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Russo S, Rozeboom HJ, Wijma HJ, Poelarends GJ, Fraaije MW. Biochemical, kinetic, and structural characterization of a Bacillus tequilensis nitroreductase. FEBS J 2024. [PMID: 38946302 DOI: 10.1111/febs.17210] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2024] [Revised: 05/17/2024] [Accepted: 06/14/2024] [Indexed: 07/02/2024]
Abstract
Nitroreductases (NRs) are NAD(P)H-dependent flavoenzymes that reduce nitro aromatic compounds to their corresponding arylamines via the nitroso and hydroxylamine intermediates. Because of their broad substrate scope and versatility, NRs have found application in multiple fields such as biocatalysis, bioremediation, cell-imaging and prodrug activation. However, only a limited number of members of the broad NR superfamily (> 24 000 sequences) have been experimentally characterized. Within this group of enzymes, only few are capable of amine synthesis, which is a fundamental chemical transformation for the pharmaceutical, agricultural, and textile industries. Herein, we provide a comprehensive description of a recently discovered NR from Bacillus tequilensis, named BtNR. This enzyme has previously been demonstrated to have the capability to fully convert nitro aromatic and heterocyclic compounds to their respective primary amines. In this study, we determined its biochemical, kinetic and structural properties, including its apparent melting temperature (Tm) of 59 °C, broad pH activity range (from pH 3 to 10) and a notably low redox potential (-236 ± 1 mV) in comparison to other well-known NRs. We also determined its steady-state and pre-steady-state kinetic parameters, which are consistent with other NRs. Additionally, we elucidated the crystal structure of BtNR, which resembles the well-characterized Escherichia coli oxygen-insensitive NAD(P)H nitroreductase (NfsB), and investigated the substrate binding in its active site through docking and molecular dynamics studies with four nitro aromatic substrates. Guided by these structural analyses, we probed the functional roles of active site residues by site-directed mutagenesis. Our findings provide valuable insights into the biochemical and structural properties of BtNR, as well as its potential applications in biotechnology.
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Affiliation(s)
- Sara Russo
- Molecular Enzymology Group, University of Groningen, The Netherlands
- Department of Chemical and Pharmaceutical Biology, University of Groningen, The Netherlands
| | | | - Hein J Wijma
- Molecular Enzymology Group, University of Groningen, The Netherlands
| | - Gerrit J Poelarends
- Department of Chemical and Pharmaceutical Biology, University of Groningen, The Netherlands
| | - Marco W Fraaije
- Molecular Enzymology Group, University of Groningen, The Netherlands
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2
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García de Fuentes A, Möglich A. Reduction midpoint potential of a paradigm light-oxygen-voltage receptor and its modulation by methionine residues. RSC Chem Biol 2024; 5:530-543. [PMID: 38846079 PMCID: PMC11151830 DOI: 10.1039/d4cb00056k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2024] [Accepted: 04/08/2024] [Indexed: 06/09/2024] Open
Abstract
Light-dependent adaptations of organismal physiology, development, and behavior abound in nature and depend on sensory photoreceptors. As one class, light-oxygen-voltage (LOV) photoreceptors harness flavin-nucleotide chromophores to sense blue light. Photon absorption drives the LOV receptor to its signaling state, characterized by a metastable thioadduct between the flavin and a conserved cysteine residue. With this cysteine absent, LOV receptors instead undergo photoreduction to the flavin semiquinone which however can still elicit downstream physiological responses. Irrespective of the cysteine presence, the LOV photochemical response thus entails a formal reduction of the flavin. Against this backdrop, we here investigate the reduction midpoint potential E 0 in the paradigmatic LOV2 domain from Avena sativa phototropin 1 (AsLOV2), and how it can be deliberately varied. Replacements of residues at different sites near the flavin by methionine consistently increase E 0 from its value of around -280 mV by up to 40 mV. Moreover, methionine introduction invariably impairs photoactivation efficiency and thus renders the resultant AsLOV2 variants less light-sensitive. Although individual methionine substitutions also affect the stability of the signaling state and downstream allosteric responses, no clear-cut correlation with the redox properties emerges. With a reduction midpoint potential near -280 mV, AsLOV2 and, by inference, other LOV receptors may be partially reduced inside cells which directly affects their light responsiveness. The targeted modification of the chromophore environment, as presently demonstrated, may mitigate this effect and enables the design of LOV receptors with stratified redox sensitivities.
