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Torres-Guzman JC, Padilla-Guerrero IE, Cervantes-Quintero KY, Martinez-Vazquez A, Ibarra-Guzman M, Gonzalez-Hernandez GA. Peculiarities of nitronate monooxygenases and perspectives for in vivo and in vitro applications. Appl Microbiol Biotechnol 2021; 105:8019-8032. [PMID: 34655320 DOI: 10.1007/s00253-021-11623-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Revised: 09/20/2021] [Accepted: 09/21/2021] [Indexed: 12/14/2022]
Abstract
Nitroalkanes such as nitromethane, nitroethane, 1-nitropropane (1NP), and 2-nitropropane (2NP), derived from anthropogenic activities, are hazardous environmental pollutants due to their toxicity and carcinogenic activity. In nature, 3-nitropropionate (3NPA) and its derivatives are produced as a defense mechanism by many groups of organisms, including bacteria, fungi, insects, and plants. 3NPA is highly toxic as its conjugate base, propionate-3-nitronate (P3N), is a potent inhibitor of mitochondrial succinate dehydrogenase, essential to the tricarboxylic acid cycle, and can inhibit isocitrate lyase, a critical enzyme of the glyoxylate cycle. In response to these toxic compounds, several organisms on the phylogenetic scale express genes that code for enzymes involved in the catabolism of nitroalkanes: nitroalkane oxidases (NAOs) and nitronate monooxygenases (NMOs) (previously classified as nitropropane dioxygenases, NPDs). Two types of NMOs have been identified: class I and class II, which differ in structure, catalytic efficiency, and preferred substrates. This review focuses on the biochemical properties, structure, classification, and physiological functions of NMOs, and offers perspectives for their in vivo and in vitro applications. KEY POINTS: • Nitronate monooxygenases (NMOs) are key enzymes in nitroalkane catabolism. • NMO enzymes are involved in defense mechanisms in different organisms. • NMO applications include organic synthesis, biocatalysts, and bioremediation.
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Affiliation(s)
- Juan Carlos Torres-Guzman
- Biology Department, Division of Natural and Exact Sciences, University of Guanajuato, CP. 36000, Guanajuato, Mexico
| | | | | | - Azul Martinez-Vazquez
- Biology Department, Division of Natural and Exact Sciences, University of Guanajuato, CP. 36000, Guanajuato, Mexico
| | - Marcos Ibarra-Guzman
- Biology Department, Division of Natural and Exact Sciences, University of Guanajuato, CP. 36000, Guanajuato, Mexico
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2
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On the use of noncompetitive kinetic isotope effects to investigate flavoenzyme mechanism. Methods Enzymol 2019; 620:115-143. [PMID: 31072484 DOI: 10.1016/bs.mie.2019.03.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
This account describes the application of kinetic isotope effects (KIEs) to investigate the mechanistic properties of flavin dependent enzymes. Assays can be conducted during steady-state catalytic turnover of the flavoenzyme with its substrate or by using rapid-kinetic techniques to measure either the reductive or oxidative half-reactions of the enzyme. Great care should be taken to ensure that the observed effects are due to isotopic substitution and not other factors such as pH effects or changes in the solvent viscosity of the reaction mixture. Different types of KIEs are described along with a physical description of their origins and the unique information each can provide about the mechanism of an enzyme. Detailed experimental techniques are outlined with special emphasis on the proper controls and data analysis that must be carried out to avoid erroneous conclusions. Examples are provided for each type of KIE measurement from references in the literature. It is our hope that this article will clarify any confusion concerning the utility of KIEs in the study of flavoprotein mechanism and encourage their use by the community.
