1
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Quaye JA, Wood KE, Snelgrove C, Ouedraogo D, Gadda G. An active site mutation induces oxygen reactivity in D-arginine dehydrogenase: A case of superoxide diverting protons. J Biol Chem 2024; 300:107381. [PMID: 38762175 PMCID: PMC11193025 DOI: 10.1016/j.jbc.2024.107381] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2024] [Revised: 05/09/2024] [Accepted: 05/13/2024] [Indexed: 05/20/2024] Open
Abstract
Enzymes are potent catalysts that increase biochemical reaction rates by several orders of magnitude. Flavoproteins are a class of enzymes whose classification relies on their ability to react with molecular oxygen (O2) during catalysis using ionizable active site residues. Pseudomonas aeruginosa D-arginine dehydrogenase (PaDADH) is a flavoprotein that oxidizes D-arginine for P. aeruginosa survival and biofilm formation. The crystal structure of PaDADH reveals the interaction of the glutamate 246 (E246) side chain with the substrate and at least three other active site residues, establishing a hydrogen bond network in the active site. Additionally, E246 likely ionizes to facilitate substrate binding during PaDADH catalysis. This study aimed to investigate how replacing the E246 residue with leucine affects PaDADH catalysis and its ability to react with O2 using steady-state kinetics coupled with pH profile studies. The data reveal a gain of O2 reactivity in the E246L variant, resulting in a reduced flavin semiquinone species and superoxide (O2•-) during substrate oxidation. The O2•- reacts with active site protons, resulting in an observed nonstoichiometric slope of 1.5 in the enzyme's log (kcat/Km) pH profile with D-arginine. Adding superoxide dismutase results in an observed correction of the slope to 1.0. This study demonstrates how O2•- can alter the slopes of limbs in the pH profiles of flavin-dependent enzymes and serves as a model for correcting nonstoichiometric slopes in elucidating reaction mechanisms of flavoproteins.
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Affiliation(s)
- Joanna A Quaye
- Department of Chemistry, Georgia State University, Atlanta, Georgia, USA
| | - Kendall E Wood
- Biology Department, Morehouse College, Atlanta, Georgia, USA
| | - Claire Snelgrove
- The Gwinnett School of Mathematics, Science, and Technology, Lawrenceville, Georgia, USA
| | - Daniel Ouedraogo
- Department of Chemistry, Georgia State University, Atlanta, Georgia, USA
| | - Giovanni Gadda
- Department of Chemistry, Georgia State University, Atlanta, Georgia, USA; Department of Biology, Georgia State University, Atlanta, Georgia, USA; Department of the Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia, USA.
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2
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Quaye J, Ouedraogo D, Gadda G. Targeted Mutation of a Non-catalytic Gating Residue Increases the Rate of Pseudomonas aeruginosa d-Arginine Dehydrogenase Catalytic Turnover. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2023; 71. [PMID: 37933126 PMCID: PMC10655190 DOI: 10.1021/acs.jafc.3c05328] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Revised: 10/11/2023] [Accepted: 10/17/2023] [Indexed: 11/08/2023]
Abstract
Commercial food and l-amino acid industries rely on bioengineered d-amino acid oxidizing enzymes to detect and remove d-amino acid contaminants. However, the bioengineering of enzymes to generate faster biological catalysts has proven difficult as a result of the failure to target specific kinetic steps that limit enzyme turnover, kcat, and the poor understanding of loop dynamics critical for catalysis. Pseudomonas aeruginosa d-arginine dehydrogenase (PaDADH) oxidizes most d-amino acids and is a good candidate for application in the l-amino acid and food industries. The side chain of the loop L2 E246 residue located at the entrance of the PaDADH active site pocket potentially favors the closed active site conformation and secures the substrate upon binding. This study used site-directed mutagenesis, steady-state, and rapid reaction kinetics to generate the glutamine, glycine, and leucine variants and investigate whether increasing the rate of product release could translate to an increased enzyme turnover rate. Upon E246 mutation to glycine, there was an increased rate of d-arginine turnover kcat from 122 to 500 s-1. Likewise, the kcat values increased 2-fold for the glutamine or leucine variants. Thus, we have engineered a faster biocatalyst for industrial applications by selectively increasing the rate of the PaDADH product release.