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Affiliation(s)
| | - Andreas Möglich
- Department of Biochemistry, University of Bayreuth 95447 Bayreuth Germany
- Bayreuth Center for Biochemistry & Molecular Biology, Universität Bayreuth 95447 Bayreuth Germany
- North-Bavarian NMR Center, Universität Bayreuth 95447 Bayreuth Germany
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3
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Tong Y, Rozeboom HJ, Loonstra MR, Wijma HJ, Fraaije MW. Characterization of two bacterial multi-flavinylated proteins harboring multiple covalent flavin cofactors. BBA ADVANCES 2023; 4:100097. [PMID: 37455753 PMCID: PMC10339131 DOI: 10.1016/j.bbadva.2023.100097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2023] [Revised: 06/27/2023] [Accepted: 07/03/2023] [Indexed: 07/18/2023] Open
Abstract
In recent years, studies have shown that a large number of bacteria secrete multi-flavinylated proteins. The exact roles and properties, of these extracellular flavoproteins that contain multiple covalently anchored FMN cofactors, are still largely unknown. Herein, we describe the biochemical and structural characterization of two multi-FMN-containing covalent flavoproteins, SaFMN3 from Streptomyces azureus and CbFMN4 from Clostridiaceae bacterium. Based on their primary structure, these proteins were predicted to contain three and four covalently tethered FMN cofactors, respectively. The genes encoding SaFMN3 and CbFMN4 were heterologously coexpressed with a flavin transferase (ApbE) in Escherichia coli, and could be purified by affinity chromatography in good yields. Both proteins were found to be soluble and to contain covalently bound FMN molecules. The SaFMN3 protein was studied in more detail and found to display a single redox potential (-184 mV) while harboring three covalently attached flavins. This is in line with the high sequence similarity when the domains of each flavoprotein are compared. The fully reduced form of SaFMN3 is able to use dioxygen as electron acceptor. Single domains from both proteins were expressed, purified and crystallized. The crystal structures were elucidated, which confirmed that the flavin cofactor is covalently attached to a threonine. Comparison of both crystal structures revealed a high similarity, even in the flavin binding pocket. Based on the crystal structure, mutants of the SaFMN3-D2 domain were designed to improve its fluorescence quantum yield by changing the microenvironment of the isoalloxazine moiety of the flavin cofactor. Residues that quench the flavin fluorescence were successfully identified. Our study reveals biochemical details of multi-FMN-containing proteins, contributing to a better understanding of their role in bacteria and providing leads to future utilization of these flavoprotein in biotechnology.
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4
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Wijayanti SD, Schachinger F, Ludwig R, Haltrich D. Electrochemical and biosensing properties of an FAD-dependent glucose dehydrogenase from Trichoderma virens. Bioelectrochemistry 2023; 153:108480. [PMID: 37269684 DOI: 10.1016/j.bioelechem.2023.108480] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2023] [Revised: 05/20/2023] [Accepted: 05/24/2023] [Indexed: 06/05/2023]
Abstract
We investigated the bioelectrochemical properties of an FAD-dependent glucose dehydrogenase from Trichoderma virens (TvGDH) and its electrochemical behaviour when immobilized on a graphite electrode. TvGDH was recently shown to have an unusual substrate spectrum and to prefer maltose over glucose as substrate, and hence could be of interest as recognition element in a maltose sensor. In this study, we determined the redox potential of TvGDH, which is -0.268 ± 0.007 V vs. SHE, and advantageously low to be used with many redox mediators or redox polymers. The enzyme was entrapped in, and wired by an osmium redox polymer (poly(1-vinylimidazole-co-allylamine)-{[Os(2,2'-bipyridine)2Cl]Cl}) with formal redox potential of +0.275 V vs. Ag|AgCl via poly(ethylene glycol) diglycidyl ether crosslinking onto a graphite electrode. When the TvGDH-based biosensor was tested with maltose it showed a sensitivity of 1.7 μA mM-1cm-2, a linear range of 0.5-15 mM, and a detection limit of 0.45 mM. Furthermore, it gave the lowest apparent Michaelis-Menten constant (KM app) of 19.2 ± 1.5 mM towards maltose when compared to other sugars. The biosensor is also able to detect other saccharides including glucose, maltotriose and galactose, these however also interfere with maltose sensing.
