzymatic mechanisms and in unveiling fundamental principles of enzyme catalysis. We discuss the observation of seemingly hyper-reactive, physically distorted cofactors and intermediates with elongated scissile substrate bonds, the detection of 'hidden' conformational and chemical equilibria and the analysis of protonation states with surprising findings. In delicate cases, atomic resolution is required to unambiguously disclose the identity of atoms as demonstrated for the metal cluster in nitrogenase. In addition to the pivotal structural findings and the implications for our understanding of enzyme catalysis, we further provide a practical framework for resolution enhancement through optimized data acquisition and processing.
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Affiliation(s)
- Piotr Neumann
- Abteilung für Molekulare Strukturbiologie, Institut für Mikrobiologie und Genetik, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Justus-von-Liebig-Weg 11, Georg-August-Universität Göttingen, Göttingen D-37077, Germany.
| | - Kai Tittmann
- Abteilung Molekulare Enzymologie, Göttinger Zentrum für Molekulare Biowissenschaften (GZMB), Justus-von-Liebig-Weg 11, Georg-August-Universität Göttingen, Göttingen D-37077, Germany.
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16
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Golden E, Karton A, Vrielink A. High-resolution structures of cholesterol oxidase in the reduced state provide insights into redox stabilization. ACTA ACUST UNITED AC 2014; 70:3155-66. [PMID: 25478834 DOI: 10.1107/s139900471402286x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Accepted: 10/17/2014] [Indexed: 01/09/2023]
Abstract
Cholesterol oxidase (CO) is a flavoenzyme that catalyzes the oxidation and isomerization of cholesterol to cholest-4-en-3-one. The reductive half reaction occurs via a hydride transfer from the substrate to the FAD cofactor. The structures of CO reduced with dithionite under aerobic conditions and in the presence of the substrate 2-propanol under both aerobic and anaerobic conditions are presented. The 1.32 Å resolution structure of the dithionite-reduced enzyme reveals a sulfite molecule covalently bound to the FAD cofactor. The isoalloxazine ring system displays a bent structure relative to that of the oxidized enzyme, and alternate conformations of a triad of aromatic residues near to the cofactor are evident. A 1.12 Å resolution anaerobically trapped reduced enzyme structure in the presence of 2-propanol does not show a similar bending of the flavin ring system, but does show alternate conformations of the aromatic triad. Additionally, a significant difference electron-density peak is observed within a covalent-bond distance of N5 of the flavin moiety, suggesting that a hydride-transfer event has occurred as a result of substrate oxidation trapping the flavin in the electron-rich reduced state. The hydride transfer generates a tetrahedral geometry about the flavin N5 atom. High-level density-functional theory calculations were performed to correlate the crystallographic findings with the energetics of this unusual arrangement of the flavin moiety. These calculations suggest that strong hydrogen-bond interactions between Gly120 and the flavin N5 centre may play an important role in these structural features.
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Affiliation(s)
- Emily Golden
- School of Chemistry and Biochemistry, University of Western Australia, Crawley, Western Australia 6009, Australia
| | - Amir Karton
- School of Chemistry and Biochemistry, University of Western Australia, Crawley, Western Australia 6009, Australia
| | - Alice Vrielink
- School of Chemistry and Biochemistry, University of Western Australia, Crawley, Western Australia 6009, Australia
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17
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Romero E, Gadda G. Alcohol oxidation by flavoenzymes. Biomol Concepts 2014; 5:299-318. [DOI: 10.1515/bmc-2014-0016] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Accepted: 08/05/2014] [Indexed: 12/26/2022] Open
Abstract
AbstractThis review article describes the occurrence, general properties, and substrate specificity of the flavoenzymes belonging to the glucose-methanol-choline oxidoreductase superfamily and the l-α-hydroxyacid dehydrogenase family. Most of these enzymes catalyze the oxidations of hydroxyl groups, yielding carbonyl moieties. Over the years, carbanion, hydride transfer, and radical mechanisms have been discussed for these enzymes, and the main experimental evidences supporting these mechanisms are presented here. Regardless of the chemical nature of the organic substrate (i.e., activated and non-activated alcohols), a hydride transfer mechanism appears to be the most plausible for the flavoenzymes acting on CH-OH groups. The reaction of most of these enzymes likely starts with proton abstraction from the substrate hydroxyl group by a conserved active site histidine. Among the different approaches carried out to determine the chemical mechanisms with physiological substrates, primary substrate and solvent deuterium kinetic isotope effect studies have provided the most unambiguous evidences. It is expected that the numerous studies reported for these enzymes over the years will be instrumental in devising efficient industrial biocatalysts and drugs.
