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Gao J, Li L, Shen S, Ai G, Wang B, Guo F, Yang T, Han H, Xu Z, Pan G, Fan K. Cofactor-independent C-C bond cleavage reactions catalyzed by the AlpJ family of oxygenases in atypical angucycline biosynthesis. Beilstein J Org Chem 2024; 20:1198-1206. [PMID: 38887580 PMCID: PMC11181247 DOI: 10.3762/bjoc.20.102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2023] [Accepted: 05/07/2024] [Indexed: 06/20/2024] Open
Abstract
Biosynthesis of atypical angucyclines involves unique oxidative B-ring cleavage and rearrangement reactions, which are catalyzed by AlpJ-family oxygenases, including AlpJ, JadG, and GilOII. Prior investigations established the essential requirement for FADH2/FMNH2 as cofactors when utilizing the quinone intermediate dehydrorabelomycin as a substrate. In this study, we unveil a previously unrecognized facet of these enzymes as cofactor-independent oxygenases when employing the hydroquinone intermediate CR1 as a substrate. The enzymes autonomously drive oxidative ring cleavage and rearrangement reactions of CR1, yielding products identical to those observed in cofactor-dependent reactions of AlpJ-family oxygenases. Furthermore, the AlpJ- and JadG-catalyzed reactions of CR1 could be quenched by superoxide dismutase, supporting a catalytic mechanism wherein the substrate CR1 reductively activates molecular oxygen, generating a substrate radical and the superoxide anion O2 •-. Our findings illuminate a substrate-controlled catalytic mechanism of AlpJ-family oxygenases, expanding the realm of cofactor-independent oxygenases. Notably, AlpJ-family oxygenases stand as a pioneering example of enzymes capable of catalyzing oxidative reactions in either an FADH2/FMNH2-dependent or cofactor-independent manner.
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Affiliation(s)
- Jinmin Gao
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, No. 1 Beichen West Road, Beijing 100101, China
- University of Chinese Academy of Sciences, No. 1 Yanqihu East Road, Beijing 101408, China
| | - Liyuan Li
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, No. 1 Beichen West Road, Beijing 100101, China
| | - Shijie Shen
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, No. 1 Beichen West Road, Beijing 100101, China
- University of Chinese Academy of Sciences, No. 1 Yanqihu East Road, Beijing 101408, China
| | - Guomin Ai
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, No. 1 Beichen West Road, Beijing 100101, China
| | - Bin Wang
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, No. 1 Beichen West Road, Beijing 100101, China
- University of Chinese Academy of Sciences, No. 1 Yanqihu East Road, Beijing 101408, China
| | - Fang Guo
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, No. 1 Beichen West Road, Beijing 100101, China
| | - Tongjian Yang
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, No. 1 Beichen West Road, Beijing 100101, China
- University of Chinese Academy of Sciences, No. 1 Yanqihu East Road, Beijing 101408, China
| | - Hui Han
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, No. 1 Beichen West Road, Beijing 100101, China
| | - Zhengren Xu
- State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, 38 Xueyuan Road, Beijing 100191, China
| | - Guohui Pan
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, No. 1 Beichen West Road, Beijing 100101, China
- University of Chinese Academy of Sciences, No. 1 Yanqihu East Road, Beijing 101408, China
| | - Keqiang Fan
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, No. 1 Beichen West Road, Beijing 100101, China
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2
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Gui C, Kalkreuter E, Liu YC, Li G, Steele AD, Yang D, Chang C, Shen B. Cofactorless oxygenases guide anthraquinone-fused enediyne biosynthesis. Nat Chem Biol 2024; 20:243-250. [PMID: 37945897 DOI: 10.1038/s41589-023-01476-2] [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: 03/21/2023] [Accepted: 10/10/2023] [Indexed: 11/12/2023]
Abstract
The anthraquinone-fused enediynes (AFEs) combine an anthraquinone moiety and a ten-membered enediyne core capable of generating a cytotoxic diradical species. AFE cyclization is triggered by opening the F-ring epoxide, which is also the site of the most structural diversity. Previous studies of tiancimycin A, a heavily modified AFE, have revealed a cryptic aldehyde blocking installation of the epoxide, and no unassigned oxidases could be predicted within the tnm biosynthetic gene cluster. Here we identify two consecutively acting cofactorless oxygenases derived from methyltransferase and α/β-hydrolase protein folds, TnmJ and TnmK2, respectively, that are responsible for F-ring tailoring in tiancimycin biosynthesis by comparative genomics. Further biochemical and structural characterizations reveal that the electron-rich AFE anthraquinone moiety assists in catalyzing deformylation, epoxidation and oxidative ring cleavage without exogenous cofactors. These enzymes therefore fill important knowledge gaps for the biosynthesis of this class of molecules and the underappreciated family of cofactorless oxygenases.