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Affiliation(s)
- Sudarma Dita Wijayanti
- Department of Food Science and Technology, BOKU - University of Natural Resources and Life Sciences Vienna, Muthgasse 11, A-1190 Wien, Austria; Department of Food Science and Biotechnology, Brawijaya University, Veteran, 65145 Malang, East Java, Indonesia
| | - Franziska Schachinger
- Department of Food Science and Technology, BOKU - University of Natural Resources and Life Sciences Vienna, Muthgasse 11, A-1190 Wien, Austria
| | - Roland Ludwig
- Department of Food Science and Technology, BOKU - University of Natural Resources and Life Sciences Vienna, Muthgasse 11, A-1190 Wien, Austria
| | - Dietmar Haltrich
- Department of Food Science and Technology, BOKU - University of Natural Resources and Life Sciences Vienna, Muthgasse 11, A-1190 Wien, Austria.
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5
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The Differing Roles of Flavins and Quinones in Extracellular Electron Transfer in Lactiplantibacillus plantarum. Appl Environ Microbiol 2023; 89:e0131322. [PMID: 36533923 PMCID: PMC9888254 DOI: 10.1128/aem.01313-22] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Lactiplantibacillus plantarum is a lactic acid bacterium that is commonly found in the human gut and fermented food products. Despite its overwhelmingly fermentative metabolism, this microbe can perform extracellular electron transfer (EET) when provided with an exogenous quinone, 1,4-dihydroxy-2-naphthoic acid (DHNA), and riboflavin. However, the separate roles of DHNA and riboflavin in EET in L. plantarum have remained unclear. Here, we seek to understand the role of quinones and flavins in EET by monitoring iron and anode reduction in the presence and absence of these small molecules. We found that addition of either DHNA or riboflavin can support robust iron reduction, indicating electron transfer to extracellular iron occurs through both flavin-dependent and DHNA-dependent routes. Using genetic mutants of L. plantarum, we found that flavin-dependent iron reduction requires Ndh2 and EetA, while DHNA-dependent iron reduction largely relies on Ndh2 and PplA. In contrast to iron reduction, DHNA-containing medium supported more robust anode reduction than riboflavin-containing medium, suggesting electron transfer to an anode proceeds most efficiently through the DHNA-dependent pathway. Furthermore, we found that flavin-dependent anode reduction requires EetA, Ndh2, and PplA, while DHNA-dependent anode reduction requires Ndh2 and PplA. Taken together, we identify multiple EET routes utilized by L. plantarum and show that the EET route depends on access to environmental biomolecules and on the electron acceptor. This work expands our molecular-level understanding of EET in Gram-positive microbes and provides additional opportunities to manipulate EET for biotechnology. IMPORTANCE Lactic acid bacteria are named because of their nearly exclusive fermentative metabolism. Thus, the recent observation of EET activity-typically associated with anaerobic respiration-in this class of organisms has forced researchers to rethink the rules governing microbial metabolic strategies. Our identification of multiple routes for EET in L. plantarum that depend on two different redox active small molecules expands our understanding of how microbes metabolically adapt to different environments to gain an energetic edge and how these processes can be manipulated for biotechnological uses. Understanding the role of EET in lactic acid bacteria is of great importance due to the significance of lactic acid bacteria in agriculture, bioremediation, food production, and gut health. Furthermore, the maintenance of multiple EET routes speaks to the importance of this process to function under a variety of environmental conditions.
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6
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Van Galen CJ, Pauszek RF, Koder RL, Stanley RJ. Flavin Charge Redistribution upon Optical Excitation Is Independent of Solvent Polarity. J Phys Chem B 2023; 127:661-672. [PMID: 36649202 DOI: 10.1021/acs.jpcb.2c07266] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Flavin absorption spectra encode molecular details of the flavin's local environment through coupling of local electric fields with the chromophore's charge redistribution upon optical excitation. Translating experimentally measured field-tuned transition energies to local electric field magnitudes and directions across a wide range of field magnitudes requires that the charge redistribution be independent of the local field. We have measured the charge redistribution upon optical excitation of the derivatized flavin TPARF in the non-hydrogen-bonding, nonpolar solvent toluene, with and without a tridentate hydrogen-bonding ligand, DBAP, using electronic Stark spectroscopy. These measurements were interpreted using TD-DFT finite field and difference density calculations. In comparing our present results to previous Stark spectroscopic analyses of flavin in more polar solvents, we conclude that flavin charge redistribution upon optical excitation is independent of solvent polarity, indicating that dependence of flavin transition energies on local field magnitude is linear with local field magnitude.