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Affiliation(s)
- Elvira Romero
- 1Department of Chemistry, Georgia State University, Atlanta, GA 30302-3965, USA
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18
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Lakshmi B, Sinduja C, Archunan G, Srinivasan N. Ramachandran analysis of conserved glycyl residues in homologous proteins of known structure. Protein Sci 2014; 23:843-50. [PMID: 24687432 DOI: 10.1002/pro.2468] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Revised: 03/16/2014] [Accepted: 03/25/2014] [Indexed: 11/10/2022]
Abstract
High conservation of glycyl residues in homologous proteins is fairly frequent. It is commonly understood that glycine tends to be highly conserved either because of its unique Ramachandran angles or to avoid steric clash that would arise with a larger side chain. Using a database of aligned 3D structures of homologous proteins we identified conserved Gly in 288 alignment positions from 85 families. Ninety-six of these alignment positions correspond to conserved Gly residue with (φ, ψ) values allowed for non-glycyl residues. Reasons for this observation were investigated by in-silico mutation of these glycyl residues to Ala. We found in 94% of the cases a short contact exists between the C(β) atom of the introduced Ala with the atoms which are often distant in the primary structure. This suggests the lack of space even for a short side chain thereby explaining high conservation of glycyl residues even when they adopt (φ, ψ) values allowed for Ala. In 189 alignment positions, the conserved glycyl residues adopt (φ, ψ) values which are disallowed for Ala. In-silico mutation of these Gly residues to Ala almost always results in steric hindrance involving C(β) atom of Ala as one would expect by comparing Ramachandran maps for Ala and Gly. Rare occurrence of the disallowed glycyl conformations even in ultrahigh resolution protein structures are accompanied by short contacts in the crystal structures and such disallowed conformations are not conserved in the homologues. These observations raise the doubt on the accuracy of such glycyl conformations in proteins.
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Affiliation(s)
- Balasubramanian Lakshmi
- Department of Animal Science, Bharathidasan University, Tiruchirappalli, 620024, Tamil Nadu, India; Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560012, Karnataka, India
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19
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Wanninayake U, Walker KD. A Bacterial Tyrosine Aminomutase Proceeds through Retention or Inversion of Stereochemistry To Catalyze Its Isomerization Reaction. J Am Chem Soc 2013; 135:11193-204. [DOI: 10.1021/ja403918w] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Udayanga Wanninayake
- Department
of Chemistry, and ‡Department of Biochemistry and Molecular Biology, Michigan
State University, East Lansing, Michigan 48824, United States
| | - Kevin D. Walker
- Department
of Chemistry, and ‡Department of Biochemistry and Molecular Biology, Michigan
State University, East Lansing, Michigan 48824, United States
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20
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Fungal aryl-alcohol oxidase: a peroxide-producing flavoenzyme involved in lignin degradation. Appl Microbiol Biotechnol 2012; 93:1395-410. [DOI: 10.1007/s00253-011-3836-8] [Citation(s) in RCA: 121] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2011] [Revised: 12/06/2011] [Accepted: 12/09/2011] [Indexed: 11/30/2022]
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21
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Xin Y, Yang H, Xia X, Zhang L, Cheng C, Mou G, Shi J, Han Y, Wang W. Affinity purification of a cholesterol oxidase expressed in Escherichia coli. J Chromatogr B Analyt Technol Biomed Life Sci 2011; 879:853-8. [DOI: 10.1016/j.jchromb.2011.02.025] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2010] [Revised: 02/09/2011] [Accepted: 02/15/2011] [Indexed: 11/16/2022]
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22
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Yuan H, Gadda G. Importance of a Serine Proximal to the C(4a) and N(5) Flavin Atoms for Hydride Transfer in Choline Oxidase. Biochemistry 2011; 50:770-9. [DOI: 10.1021/bi101837u] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | - Giovanni Gadda
- Department of Chemistry
- Department of Biology
- The Center for Biotechnology and Drug Design
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23
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Abstract
The binding states of the substrates and the environment have significant influence on protein motion. We present the analysis of such motion derived from anisotropic atomic displacement parameters (ADPs) in a set of atomic resolution protein structures. Local structural motion caused by ligand binding as well as functional loops showing cooperative patterns of motion could be inferred. The results are in line with proposed protonation states, hydrogen bonding patterns and the location of distinctly flexible regions: we could locate the mobile active site loop in a virus integrase, distinguish the subdomains in RNAse A and hydroxynitrile lyase, and reconstruct the molecular architecture in a xylanase. We demonstrate that the ADP-based motion analysis provides information at high level of detail and that the structural changes needed for substrate attachment or release may be derived from single X-ray structures.