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Affiliation(s)
- Chun Gui
- Department of Chemistry, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, University of Florida, Jupiter, FL, USA
| | - Edward Kalkreuter
- Department of Chemistry, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, University of Florida, Jupiter, FL, USA
| | - Yu-Chen Liu
- Department of Chemistry, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, University of Florida, Jupiter, FL, USA
| | - Gengnan Li
- Department of Chemistry, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, University of Florida, Jupiter, FL, USA
| | - Andrew D Steele
- Department of Chemistry, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, University of Florida, Jupiter, FL, USA
| | - Dong Yang
- Department of Chemistry, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, University of Florida, Jupiter, FL, USA
- Natural Products Discovery Center, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, University of Florida, Jupiter, FL, USA
| | - Changsoo Chang
- Structural Biology Center, X-ray Science Division, Argonne National Laboratory, Lemont, IL, USA
| | - Ben Shen
- Department of Chemistry, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, University of Florida, Jupiter, FL, USA.
- Natural Products Discovery Center, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, University of Florida, Jupiter, FL, USA.
- Department of Molecular Medicine, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, University of Florida, Jupiter, FL, USA.
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3
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Metabolic Pathway of Phenol Degradation of a Cold-Adapted Antarctic Bacteria, Arthrobacter sp. Catalysts 2022. [DOI: 10.3390/catal12111422] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Phenol is an important pollutant widely discharged as a component of hydrocarbon fuels, but its degradation in cold regions is challenging due to the harsh environmental conditions. To date, there is little information available concerning the capability for phenol biodegradation by indigenous Antarctic bacteria. In this study, enzyme activities and genes encoding phenol degradative enzymes identified using whole genome sequencing (WGS) were investigated to determine the pathway(s) of phenol degradation of Arthrobacter sp. strains AQ5-05 and AQ5-06, originally isolated from Antarctica. Complete phenol degradative genes involved only in the ortho-cleavage were detected in both strains. This was validated using assays of the enzymes catechol 1,2-dioxygenase and catechol 2,3-dioxygenase, which indicated the activity of only catechol 1,2-dioxygenase in both strains, in agreement with the results from the WGS. Both strains were psychrotolerant with the optimum temperature for phenol degradation, being between 10 and 15 °C. This study suggests the potential use of cold-adapted bacteria in the bioremediation of phenol pollution in cold environments.
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4
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Ma GL, Tran HT, Low ZJ, Candra H, Pang LM, Cheang QW, Fang M, Liang ZX. Pathway Retrofitting Yields Insights into the Biosynthesis of Anthraquinone-Fused Enediynes. J Am Chem Soc 2021; 143:11500-11509. [PMID: 34293863 DOI: 10.1021/jacs.1c03911] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Anthraquinone-fused enediynes (AQEs) are renowned for their distinctive molecular architecture, reactive enediyne warhead, and potent anticancer activity. Although the first members of AQEs, i.e., dynemicins, were discovered three decades ago, how their nitrogen-containing carbon skeleton is synthesized by microbial producers remains largely a mystery. In this study, we showed that the recently discovered sungeidine pathway is a "degenerative" AQE pathway that contains upstream enzymes for AQE biosynthesis. Retrofitting the sungeidine pathway with genes from the dynemicin pathway not only restored the biosynthesis of the AQE skeleton but also produced a series of novel compounds likely as the cycloaromatized derivatives of chemically unstable biosynthetic intermediates. The results suggest a cascade of highly surprising biosynthetic steps leading to the formation of the anthraquinone moiety, the hallmark C8-C9 linkage via alkyl-aryl cross-coupling, and the characteristic epoxide functionality. The findings provide unprecedented insights into the biosynthesis of AQEs and pave the way for examining these intriguing biosynthetic enzymes.