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Affiliation(s)
- Cornelius J Van Galen
- Department of Chemistry, Temple University, 1901 N. 13th St., 250B Beury Hall, Philadelphia, Pennsylvania19122, United States
| | - Raymond F Pauszek
- Department of Chemistry, Temple University, 1901 N. 13th St., 250B Beury Hall, Philadelphia, Pennsylvania19122, United States
| | - Ronald L Koder
- Department of Physics, The City College of New York, 1.308 CDI Bldg., 85 St. Nicholas Terrace, New York, New York10031, United States
| | - Robert J Stanley
- Department of Chemistry, Temple University, 1901 N. 13th St., 250B Beury Hall, Philadelphia, Pennsylvania19122, United States
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7
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The Extracellular Electron Transport Pathway Reduces Copper for Sensing by the CopRS Two-Component System under Anaerobic Conditions in Listeria monocytogenes. J Bacteriol 2023; 205:e0039122. [PMID: 36622231 PMCID: PMC9879103 DOI: 10.1128/jb.00391-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The renowned antimicrobial activity of copper stems in part from its ability to undergo redox cycling between Cu1+/2+ oxidation states. Bacteria counter copper toxicity with a network of sensors that often include two-component signaling systems to direct transcriptional responses. As in typical two-component systems, ligand binding by the extracellular domain of the membrane bound copper sensor component leads to phosphorylation and activation of the cognate response regulator transcription factor. In Listeria monocytogenes, the plasmid-borne CopRS two-component system upregulates both copper resistance and lipoprotein remodeling genes upon copper challenge, but the oxidation state of copper bound by CopS is unknown. Herein, we show CopS utilizes a triad of key residues (His-His-Phe) that are predicted to be at the dimerization interface and that are analogous with the Escherichia coli CusS copper sensor to specifically bind Cu1+/Ag1+ and activate CopR transcription. We demonstrate Cu2+ only induces CopRS if first reduced by electron transport systems, as strains lacking menaquinone carriers were unable to respond to Cu2+. The flavin-dependent extracellular electron transport system (EET) was the main mechanism for metal reduction, capable of either generating inducing ligand (Cu2+ to Cu1+) or removing it by precipitation (Ag1+ to Ag0). We show that EET flux is directly proportional to the rate of Cu2+ reduction and that since EET activity is low under oxygenated conditions when a competing respiratory chain is operating, CopRS signaling in turn is activated only under anaerobic conditions. EET metal reduction thus sensitizes cells to copper while providing resistance to silver under anaerobic growth. IMPORTANCE Two-component extracellular copper sensing from the periplasm of Gram-negative bacteria has been well studied, but copper detection at the cell surface of the Gram-positive L. monocytogenes is less understood. Collectively, our results show that EET is most active under anaerobic conditions and reduces Cu2+ and Ag1+ to, respectively, generate or remove the monovalent ligands that directly bind to CopS and lead to the induction of lipoprotein remodeling genes. This reducing activity regulates CopRS signaling and links the upregulation of copper resistance genes with increasing EET flux. Our studies provide insight into how a two-component copper sensing system is integrated into a model monoderm Firmicute to take cues from the electron transport chain activity.