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Affiliation(s)
- Andrea Schmidt
- European Molecular Biology Laboratory, Hamburg Unit, c/o DESY, Notkestrasse 85, D-22607 Hamburg, Germany.
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24
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Sundaramoorthy M, Gold MH, Poulos TL. Ultrahigh (0.93A) resolution structure of manganese peroxidase from Phanerochaete chrysosporium: implications for the catalytic mechanism. J Inorg Biochem 2010; 104:683-90. [PMID: 20356630 PMCID: PMC2866031 DOI: 10.1016/j.jinorgbio.2010.02.011] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2009] [Revised: 02/23/2010] [Accepted: 02/25/2010] [Indexed: 10/19/2022]
Abstract
Manganese peroxidase (MnP) is an extracellular heme enzyme produced by the lignin-degrading white-rot fungus Phanerochaete chrysosporium. MnP catalyzes the peroxide-dependent oxidation of Mn(II) to Mn(III). The Mn(III) is released from the enzyme in complex with oxalate, enabling the oxalate-Mn(III) complex to serve as a diffusible redox mediator capable of oxidizing lignin, especially under the mediation of unsaturated fatty acids. One heme propionate and the side chains of Glu35, Glu39 and Asp179 have been identified as Mn(II) ligands in our previous crystal structures of native MnP. In our current work, new 0.93A and 1.05A crystal structures of MnP with and without bound Mn(II), respectively, have been solved. This represents only the sixth structure of a protein of this size at 0.93A resolution. In addition, this is the first structure of a heme peroxidase from a eukaryotic organism at sub-Angstrom resolution. These new structures reveal an ordering/disordering of the C-terminal loop, which is likely required for Mn binding and release. In addition, the catalytic Arg42 residue at the active site, normally thought to function only in the peroxide activation process, also undergoes ordering/disordering that is coupled to a transient H-bond with the Mn ligand, Glu39. Finally, these high-resolution structures also reveal the exact H atoms in several parts of the structure that are relevant to the catalytic mechanism.
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Affiliation(s)
| | - Michael H. Gold
- Department of Biochemistry and Molecular Biology, OGI School of Science and Engineering, Oregon Health and Science University, Portland, OR 97291-1000
| | - Thomas L. Poulos
- Departments of Molecular Biology & Biochemistry, Chemistry, and Pharmaceutical Sciences University of California, Irvine, CA 92697-3900
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25
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Abstract
Cholesterol oxidase is a bacterial-specific flavoenzyme that catalyzes the oxidation and isomerisation of steroids containing a 3beta hydroxyl group and a double bond at the Delta5-6 of the steroid ring system. The enzyme is a member of a large family of flavin-specific oxidoreductases and is found in two different forms: one where the flavin adenine dinucleotide (FAD) cofactor is covalently linked to the protein and one where the cofactor is non-covalently bound to the protein. These two enzyme forms have been extensively studied in order to gain insight into the mechanism of flavin-mediated oxidation and the relationship between protein structure and enzyme redox potential. More recently the enzyme has been found to play an important role in bacterial pathogenesis and hence further studies are focused on its potential use for future development of novel antibacterial therapeutic agents. In this review the biochemical, structural, kinetic and mechanistic features of the enzyme are discussed.
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26
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Rokita SE, Adler JM, McTamney PM, Watson JA. Efficient use and recycling of the micronutrient iodide in mammals. Biochimie 2010; 92:1227-35. [PMID: 20167242 DOI: 10.1016/j.biochi.2010.02.013] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2009] [Accepted: 02/11/2010] [Indexed: 01/09/2023]
Abstract
Daily ingestion of iodide alone is not adequate to sustain production of the thyroid hormones, tri- and tetraiodothyronine. Proper maintenance of iodide in vivo also requires its active transport into the thyroid and its salvage from mono- and diiodotyrosine that are formed in excess during hormone biosynthesis. The enzyme iodotyrosine deiodinase responsible for this salvage is unusual in its ability to catalyze a reductive dehalogenation reaction dependent on a flavin cofactor, FMN. Initial characterization of this enzyme was limited by its membrane association, difficult purification and poor stability. The deiodinase became amenable to detailed analysis only after identification and heterologous expression of its gene. Site-directed mutagenesis recently demonstrated that cysteine residues are not necessary for enzymatic activity in contrast to precedence set by other reductive dehalogenases. Truncation of the N-terminal membrane anchor of the deiodinase has provided a soluble and stable source of enzyme sufficient for crystallographic studies. The structure of an enzyme.substrate co-crystal has become invaluable for understanding the origins of substrate selectivity and the mutations causing thyroid disease in humans.