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Affiliation(s)
- Guang-Lei Ma
- School of Biological Sciences, Nanyang Technological University, Singapore 637551
| | - Hoa Thi Tran
- School of Biological Sciences, Nanyang Technological University, Singapore 637551
| | - Zhen Jie Low
- School of Biological Sciences, Nanyang Technological University, Singapore 637551
| | - Hartono Candra
- School of Biological Sciences, Nanyang Technological University, Singapore 637551
| | - Li Mei Pang
- School of Biological Sciences, Nanyang Technological University, Singapore 637551
| | - Qing Wei Cheang
- School of Biological Sciences, Nanyang Technological University, Singapore 637551
| | - Mingliang Fang
- School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798
| | - Zhao-Xun Liang
- School of Biological Sciences, Nanyang Technological University, Singapore 637551
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5
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Ortega P, Zanchet A, Sanz-Sanz C, Gómez-Carrasco S, González-Sánchez L, Jambrina PG. DpgC-Catalyzed Peroxidation of 3,5-Dihydroxyphenylacetyl-CoA (DPA-CoA): Insights into the Spin-Forbidden Transition and Charge Transfer Mechanisms*. Chemistry 2020; 27:1700-1712. [PMID: 32975323 DOI: 10.1002/chem.202002993] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Indexed: 11/06/2022]
Abstract
Despite being a very strong oxidizing agent, most organic molecules are not oxidized in the presence of O2 at room temperature because O2 is a diradical whereas most organic molecules are closed-shell. Oxidation then requires a change in the spin state of the system, which is forbidden according to non-relativistic quantum theory. To overcome this limitation, oxygenases usually rely on metal or redox cofactors to catalyze the incorporation of, at least, one oxygen atom into an organic substrate. However, some oxygenases do not require any cofactor, and the detailed mechanism followed by these enzymes remains elusive. To fill this gap, here the mechanism for the enzymatic cofactor-independent oxidation of 3,5-dihydroxyphenylacetyl-CoA (DPA-CoA) is studied by combining multireference calculations on a model system with QM/MM calculations. Our results reveal that intersystem crossing takes place without requiring the previous protonation of molecular oxygen. The characterization of the electronic states reveals that electron transfer is concomitant with the triplet-singlet transition. The enzyme plays a passive role in promoting the intersystem crossing, although spontaneous reorganization of the water wire connecting the active site with the bulk presets the substrate for subsequent chemical transformations. The results show that the stabilization of the singlet radical-pair between dioxygen and enolate is enough to promote spin-forbidden reaction without the need for neither metal cofactors nor basic residues in the active site.
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Affiliation(s)
- Pablo Ortega
- Departamento de Química Física, University of Salamanca, Salamanca, 37008, Spain
| | - Alexandre Zanchet
- Departamento de Química Física, University of Salamanca, Salamanca, 37008, Spain.,Instituto de Física Fundamental (CSIC), Madrid, 28006, Spain
| | - Cristina Sanz-Sanz
- Departamento de Química Física Aplicada, University Autónoma de Madrid, Madrid, 28049, Spain
| | | | | | - Pablo G Jambrina
- Departamento de Química Física, University of Salamanca, Salamanca, 37008, Spain
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6
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Petsi M, Zografos AL. 2,5-Diketopiperazine Catalysts as Activators of Dioxygen in Oxidative Processes. ACS Catal 2020. [DOI: 10.1021/acscatal.0c01847] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Marina Petsi
- Department of Chemistry, Main University Campus, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
| | - Alexandros L. Zografos
- Department of Chemistry, Main University Campus, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
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7
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Ellis ES, MacHale LT, Szilagyi RK, DuBois JL. How Chemical Environment Activates Anthralin and Molecular Oxygen for Direct Reaction. J Org Chem 2020; 85:1315-1321. [PMID: 31830417 DOI: 10.1021/acs.joc.9b03133] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The role of the chemical environment in promoting anthralin/O2 reactions was discovered using neat solvents to model the amino acids of a cofactor-independent oxygenase. Experimental and computational results highlight the importance of the substrate-enolate, which is accessed via energetically small, escalating steps in which the ground-state keto-isomer is tautomerized to an enol and then ionized by solvent. The resulting ion-pair is poised for spontaneous electron transfer to O2. Similar activation may be exploited in biological/nonbiological oxidations involving O2.