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8
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Schachinger F, Ma S, Ludwig R. Redox potential of FAD-dependent glucose dehydrogenase. Electrochem commun 2022. [DOI: 10.1016/j.elecom.2022.107405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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9
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Boverio A, Widodo WS, Santema LL, Rozeboom H, Xiang R, Guallar V, Mattevi A, Fraaije MW. Structural Elucidation and Engineering of a Bacterial Carbohydrate Oxidase. Biochemistry 2022; 62:429-436. [PMID: 35881507 PMCID: PMC9850908 DOI: 10.1021/acs.biochem.2c00307] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Flavin-dependent carbohydrate oxidases are valuable tools in biotechnological applications due to their high selectivity in the oxidation of carbohydrates. In this study, we report the biochemical and structural characterization of a recently discovered carbohydrate oxidase from the bacterium Ralstonia solanacearum, which is a member of the vanillyl alcohol oxidase flavoprotein family. Due to its exceptionally high activity toward N-acetyl-d-galactosamine and N-acetyl-d-glucosamine, the enzyme was named N-acetyl-glucosamine oxidase (NagOx). In contrast to most known (fungal) carbohydrate oxidases, NagOx could be overexpressed in a bacterial host, which facilitated detailed biochemical and enzyme engineering studies. Steady state kinetic analyses revealed that non-acetylated hexoses were also accepted as substrates albeit with lower efficiency. Upon determination of the crystal structure, structural insights into NagOx were obtained. A large cavity containing a bicovalently bound FAD, tethered via histidyl and cysteinyl linkages, was observed. Substrate docking highlighted how a single residue (Leu251) plays a key role in the accommodation of N-acetylated sugars in the active site. Upon replacement of Leu251 (L251R mutant), an enzyme variant was generated with a drastically modified substrate acceptance profile, tuned toward non-N-acetylated monosaccharides and disaccharides. Furthermore, the activity toward bulkier substrates such as the trisaccharide maltotriose was introduced by this mutation. Due to its advantage of being overexpressed in a bacterial host, NagOx can be considered a promising alternative engineerable biocatalyst for selective oxidation of monosaccharides and oligosaccharides.
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Affiliation(s)
- Alessandro Boverio
- Molecular
Enzymology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747AG Groningen, The Netherlands,Department
of Biology and Biotechnology, University
of Pavia, via Ferrata 9, 27100 Pavia, Italy
| | - Wahyu S. Widodo
- Molecular
Enzymology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747AG Groningen, The Netherlands
| | - Lars L. Santema
- Molecular
Enzymology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747AG Groningen, The Netherlands
| | - Henriëtte
J. Rozeboom
- Molecular
Enzymology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747AG Groningen, The Netherlands
| | - Ruite Xiang
- Electronic
and Atomic Protein Modelling Group, Barcelona
Supercomputing Center, E-08034 Barcelona, Spain
| | - Víctor Guallar
- Electronic
and Atomic Protein Modelling Group, Barcelona
Supercomputing Center, E-08034 Barcelona, Spain
| | - Andrea Mattevi
- Department
of Biology and Biotechnology, University
of Pavia, via Ferrata 9, 27100 Pavia, Italy
| | - Marco W. Fraaije
- Molecular
Enzymology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747AG Groningen, The Netherlands,
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10
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Tong Y, Loonstra MR, Fraaije M. Broadening the scope of the Flavin-tag method by improving flavin incorporation and incorporating flavin analogs. Chembiochem 2022; 23:e202200144. [PMID: 35373879 PMCID: PMC9400968 DOI: 10.1002/cbic.202200144] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2022] [Revised: 04/01/2022] [Indexed: 11/10/2022]
Abstract
Methods for facile site-selective modifications of proteins are in high demand. We have recently shown that a flavin transferase can be used for site-specific covalent attachment of a chromo- and fluorogenic flavin (FMN) to any targeted protein. Although this Flavin-tag method resulted in efficient labeling of proteins in vitro , labelling in E. coli cells resulted in partial flavin incorporation. It was also restricted in the type of installed label with only type of flavin, FMN, being incorporated. Here, we report on an extension of the Flavin-tag method that addresses previous limitations. We demonstrate that coexpression of FAD synthetase improves the flavin incorporation efficiency, allowing complete flavin-labeling of a target protein in E. coli cells. Furthermore, we have found that various flavin derivatives and even a nicotinamide can be covalently attached to a target protein, rendering this method even more versatile and valuable.