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Affiliation(s)
- Steven E Rokita
- Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA.
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27
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Lyubimov AY, Chen L, Sampson NS, Vrielink A. A hydrogen-bonding network is important for oxidation and isomerization in the reaction catalyzed by cholesterol oxidase. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2009; 65:1222-31. [PMID: 19923719 PMCID: PMC3089011 DOI: 10.1107/s0907444909037421] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2009] [Accepted: 09/16/2009] [Indexed: 11/10/2022]
Abstract
Cholesterol oxidase is a flavoenzyme that catalyzes the oxidation and isomerization of 3beta-hydroxysteroids. Structural and mutagenesis studies have shown that Asn485 plays a key role in substrate oxidation. The side chain makes an NH...pi interaction with the reduced form of the flavin cofactor. A N485D mutant was constructed to further test the role of the amide group in catalysis. The mutation resulted in a 1800-fold drop in the overall k(cat). Atomic resolution structures were determined for both the N485L and N485D mutants. The structure of the N485D mutant enzyme (at 1.0 A resolution) reveals significant perturbations in the active site. As predicted, Asp485 is oriented away from the flavin moiety, such that any stabilizing interaction with the reduced flavin is abolished. Met122 and Glu361 form unusual hydrogen bonds to the functional group of Asp485 and are displaced from the positions they occupy in the wild-type active site. The overall effect is to disrupt the stabilization of the reduced FAD cofactor during catalysis. Furthermore, a narrow transient channel that is shown to form when the wild-type Asn485 forms the NH...pi interaction with FAD and that has been proposed to function as an access route of molecular oxygen, is not observed in either of the mutant structures, suggesting that the dynamics of the active site are altered.
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Affiliation(s)
- Artem Y Lyubimov
- Department of Molecular, Cell and Developmental Biology, University of California, Santa Cruz, Sinsheimer Laboratories, Santa Cruz, CA 95064, USA
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28
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Ferreira P, Hernandez-Ortega A, Herguedas B, Martínez AT, Medina M. Aryl-alcohol oxidase involved in lignin degradation: a mechanistic study based on steady and pre-steady state kinetics and primary and solvent isotope effects with two alcohol substrates. J Biol Chem 2009; 284:24840-7. [PMID: 19574215 DOI: 10.1074/jbc.m109.011593] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Aryl-alcohol oxidase (AAO) is a FAD-containing enzyme in the GMC (glucose-methanol-choline oxidase) family of oxidoreductases. AAO participates in fungal degradation of lignin, a process of high ecological and biotechnological relevance, by providing the hydrogen peroxide required by ligninolytic peroxidases. In the Pleurotus species, this peroxide is generated in the redox cycling of p-anisaldehyde, an extracellular fungal metabolite. In addition to p-anisyl alcohol, the enzyme also oxidizes other polyunsaturated primary alcohols. Its reaction mechanism was investigated here using p-anisyl alcohol and 2,4-hexadien-1-ol as two AAO model substrates. Steady state kinetic parameters and enzyme-monitored turnover were consistent with a sequential mechanism in which O(2) reacts with reduced AAO before release of the aldehyde product. Pre-steady state analysis revealed that the AAO reductive half-reaction is essentially irreversible and rate limiting during catalysis. Substrate and solvent kinetic isotope effects under steady and pre-steady state conditions (the latter showing approximately 9-fold slower enzyme reduction when alpha-bideuterated substrates were used, and approximately 13-fold slower reduction when both substrate and solvent effects were simultaneously evaluated) revealed a synchronous mechanism in which hydride transfer from substrate alpha-carbon to FAD and proton abstraction from hydroxyl occur simultaneously. This significantly differs from the general mechanism proposed for other members of the GMC oxidoreductase family that implies hydride transfer from a previously stabilized substrate alkoxide.