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Kim DW, Lee KS, Chi YM. Crystal structure of hypothetical protein PA4202 from Pseudomonas aeruginosa PAO1 in complex with nitroethane as a nitroalkane substrate. Biochem Biophys Res Commun 2018; 503:330-337. [PMID: 29885842 DOI: 10.1016/j.bbrc.2018.06.024] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Accepted: 06/07/2018] [Indexed: 11/26/2022]
Abstract
Nitroalkane oxidase (NAO) and nitronate monooxygenase (NMO) are two different types of nitroalkane oxidizing flavoenzymes identified in nature. A previous study suggested that the hypothetical protein PA4202 from Pseudomonas aeruginosa PAO1 is NMO and utilizes only anionic nitronates. However, the structural similarity between the PA4202 protein and Streptomyces ansochromogenes NAO has motivated investigation for what features of the two enzymes differentiate between the NAO and NMO activities. Herein, we report the crystal structure of PA4202 in a ternary complex with a neutral nitroethane (NE) and flavin mononucleotide (FMN) cofactor to elucidate the substrate recognition mechanism using a site-directed mutagenesis. The ternary complex structure indicates that the NE is bound with an orientation, which is poised for the proton transfer to H183 (which is the essential first catalytic step with nitroalkanes), and subsequent reactions with FMN. Moreover, a kinetic study reveals that the catalytic reactions of the wild type and H183 mutants PA4202s with nitroalkane substrates may yield the products of hydrogen peroxide and nitrite that are specified to NAO, although they show a low catalytic efficiency. Our results provide the first structure-based molecular insight into the substrate binding property of the hypothetical protein PA4202, including the interactions with neutral nitroalkanes as the substrate.
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Affiliation(s)
- Do Wan Kim
- Division of Biotechnology, College of Life Sciences, Korea University, Seoul, 02841, Republic of Korea
| | - Ki Seog Lee
- Department of Clinical Laboratory Science, College of Health Sciences, Catholic University of Pusan, Busan, 46252, Republic of Korea.
| | - Young Min Chi
- Division of Biotechnology, College of Life Sciences, Korea University, Seoul, 02841, Republic of Korea.
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Fitzpatrick PF. Nitroalkane oxidase: Structure and mechanism. Arch Biochem Biophys 2017; 632:41-46. [PMID: 28529198 DOI: 10.1016/j.abb.2017.05.012] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Revised: 05/16/2017] [Accepted: 05/17/2017] [Indexed: 11/18/2022]
Abstract
The flavoprotein nitroalkane oxidase catalyzes the oxidation of neutral nitroalkanes to the corresponding aldehydes or ketones, releasing nitrite and transferring electrons to O2 to form H2O2. A combination of solution and structural analyses have provided a detailed understanding of the mechanism of this enzyme.
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Affiliation(s)
- Paul F Fitzpatrick
- Department of Biochemistry and Structural Biology, The University of Texas Health Science Center, San Antonio, TX 78229, USA.
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Gadda G, Fitzpatrick PF. Solvent isotope and viscosity effects on the steady-state kinetics of the flavoprotein nitroalkane oxidase. FEBS Lett 2013; 587:2785-9. [PMID: 23660407 DOI: 10.1016/j.febslet.2013.04.021] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2013] [Revised: 04/22/2013] [Accepted: 04/23/2013] [Indexed: 01/13/2023]
Abstract
The flavoprotein nitroalkane oxidase catalyzes the oxidative denitrification of a broad range of primary and secondary nitroalkanes to yield the respective aldehydes or ketones, hydrogen peroxide and nitrite. With nitroethane as substrate the D2O(k(cat)/K(M)) value is 0.6 and the D2Ok(cat) value is 2.4. The k(cat) proton inventory is consistent with a single exchangeable proton in flight, while the k(cat)/K(M) is consistent with either a single proton in flight in the transition state or a medium effect. Increasing the solvent viscosity did not affect the k(cat) or k(cat)/K(M) value significantly, establishing that nitroethane binding is at equilibrium and that product release does not limit k(cat).