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Affiliation(s)
- Yapei Tong
- University of Groningen: Rijksuniversiteit Groningen, Molecular Enzymology, NETHERLANDS
| | - Marnix R Loonstra
- University of Groningen: Rijksuniversiteit Groningen, Molecular Enzymology, NETHERLANDS
| | - Marco Fraaije
- University of Groningen, Molecular Enzymology group, Nijenborgh 4, 9747AG, Groningen, NETHERLANDS
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11
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Samuelian JS, Gremminger TJ, Song Z, Poudyal RR, Li J, Zhou Y, Staller SA, Carballo JA, Roychowdhury-Saha M, Chen SJ, Burke DH, Heng X, Baum DA. An RNA aptamer that shifts the reduction potential of metabolic cofactors. Nat Chem Biol 2022; 18:1263-1269. [PMID: 36097297 PMCID: PMC9596375 DOI: 10.1038/s41589-022-01121-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Accepted: 07/25/2022] [Indexed: 01/19/2023]
Abstract
The discovery of ribozymes has inspired exploration of RNA's potential to serve as primordial catalysts in a hypothesized RNA world. Modern oxidoreductase enzymes employ differential binding between reduced and oxidized forms of redox cofactors to alter cofactor reduction potential and enhance the enzyme's catalytic capabilities. The utility of differential affinity has been underexplored as a chemical strategy for RNA. Here we show an RNA aptamer that preferentially binds oxidized forms of flavin over reduced forms and markedly shifts flavin reduction potential by -40 mV, similar to shifts for oxidoreductases. Nuclear magnetic resonance structural analysis revealed π-π and donor atom-π interactions between the aptamer and flavin that cause unfavorable contacts with the electron-rich reduced form, suggesting a mechanism by which the local environment of the RNA-binding pocket drives the observed shift in cofactor reduction potential. It seems likely that primordial RNAs could have used similar strategies in RNA world metabolisms.
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Affiliation(s)
- John S. Samuelian
- grid.262962.b0000 0004 1936 9342Department of Chemistry, Saint Louis University, St. Louis, MO USA
| | - Thomas J. Gremminger
- grid.134936.a0000 0001 2162 3504Department of Biochemistry, University of Missouri, Columbia, MO USA ,Present Address: KCAS, LLC, Shawnee, KS USA
| | - Zhenwei Song
- grid.134936.a0000 0001 2162 3504Department of Biochemistry, University of Missouri, Columbia, MO USA
| | - Raghav R. Poudyal
- grid.134936.a0000 0001 2162 3504Department of Biochemistry, University of Missouri, Columbia, MO USA ,grid.134936.a0000 0001 2162 3504Bond Life Sciences Center, University of Missouri, Columbia, MO USA ,grid.410513.20000 0000 8800 7493Present Address: Pfizer, Biomedicine Design, Cambridge, MA USA
| | - Jun Li
- grid.134936.a0000 0001 2162 3504Department of Physics, University of Missouri, Columbia, MO USA
| | - Yuanzhe Zhou
- grid.134936.a0000 0001 2162 3504Department of Physics, University of Missouri, Columbia, MO USA
| | - Seth A. Staller
- grid.134936.a0000 0001 2162 3504Department of Biochemistry, University of Missouri, Columbia, MO USA ,Present Address: Laronde, Inc., Cambridge, MA USA
| | - Johan A. Carballo
- grid.262962.b0000 0004 1936 9342Department of Chemistry, Saint Louis University, St. Louis, MO USA
| | - Manami Roychowdhury-Saha
- grid.411377.70000 0001 0790 959XDepartment of Chemistry, Indiana University, Bloomington, IN USA ,grid.505809.10000 0004 5998 7997Present Address: GRAIL, Menlo Park, CA USA
| | - Shi-Jie Chen
- grid.134936.a0000 0001 2162 3504Department of Biochemistry, University of Missouri, Columbia, MO USA ,grid.134936.a0000 0001 2162 3504Department of Physics, University of Missouri, Columbia, MO USA ,grid.134936.a0000 0001 2162 3504Institute for Data Science and Informatics, University of Missouri, Columbia, MO USA
| | - Donald H. Burke
- grid.134936.a0000 0001 2162 3504Department of Biochemistry, University of Missouri, Columbia, MO USA ,grid.134936.a0000 0001 2162 3504Bond Life Sciences Center, University of Missouri, Columbia, MO USA ,grid.134936.a0000 0001 2162 3504Department of Biological Engineering, University of Missouri, Columbia, MO USA ,grid.134936.a0000 0001 2162 3504Department of Molecular Microbiology and Immunology, University of Missouri, Columbia, MO USA
| | - Xiao Heng
- grid.134936.a0000 0001 2162 3504Department of Biochemistry, University of Missouri, Columbia, MO USA
| | - Dana A. Baum
- grid.262962.b0000 0004 1936 9342Department of Chemistry, Saint Louis University, St. Louis, MO USA
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12