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Affiliation(s)
- Patricia Ferreira
- Centro de Investigaciones Biológicas (CIB), Consejo Superior de Investigaciones Científicas (CSIC), E28040 Madrid, Spain
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29
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Thomas SR, McTamney PM, Adler JM, Laronde-Leblanc N, Rokita SE. Crystal structure of iodotyrosine deiodinase, a novel flavoprotein responsible for iodide salvage in thyroid glands. J Biol Chem 2009; 284:19659-67. [PMID: 19436071 DOI: 10.1074/jbc.m109.013458] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The flavoprotein iodotyrosine deiodinase (IYD) salvages iodide from mono- and diiodotyrosine formed during the biosynthesis of the thyroid hormone thyroxine. Expression of a soluble domain of this membrane-bound enzyme provided sufficient material for crystallization and characterization by x-ray diffraction. The structures of IYD and two co-crystals containing substrates, mono- and diiodotyrosine, alternatively, were solved at resolutions of 2.0, 2.45, and 2.6 A, respectively. The structure of IYD is homologous to others in the NADH oxidase/flavin reductase superfamily, but the position of the active site lid in IYD defines a new subfamily within this group that includes BluB, an enzyme associated with vitamin B(12) biosynthesis. IYD and BluB also share key interactions involving their bound flavin mononucleotide that suggest a unique catalytic behavior within the superfamily. Substrate coordination to IYD induces formation of an additional helix and coil that act as an active site lid to shield the resulting substrate.flavin complex from solvent. This complex is stabilized by aromatic stacking and extensive hydrogen bonding between the substrate and flavin. The carbon-iodine bond of the substrate is positioned directly over the C-4a/N-5 region of the flavin to promote electron transfer. These structures now also provide a molecular basis for understanding thyroid disease based on mutations of IYD.
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Affiliation(s)
- Seth R Thomas
- Department of Chemistry and Biochemistry, Center for Biomolecular Structure and Organization, University of Maryland, College Park, Maryland 20742, USA
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30
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Ryan KS, Chakraborty S, Howard-Jones AR, Walsh CT, Ballou DP, Drennan CL. The FAD cofactor of RebC shifts to an IN conformation upon flavin reduction. Biochemistry 2009; 47:13506-13. [PMID: 19035832 PMCID: PMC3983088 DOI: 10.1021/bi801229w] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
RebC is a putative flavin hydroxylase functioning together with RebP to carry out a key step in the biosynthesis of rebeccamycin. To probe the mechanism of flavin-based chemistry in RebC, we solved the structure of RebC with reduced flavin. Upon flavin reduction, the RebC crystal undergoes a change in its unit cell dimension concurrent with a 5 A movement of the isoalloxazine ring, positioning the flavin ring adjacent to the substrate-binding pocket. Additionally, a disordered helix becomes ordered upon flavin reduction, closing off one side of the substrate-binding pocket. This structure, along with previously reported structures, increases our understanding of the RebC enzyme mechanism, indicating that either the reduction of the flavin itself or binding of substrate is sufficient to drive major conformational changes in RebC to generate a closed active site. Our finding that flavin reduction seals the active site such that substrate cannot enter suggests that our reduced flavin RebC structure is off-pathway and that substrate binding is likely to precede flavin reduction during catalysis. Along with kinetic data presented here, these structures suggest that the first cycle of catalysis in RebC may resemble that of p-hydroxybenzoate hydroxylase, with substrate binding promoting flavin reduction.
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Affiliation(s)
- Katherine S Ryan
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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31
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Chen L, Lyubimov AY, Brammer L, Vrielink A, Sampson NS. The binding and release of oxygen and hydrogen peroxide are directed by a hydrophobic tunnel in cholesterol oxidase. Biochemistry 2008; 47:5368-77. [PMID: 18410129 DOI: 10.1021/bi800228w] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The usage by enzymes of specific binding pathways for gaseous substrates or products is debated. The crystal structure of the redox enzyme cholesterol oxidase, determined at sub-angstrom resolution, revealed a hydrophobic tunnel that may serve as a binding pathway for oxygen and hydrogen peroxide. This tunnel is formed by a cascade of conformational rearrangements and connects the active site with the exterior surface of the protein. To elucidate the relationship between this tunnel and gas binding and release, three mutant enzymes were constructed to block the tunnel or its putative gate. Mutation of the proposed gating residue Asn485 to Asp or tunnel residue Phe359 or Gly347 to Trp or Asn reduces the catalytic efficiency of oxidation. The K mO 2 increases from 300 +/- 35 microM for the wild-type enzyme to 617 +/- 15 microM for the F359W mutant. The k cat for the F359W mutant-catalyzed reaction decreases 13-fold relative to that of the wild-type-catalyzed reaction. The N485D and G347N mutants could not be saturated with oxygen. Transfer of hydride from the sterol to the flavin prosthetic group is no longer rate-limiting for these tunnel mutants. The steady-state kinetics of both wild-type and tunnel mutant enzymes are consistent with formation of a ternary complex of steroid and oxygen during catalysis. Furthermore, kinetic cooperativity with respect to molecular oxygen is observed with the tunnel mutants, but not with the wild-type enzyme. A rate-limiting conformational change for binding and release of oxygen and hydrogen peroxide, respectively, is consistent with the cooperative kinetics. In the atomic-resolution structure of F359W, the indole ring of the tryptophan completely fills the tunnel and is observed in only a single conformation. The size of the indole is proposed to limit conformational rearrangement of residue 359 that leads to tunnel opening in the wild-type enzyme. Overall, these results substantiate the functional importance of the tunnel for substrate binding and product release.