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Affiliation(s)
- Giovanni Gadda
- Department of Chemistry and the Center for Biotechnology and Drug Design, Georgia State University, Atlanta, GA 30303, USA
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Tormos JR, Taylor AB, Daubner SC, Hart PJ, Fitzpatrick PF. Identification of a hypothetical protein from Podospora anserina as a nitroalkane oxidase. Biochemistry 2010; 49:5035-41. [PMID: 20481475 PMCID: PMC2889615 DOI: 10.1021/bi100610e] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The flavoprotein nitroalkane oxidase (NAO) from Fusarium oxysporum catalyzes the oxidation of primary and secondary nitroalkanes to their respective aldehydes and ketones. Structurally, the enzyme is a member of the acyl-CoA dehydrogenase superfamily. To date no enzymes other than that from F. oxysporum have been annotated as NAOs. To identify additional potential NAOs, the available database was searched for enzymes in which the active site residues Asp402, Arg409, and Ser276 were conserved. Of the several fungal enzymes identified in this fashion, PODANSg2158 from Podospora anserina was selected for expression and characterization. The recombinant enzyme is a flavoprotein with activity on nitroalkanes comparable to the F. oxysporum NAO, although the substrate specificity is somewhat different. Asp399, Arg406, and Ser273 in PODANSg2158 correspond to the active site triad in F. oxysporum NAO. The k(cat)/K(M)-pH profile with nitroethane shows a pK(a) of 5.9 that is assigned to Asp399 as the active site base. Mutation of Asp399 to asparagine decreases the k(cat)/K(M) value for nitroethane over 2 orders of magnitude. The R406K and S373A mutations decrease this kinetic parameter by 64- and 3-fold, respectively. The structure of PODANSg2158 has been determined at a resolution of 2.0 A, confirming its identification as an NAO.
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Affiliation(s)
- José R Tormos
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229, USA
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7
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Valley MP, Fenny NS, Ali SR, Fitzpatrick PF. Characterization of active site residues of nitroalkane oxidase. Bioorg Chem 2010; 38:115-9. [PMID: 20056514 PMCID: PMC2847678 DOI: 10.1016/j.bioorg.2009.12.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2009] [Revised: 12/03/2009] [Accepted: 12/04/2009] [Indexed: 11/30/2022]
Abstract
The flavoenzyme nitroalkane oxidase catalyzes the oxidation of primary and secondary nitroalkanes to the corresponding aldehydes and ketones plus nitrite. The structure of the enzyme shows that Ser171 forms a hydrogen bond to the flavin N5, suggesting that it plays a role in catalysis. Cys397 and Tyr398 were previously identified by chemical modification as potential active site residues. To more directly probe the roles of these residues, the S171A, S171V, S171T, C397S, and Y398F enzymes have been characterized with nitroethane as substrate. The C397S and Y398 enzymes were less stable than the wild-type enzyme, and the C397S enzyme routinely contained a substoichiometric amount of FAD. Analysis of the steady-state kinetic parameters for the mutant enzymes, including deuterium isotope effects, establishes that all of the mutations result in decreases in the rate constants for removal of the substrate proton by approximately 5-fold and decreases in the rate constant for product release of approximately 2-fold. Only the S171V and S171T mutations alter the rate constant for flavin oxidation. These results establish that these residues are not involved in catalysis, but rather are required for maintaining the protein structure.
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Affiliation(s)
- Michael P. Valley
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
| | - Nana S. Fenny
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
| | - Shah R. Ali
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
| | - Paul F. Fitzpatrick
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, TX 78229
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Pozzi MH, Gawandi V, Fitzpatrick PF. Mechanistic studies of para-substituted N,N'-dibenzyl-1,4-diaminobutanes as substrates for a mammalian polyamine oxidase. Biochemistry 2009; 48:12305-13. [PMID: 19911805 PMCID: PMC2797579 DOI: 10.1021/bi901694s] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The kinetics of oxidation of a series of para-substituted N,N'-dibenzyl-1,4-diaminobutanes by the flavoprotein polyamine oxidase from mouse have been determined to gain insight into the mechanism of amine oxidation by this member of the monoamine oxidase structural family. The k(cat)/K(m) values are maximal at pH 9, consistent with the singly charged substrate being the active form. The rate constant for flavin reduction, k(red), by N,N'-dibenzyl-1,4-diaminobutane decreases about 5-fold below a pK(a) of approximately 8; this is attributed to the need for a neutral nitrogen at the site of oxidation. The k(red) and k(cat) values are comparable for each of the N,N'-dibenzyl-1,4-diaminobutanes, consistent with rate-limiting reduction. The deuterium kinetic isotope effects on k(red) and k(cat) are identical for each of the N,N'-dibenzyl-1,4-diaminobutanes, consistent with rate-limiting cleavage of the substrate CH bond. The k(red) values for seven different para-substituted N,N'-dibenzyl-1,4-diaminobutanes correlate with a combination of the van der Waals volume and sigma value of the substrates, with rho values of -0.59 at pH 8.6 and -0.09 at pH 6.6. These results are consistent with direct transfer of a hydride from the neutral CN bond of the substrate to the flavin as the mechanism of polyamine oxidase.