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Affiliation(s)
- Emerald S Ellis
- Department of Chemistry and Biochemistry , Montana State University , P.O. Box 173400, Bozeman , Montana 59717 , United States
| | - Luke T MacHale
- Department of Chemistry and Biochemistry , Montana State University , P.O. Box 173400, Bozeman , Montana 59717 , United States
| | - Robert K Szilagyi
- Department of Chemistry and Biochemistry , Montana State University , P.O. Box 173400, Bozeman , Montana 59717 , United States
| | - Jennifer L DuBois
- Department of Chemistry and Biochemistry , Montana State University , P.O. Box 173400, Bozeman , Montana 59717 , United States
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8
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Kannappan B, Cummins PL, Gready JE. Mechanism of Oxygenase-Pathway Reactions Catalyzed by Rubisco from Large-Scale Kohn-Sham Density Functional Calculations. J Phys Chem B 2019; 123:2833-2843. [PMID: 30845802 DOI: 10.1021/acs.jpcb.9b00518] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ribulose 1,5-bisphosphate carboxylase-oxygenase (Rubisco) is the primary carbon-fixing enzyme in photosynthesis, fixing CO2 to a 5-carbon sugar, RuBP, in a series of five reactions. However, it also catalyzes an oxygenase reaction by O2 addition to the same enolized RuBP substrate in an analogous reaction series in the same active site, producing a waste product and loss of photosynthetic efficiency. Starting from RuBP, the reactions are enolization to the enediolate form, addition of CO2 or O2 to form the carboxy or peroxo adduct, hydration to form a gemdiolate, scission of the C2-C3 bond of the original RuBP, and stereospecific or nonstereospecific protonation to form two molecules of the 3-carbon PGA product, or one molecule of PGA, one of 2-carbon PG (waste product), and one water molecule. Reducing the loss of efficiency from the oxygenase reaction is an attractive means to increase crop productivity. However, lack of understanding of key aspects of the catalytic mechanisms for both the carboxylase and oxygenase reactions, particularly those involving proton exchanges and roles of water molecules, has stymied efforts at re-engineering Rubisco to reduce losses from the oxygenation reaction. As the stable form of molecular oxygen is the triplet biradical state (3O2), its reaction with near-universal singlet-state molecules is formally spin forbidden. Although in oxygenase enzymes, 3O2 activation is usually achieved by one-electron transfers using transition-metal ions or organic cofactors, recently, cofactor-less oxygenases in which the substrate itself is the source of the electron for 3O2 activation have been identified, but in all such cases an aromatic ring stabilizes the substrate's negative charge. Here we present the first large-scale Kohn-Sham density functional theory study of the reaction mechanism of the Rubisco oxygenase pathway. First, we show that the enediolate substrate complexed to Mg2+ and its ligands extends the region for charge delocalization and stabilization of its negative charge to allow formation of a caged biradical enediolate-O2 complex. Thus, Rubisco is a unique type of oxygenase without precedent in the literature. Second, for the O2 addition to proceed to the singlet peroxo-adduct intermediate, the system must undergo an intersystem crossing. We found that the presence of protonated LYS334 is required to stabilize this intermediate and that both factors (strongly stabilized anion and protonated LYS334) facilitate a barrier-less activation of 3O2. This finding supports our recent proposal that deoxygenation, that is, reversal of gas binding, is possible. Third, as neither CO2 nor O2 binds to the enzyme, our findings support the proposal from our recent carboxylase study that the observed KC or KO (Michaelis-Menten constants) in the steady-state kinetics reflect the respective adducts, carboxy or peroxo. Fourth, after computing hydration pathways with water addition both syn and anti to C3, we found, in contrast to the results of our carboxylation study indicating anti addition, that in the oxygenation reaction only syn-hydration is capable of producing a stable gemdiolate that facilitates the rate-limiting C2-C3 bond scission to final products. Fifth, we propose that an excess proton we previously found was required in the carboxylation reaction for activating the C2-C3 bond scission is utilized in the oxygenation reaction for the required elimination of a water molecule. In summary, despite its oxygenase handicap, Rubisco's success in directing 75% of its substrate through the carboxylation pathway can be considered impressively effective. Although native C3 Rubiscos are in a fix with unwanted activity of 3O2 hampering its primary carboxylase function, mechanistic differences presented here with findings in our recent carboxylase study for both the gas-addition and subsequent reactions provide some clues as to how creative Rubisco re-engineering may offer a solution to reducing the oxygenase activity.