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Affiliation(s)
- Lin Chen
- Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, USA
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32
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Zambianchi F, Fraaije M, Carrea G, de Gonzalo G, Rodríguez C, Gotor V, Ottolina G. Titration and Assignment of Residues that Regulate the Enantioselectivity of Phenylacetone Monooxygenase. Adv Synth Catal 2007. [DOI: 10.1002/adsc.200600598] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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33
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Shemella P, Pereira B, Zhang Y, Van Roey P, Belfort G, Garde S, Nayak SK. Mechanism for intein C-terminal cleavage: a proposal from quantum mechanical calculations. Biophys J 2006; 92:847-53. [PMID: 17085503 PMCID: PMC1779973 DOI: 10.1529/biophysj.106.092049] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Inteins are autocatalytic protein cleavage and splicing elements. A cysteine to alanine mutation at the N-terminal of inteins inhibits splicing and isolates the C-terminal cleavage reaction. Experiments indicate an enhanced C-terminal cleavage reaction rate upon decreasing the solution pH for the cleavage mutant, which cannot be explained by the existing mechanistic framework. We use intein crystal structure data and the information about conserved amino acids to perform semiempirical PM3 calculations followed by high-level density functional theory calculations in both gas phase and implicit solvent environments. Based on these calculations, we propose a detailed "low pH" mechanism for intein C-terminal cleavage. Water plays an important role in the proposed reaction mechanism, acting as an acid as well as a base. The protonation of the scissile peptide bond nitrogen by a hydronium ion is an important first step in the reaction. That step is followed by the attack of the C-terminal asparagine side chain on its carbonyl carbon, causing succinimide formation and simultaneous peptide bond cleavage. The computed reaction energy barrier in the gas phase is approximately 33 kcal/mol and reduces to approximately 25 kcal/mol in solution, close to the 21 kcal/mol experimentally observed at pH 6.0. This mechanism is consistent with the observed increase in C-terminal cleavage activity at low pH for the cleavage mutant of the Mycobacterium tuberculosis RecA mini-intein.
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Affiliation(s)
- Philip Shemella
- Department of Physics, Applied Physics and Astronomy, and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180, USA.
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De Colibus L, Mattevi A. New frontiers in structural flavoenzymology. Curr Opin Struct Biol 2006; 16:722-8. [PMID: 17070680 DOI: 10.1016/j.sbi.2006.10.003] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2006] [Revised: 09/14/2006] [Accepted: 10/13/2006] [Indexed: 11/29/2022]
Abstract
During the past few years, there have been exciting developments in the field of flavoenzymology. New flavoenzymes have been discovered that are implicated in a variety of biological processes, including cell signaling, chromatin remodeling and cell development. The structures of several of these new flavoenzymes have been described, as exemplified by crystallographic analyses of MICAL, histone demethylase LSD1 and tryptophan dehalogenase. In addition, new structural information has revealed the evolutionary and mechanistic complexity of the enzymes of the riboflavin biosynthetic pathway. The integration of the enzymology data with crystallographic studies at atomic resolution is resulting in unprecedented insight into the chemical and geometric properties underlying flavoenzyme function.
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Affiliation(s)
- Luigi De Colibus
- Dipartimento di Genetica e Microbiologia, Università di Pavia, Via Ferrata 1, 27100 Pavia, Italy
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Lyubimov AY, Lario PI, Moustafa I, Vrielink A. Erratum: Atomic resolution crystallography reveals how changes in pH shape the protein microenvironment. Nat Chem Biol 2006. [DOI: 10.1038/nchembio0606-346a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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