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Structural Features of Cytochrome b5–Cytochrome b5 Reductase Complex Formation and Implications for the Intramolecular Dynamics of Cytochrome b5 Reductase. Int J Mol Sci 2021; 23:ijms23010118. [PMID: 35008543 PMCID: PMC8745658 DOI: 10.3390/ijms23010118] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2021] [Revised: 12/10/2021] [Accepted: 12/21/2021] [Indexed: 12/15/2022] Open
Abstract
Membrane cytochrome b5 reductase is a pleiotropic oxidoreductase that uses primarily soluble reduced nicotinamide adenine dinucleotide (NADH) as an electron donor to reduce multiple biological acceptors localized in cellular membranes. Some of the biological acceptors of the reductase and coupled redox proteins might eventually transfer electrons to oxygen to form reactive oxygen species. Additionally, an inefficient electron transfer to redox acceptors can lead to electron uncoupling and superoxide anion formation by the reductase. Many efforts have been made to characterize the involved catalytic domains in the electron transfer from the reduced flavoprotein to its electron acceptors, such as cytochrome b5, through a detailed description of the flavin and NADH-binding sites. This information might help to understand better the processes and modifications involved in reactive oxygen formation by the cytochrome b5 reductase. Nevertheless, more than half a century since this enzyme was first purified, the one-electron transfer process toward potential electron acceptors of the reductase is still only partially understood. New advances in computational analysis of protein structures allow predicting the intramolecular protein dynamics, identifying potential functional sites, or evaluating the effects of microenvironment changes in protein structure and dynamics. We applied this approach to characterize further the roles of amino acid domains within cytochrome b5 reductase structure, part of the catalytic domain, and several sensors and structural domains involved in the interactions with cytochrome b5 and other electron acceptors. The computational analysis results allowed us to rationalize some of the available spectroscopic data regarding ligand-induced conformational changes leading to an increase in the flavin adenine dinucleotide (FAD) solvent-exposed surface, which has been previously correlated with the formation of complexes with electron acceptors.
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13
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Tararina MA, Dam KK, Dhingra M, Janda KD, Palfey BA, Allen KN. Fast Kinetics Reveals Rate-Limiting Oxidation and the Role of the Aromatic Cage in the Mechanism of the Nicotine-Degrading Enzyme NicA2. Biochemistry 2021; 60:259-273. [PMID: 33464876 DOI: 10.1021/acs.biochem.0c00855] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In Pseudomonas putida, the flavoprotein nicotine oxidoreductase (NicA2) catalyzes the oxidation of (S)-nicotine to N-methyl-myosmine, which is nonenzymatically hydrolyzed to pseudooxynicotine. Structural analysis reveals a monoamine oxidase (MAO)-like fold with a conserved FAD-binding domain and variable substrate-binding domain. The flavoenzyme has a unique variation of the classic aromatic cage with flanking residue pair W427/N462. Previous mechanistic studies using O2 as the oxidizing substrate show that NicA2 has a low apparent Km of 114 nM for (S)-nicotine with a very low apparent turnover number (kcat of 0.006 s-1). Herein, the mechanism of NicA2 was analyzed by transient kinetics. Single-site variants of W427 and N462 were used to probe the roles of these residues. Although several variants had moderately higher oxidase activity (7-12-fold), their reductive half-reactions using (S)-nicotine were generally significantly slower than that of wild-type NicA2. Notably, the reductive half-reaction of wild-type NicA2 is 5 orders of magnitude faster than the oxidative half-reaction with an apparent pseudo-first-order rate constant for the reaction of oxygen similar to kcat. X-ray crystal structures of the N462V and N462Y/W427Y variants complexed with (S)-nicotine (at 2.7 and 2.3 Å resolution, respectively) revealed no significant active-site rearrangements. A second substrate-binding site was identified in N462Y/W427Y, consistent with observed substrate inhibition. Together, these findings elucidate the mechanism of a flavoenzyme that preferentially oxidizes tertiary amines with an efficient reductive half-reaction and a very slow oxidative half-reaction when O2 is the oxidizing substrate, suggesting that the true oxidizing agent is unknown.