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Affiliation(s)
- Babu Kannappan
- John Curtin School of Medical Research , The Australian National University , Canberra ACT 0200 , Australia
| | - Peter L Cummins
- John Curtin School of Medical Research , The Australian National University , Canberra ACT 0200 , Australia
| | - Jill E Gready
- John Curtin School of Medical Research , The Australian National University , Canberra ACT 0200 , Australia
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9
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Machovina MM, Ellis ES, Carney TJ, Brushett FR, DuBois JL. How a cofactor-free protein environment lowers the barrier to O 2 reactivity. J Biol Chem 2019; 294:3661-3669. [PMID: 30602564 DOI: 10.1074/jbc.ra118.006144] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Revised: 01/01/2019] [Indexed: 11/06/2022] Open
Abstract
Molecular oxygen (O2)-utilizing enzymes are among the most important in biology. The abundance of O2, its thermodynamic power, and the benign nature of its end products have raised interest in oxidases and oxygenases for biotechnological applications. Although most O2-dependent enzymes have an absolute requirement for an O2-activating cofactor, several classes of oxidases and oxygenases accelerate direct reactions between substrate and O2 using only the protein environment. Nogalamycin monooxygenase (NMO) from Streptomyces nogalater is a cofactor-independent enzyme that catalyzes rate-limiting electron transfer between its substrate and O2 Here, using enzyme-kinetic, cyclic voltammetry, and mutagenesis methods, we demonstrate that NMO initially activates the substrate, lowering its pKa by 1.0 unit (ΔG* = 1.4 kcal mol-1). We found that the one-electron reduction potential, measured for the deprotonated substrate both inside and outside the protein environment, increases by 85 mV inside NMO, corresponding to a ΔΔG 0' of 2.0 kcal mol-1 (0.087 eV) and that the activation barrier, ΔG ‡, is lowered by 4.8 kcal mol-1 (0.21 eV). Applying the Marcus model, we observed that this suggests a sizable decrease of 28 kcal mol-1 (1.4 eV) in the reorganization energy (λ), which constitutes the major portion of the protein environment's effect in lowering the reaction barrier. A similar role for the protein has been proposed in several cofactor-dependent systems and may reflect a broader trend in O2-utilizing proteins. In summary, NMO's protein environment facilitates direct electron transfer, and NMO accelerates rate-limiting electron transfer by strongly lowering the reorganization energy.
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Affiliation(s)
- Melodie M Machovina
- From the Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59715-3400 and
| | - Emerald S Ellis
- From the Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59715-3400 and
| | | | - Fikile R Brushett
- Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307
| | - Jennifer L DuBois
- From the Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59715-3400 and
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10
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Cantú Reinhard FG, DuBois JL, de Visser SP. Catalytic Mechanism of Nogalamycin Monoxygenase: How Does Nature Synthesize Antibiotics without a Metal Cofactor? J Phys Chem B 2018; 122:10841-10854. [DOI: 10.1021/acs.jpcb.8b09648] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Fabián G. Cantú Reinhard
- Manchester Institute of Biotechnology and School of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester M1 7DN, U.K
| | - Jennifer L. DuBois
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59715-3400, United States
| | - Sam P. de Visser
- Manchester Institute of Biotechnology and School of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester M1 7DN, U.K
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11
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Guengerich FP, Yoshimoto FK. Formation and Cleavage of C-C Bonds by Enzymatic Oxidation-Reduction Reactions. Chem Rev 2018; 118:6573-6655. [PMID: 29932643 DOI: 10.1021/acs.chemrev.8b00031] [Citation(s) in RCA: 154] [Impact Index Per Article: 25.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Many oxidation-reduction (redox) enzymes, particularly oxygenases, have roles in reactions that make and break C-C bonds. The list includes cytochrome P450 and other heme-based monooxygenases, heme-based dioxygenases, nonheme iron mono- and dioxygenases, flavoproteins, radical S-adenosylmethionine enzymes, copper enzymes, and peroxidases. Reactions involve steroids, intermediary metabolism, secondary natural products, drugs, and industrial and agricultural chemicals. Many C-C bonds are formed via either (i) coupling of diradicals or (ii) generation of unstable products that rearrange. C-C cleavage reactions involve several themes: (i) rearrangement of unstable oxidized products produced by the enzymes, (ii) oxidation and collapse of radicals or cations via rearrangement, (iii) oxygenation to yield products that are readily hydrolyzed by other enzymes, and (iv) activation of O2 in systems in which the binding of a substrate facilitates O2 activation. Many of the enzymes involve metals, but of these, iron is clearly predominant.