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Affiliation(s)
| | - Vijay Gawandi
- Department of Biochemistry and Biophysics Texas A&M University, College Station TX 77843-2128
| | - Paul F. Fitzpatrick
- Department of Biochemistry University of Texas Health Science Center at San Antonio, San Antonio TX 78229-3900
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Gadda G, Francis K. Nitronate monooxygenase, a model for anionic flavin semiquinone intermediates in oxidative catalysis. Arch Biochem Biophys 2009; 493:53-61. [PMID: 19577534 DOI: 10.1016/j.abb.2009.06.018] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2009] [Revised: 06/24/2009] [Accepted: 06/28/2009] [Indexed: 11/26/2022]
Abstract
Nitronate monooxygenase (NMO), formerly referred to as 2-nitropropane dioxygenase, is an FMN-dependent enzyme that uses molecular oxygen to oxidize (anionic) alkyl nitronates and, in the case of the enzyme from Neurospora crassa, (neutral) nitroalkanes to the corresponding carbonyl compounds and nitrite. Over the past 5 years, a resurgence of interest on the enzymology of NMO has driven several studies aimed at the elucidation of the mechanistic and structural properties of the enzyme. This review article summarizes the knowledge gained from these studies on NMO, which has been emerging as a model system for the investigation of anionic flavosemiquinone intermediates in the oxidative catalysis of organic molecules, and for the effect that branching of reaction intermediates has on both the kinetic parameters and isotope effects associated with enzymatic reactions. A comparison of the catalytic mechanism of NMO with other flavin-dependent enzymes that oxidize nitroalkane and nitronates is also presented.
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Affiliation(s)
- Giovanni Gadda
- Department of Chemistry, Georgia State University, Atlanta, GA 30302-4098, USA.
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Héroux A, Bozinovski DM, Valley MP, Fitzpatrick PF, Orville AM. Crystal structures of intermediates in the nitroalkane oxidase reaction. Biochemistry 2009; 48:3407-16. [PMID: 19265437 DOI: 10.1021/bi8023042] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The flavoenzyme nitroalkane oxidase is a member of the acyl-CoA dehydrogenase superfamily. Nitroalkane oxidase catalyzes the oxidation of neutral nitroalkanes to nitrite and the corresponding aldehydes or ketones. Crystal structures to 2.2 A resolution or better of enzyme complexes with bound substrates and of a trapped substrate-flavin adduct are described. The D402N enzyme has no detectable activity with neutral nitroalkanes [Valley, M. P., and Fitzpatrick, P. F. (2003) J. Am. Chem. Soc. 125, 8738-8739]. The structure of the D402N enzyme crystallized in the presence of 1-nitrohexane or 1-nitrooctane shows the presence of the substrate in the binding site. The aliphatic chain of the substrate extends into a tunnel leading to the enzyme surface. The oxygens of the substrate nitro group interact both with amino acid residues and with the 2'-hydroxyl of the FAD. When nitroalkane oxidase oxidizes nitroalkanes in the presence of cyanide, an electrophilic flavin imine intermediate can be trapped [Valley, M. P., Tichy, S. E., and Fitzpatrick, P. F. (2005) J. Am. Chem. Soc. 127, 2062-2066]. The structure of the enzyme trapped with cyanide during oxidation of 1-nitrohexane shows the presence of the modified flavin. A continuous hydrogen bond network connects the nitrogen of the CN-hexyl-FAD through the FAD 2'-hydroxyl to a chain of water molecules extending to the protein surface. Together, our complementary approaches provide strong evidence that the flavin cofactor is in the appropriate oxidation state and correlates well with the putative intermediate state observed within each of the crystal structures. Consequently, these results provide important structural descriptions of several steps along the nitroalkane oxidase reaction cycle.
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Affiliation(s)
- Annie Héroux
- Department of Biology, Brookhaven National Laboratory, Upton, New York 11973, USA
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