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Affiliation(s)
- Margarita A Tararina
- Program in Biomolecular Pharmacology, Boston University School of Medicine, 72 East Concord Street, Boston, Massachusetts 02118, United States
| | - Katie K Dam
- Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, United States
| | - Manaswni Dhingra
- Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, United States
| | | | - Bruce A Palfey
- Department of Biological Chemistry, University of Michigan, 5220E MSRB III 1150 West Medical Center Drive, Ann Arbor, Michigan 48109, United States
| | - Karen N Allen
- Program in Biomolecular Pharmacology, Boston University School of Medicine, 72 East Concord Street, Boston, Massachusetts 02118, United States.,Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, United States
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14
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Vinogradov AA, Shimomura M, Kano N, Goto Y, Onaka H, Suga H. Promiscuous Enzymes Cooperate at the Substrate Level En Route to Lactazole A. J Am Chem Soc 2020; 142:13886-13897. [PMID: 32664727 DOI: 10.1021/jacs.0c05541] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Enzymes involved in the biosynthesis of ribosomally synthesized and post-translationally modified peptides (RiPPs) often have relaxed specificity profiles and are able to modify diverse substrates. When several such enzymes act together during precursor peptide maturation, a multitude of products can form, yet usually the biosynthesis converges on a single natural product. For the most part, the mechanisms controlling the integrity of RiPP assembly remain elusive. Here, we investigate the biosynthesis of lactazole A, a model thiopeptide produced by five promiscuous enzymes from a ribosomal precursor peptide. Using our in vitro thiopeptide production (FIT-Laz) system, we determine the order of biosynthetic events at the individual modification level and supplement this study with substrate scope analysis for participating enzymes. Our results reveal an unusual but well-defined assembly process where cyclodehydration, dehydroalanine formation, and azoline dehydrogenation events are intertwined due to minimal substrate recognition requirements characteristic of every lactazole enzyme. Additionally, each enzyme plays a role in directing LazBF-mediated dehydroalanine formation, which emerges as the central theme of the assembly process. Cyclodehydratase LazDE discriminates a single serine residue for azoline formation, leaving the remaining five as potential dehydratase substrates. Pyridine synthase LazC exerts kinetic control over LazBF to prevent the formation of overdehydrated thiopeptides, whereas the coupling of dehydrogenation to dehydroalanine installation impedes generation of underdehydrated products. Altogether, our results indicate that substrate-level cooperation between the biosynthetic enzymes maintains the integrity of lactazole assembly. This work advances our understanding of RiPP biosynthesis processes and facilitates thiopeptide bioengineering.
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Affiliation(s)
- Alexander A Vinogradov
- Department of Chemistry, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
| | | | - Naokazu Kano
- Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan
| | - Yuki Goto
- Department of Chemistry, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
| | | | - Hiroaki Suga
- Department of Chemistry, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
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15
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Maklashina E, Cecchini G. Determination of Flavin Potential in Proteins by Xanthine/Xanthine Oxidase Method. Bio Protoc 2020; 10:e3571. [PMID: 33659541 DOI: 10.21769/bioprotoc.3571] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 02/25/2020] [Accepted: 02/26/2020] [Indexed: 11/02/2022] Open
Abstract
This protocol describes a simple xanthine/xanthine oxidase enzymatic equilibration method for determination of the redox potential of a flavin. As an example of the use of this method, we determine the reduction potential of the covalently bound FAD cofactor ( Em = -55 mV) in the SdhA flavoprotein subunit of succinate dehydrogenase from Escherichia coli. In principle, this method can be used routinely to determine the redox potential of flavin cofactors in any simple flavoprotein from equilibrium concentrations with an appropriate reference dye of known Em without the use of sophisticated electrochemical equipment.
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Affiliation(s)
- Elena Maklashina
- Molecular Biology Division, San Francisco VA Health Care System, San Francisco, CA 94121, USA.,Department of Biochemistry & Biophysics, University of California, San Francisco, Ca 95158, USA
| | - Gary Cecchini
- Molecular Biology Division, San Francisco VA Health Care System, San Francisco, CA 94121, USA.,Department of Biochemistry & Biophysics, University of California, San Francisco, Ca 95158, USA
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