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Affiliation(s)
- F Peter Guengerich
- Department of Biochemistry , Vanderbilt University School of Medicine , Nashville , Tennessee 37232-0146 , United States.,Department of Chemistry , University of Texas-San Antonio , San Antonio , Texas 78249-0698 , United States
| | - Francis K Yoshimoto
- Department of Biochemistry , Vanderbilt University School of Medicine , Nashville , Tennessee 37232-0146 , United States.,Department of Chemistry , University of Texas-San Antonio , San Antonio , Texas 78249-0698 , United States
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12
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Bathellier C, Tcherkez G, Lorimer GH, Farquhar GD. Rubisco is not really so bad. PLANT, CELL & ENVIRONMENT 2018; 41:705-716. [PMID: 29359811 DOI: 10.1111/pce.13149] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2017] [Revised: 01/09/2018] [Accepted: 01/09/2018] [Indexed: 05/19/2023]
Abstract
Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is the most widespread carboxylating enzyme in autotrophic organisms. Its kinetic and structural properties have been intensively studied for more than half a century. Yet important aspects of the catalytic mechanism remain poorly understood, especially the oxygenase reaction. Because of its relatively modest turnover rate (a few catalytic events per second) and the competitive inhibition by oxygen, Rubisco is often viewed as an inefficient catalyst for CO2 fixation. Considerable efforts have been devoted to improving its catalytic efficiency, so far without success. In this review, we re-examine Rubisco's catalytic performance by comparison with other chemically related enzymes. We find that Rubisco is not especially slow. Furthermore, considering both the nature and the complexity of the chemical reaction, its kinetic properties are unremarkable. Although not unique to Rubisco, oxygenation is not systematically observed in enolate and enamine forming enzymes and cannot be considered as an inevitable consequence of the mechanism. It is more likely the result of a compromise between chemical and metabolic imperatives. We argue that a better description of Rubisco mechanism is still required to better understand the link between CO2 and O2 reactivity and the rationale of Rubisco diversification and evolution.
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Affiliation(s)
- Camille Bathellier
- Research School of Biology, College of Science, Australian National University, Canberra, 2601, ACT, Australia
| | - Guillaume Tcherkez
- Research School of Biology, College of Science, Australian National University, Canberra, 2601, ACT, Australia
| | - George H Lorimer
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, 27042, USA
| | - Graham D Farquhar
- Research School of Biology, College of Science, Australian National University, Canberra, 2601, ACT, Australia
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13
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Silva PJ. Refining the reaction mechanism of O 2 towards its co-substrate in cofactor-free dioxygenases. PeerJ 2016; 4:e2805. [PMID: 28028471 PMCID: PMC5178339 DOI: 10.7717/peerj.2805] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Accepted: 11/19/2016] [Indexed: 11/21/2022] Open
Abstract
Cofactor-less oxygenases perform challenging catalytic reactions between singlet co-substrates and triplet oxygen, in spite of apparently violating the spin-conservation rule. In 1-H-3-hydroxy-4-oxoquinaldine-2,4-dioxygenase, the active site has been suggested by quantum chemical computations to fine tune triplet oxygen reactivity, allowing it to interact rapidly with its singlet substrate without the need for spin inversion, and in urate oxidase the reaction is thought to proceed through electron transfer from the deprotonated substrate to an aminoacid sidechain, which then feeds the electron to the oxygen molecule. In this work, we perform additional quantum chemical computations on these two systems to elucidate several intriguing features unaddressed by previous workers. These computations establish that in both enzymes the reaction proceeds through direct electron transfer from co-substrate to O2 followed by radical recombination, instead of minimum-energy crossing points between singlet and triplet potential energy surfaces without formal electron transfer. The active site does not affect the reactivity of oxygen directly but is crucial for the generation of the deprotonated form of the co-substrates, which have redox potentials far below those of their protonated forms and therefore may transfer electrons to oxygen without sizeable thermodynamic barriers. This mechanism seems to be shared by most cofactor-less oxidases studied so far.
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Affiliation(s)
- Pedro J Silva
- FP-ENAS/Fac. de Ciências da Saúde, Universidade Fernando Pessoa , Porto , Portugal
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