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Affiliation(s)
- Joanna
Afokai Quaye
- Department
of Chemistry, Georgia State University, Atlanta, Georgia 30302-3965, United
States
| | - Daniel Ouedraogo
- Department
of Chemistry, Georgia State University, Atlanta, Georgia 30302-3965, United
States
| | - Giovanni Gadda
- Department
of Chemistry, Georgia State University, Atlanta, Georgia 30302-3965, United
States
- Department
of Biology, Georgia State University, Atlanta, Georgia 30302-3965, United
States
- Center
for Diagnostics and Therapeutics, Georgia
State University, Atlanta, Georgia 30302-3965, United States
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3
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Yildiz I. Computational Insights on the Hydride and Proton Transfer Mechanisms of D-Arginine Dehydrogenase. Chemphyschem 2023; 24:e202300431. [PMID: 37540527 DOI: 10.1002/cphc.202300431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2023] [Revised: 08/04/2023] [Accepted: 08/04/2023] [Indexed: 08/05/2023]
Abstract
D-Arginine dehydrogenase from Pseudomonas aeruginosa (PaDADH) is an amine oxidase which catalyzes the conversion of D-arginine into iminoarginine. It contains a non-covalent FAD cofactor that is involved in the oxidation mechanism. Based on substrate, solvent, and multiple kinetic isotope effects studies, a stepwise hydride transfer mechanism is proposed. It was shown that D-arginine binds to the active site of enzyme as α-amino group protonated, and it is deprotonated before a hydride ion is transferred from its α-C to FAD. Based on a mutagenesis study, it was concluded that a water molecule is the most likely catalytic base responsible from the deprotonation of α-amino group. In this study, we formulated computational models based on ONIOM method to elucidate the oxidation mechanism of D-arginine into iminoarginine using the crystal structure of enzyme complexed with iminoarginine. The calculations showed that Arg222, Arg305, Tyr249, Glu87, His 48, and two active site water molecules play key roles in binding and catalysis. Model systems showed that the deprotonation step occurs prior to hydride transfer step, and active site water molecule(s) may have participated in the deprotonation process.
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Affiliation(s)
- Ibrahim Yildiz
- Khalifa University, Chemistry Department and Applied Material Chemistry Center (AMCC), PO Box, 127788, Abu Dhabi, UAE
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4
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Moni BM, Quaye JA, Gadda G. Mutation of a distal gating residue modulates NADH binding in NADH:Quinone oxidoreductase from Pseudomonas aeruginosa PAO1. J Biol Chem 2023; 299:103044. [PMID: 36803963 PMCID: PMC10033279 DOI: 10.1016/j.jbc.2023.103044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2022] [Revised: 02/07/2023] [Accepted: 02/11/2023] [Indexed: 02/19/2023] Open
Abstract
Enzymes require flexible regions to adopt multiple conformations during catalysis. The mobile regions of enzymes include gates that modulate the passage of molecules in and out of the enzyme's active site. The enzyme PA1024 from Pseudomonas aeruginosa PA01 is a recently discovered flavin-dependent NADH:quinone oxidoreductase (NQO, EC 1.6.5.9). Q80 in loop 3 (residues 75-86) of NQO is ∼15 Å away from the flavin and creates a gate that seals the active site through a hydrogen bond with Y261 upon NADH binding. In this study, we mutated Q80 to glycine, leucine, or glutamate to investigate the mechanistic significance of distal residue Q80 in NADH binding in the active site of NQO. The UV-visible absorption spectrum reveals that the mutation of Q80 minimally affects the protein microenvironment surrounding the flavin. The anaerobic reductive half-reaction of the NQO-mutants yields a ≥25-fold increase in the Kd value for NADH compared to the WT enzyme. However, we determined that the kred value was similar in the Q80G, Q80L, and wildtype enzymes and only ∼25% smaller in the Q80E enzyme. Steady-state kinetics with NQO-mutants and NQO-WT at varying concentrations of NADH and 1,4-benzoquinone establish a ≤5-fold decrease in the kcat/KNADH value. Moreover, there is no significant difference in the kcat/KBQ (∼1 × 106 M-1s-1) and kcat (∼24 s-1) values in NQO-mutants and NQO-WT. These results are consistent with the distal residue Q80 being mechanistically essential for NADH binding to NQO with minimal effect on the quinone binding to the enzyme and hydride transfer from NADH to flavin.
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Affiliation(s)
- Bilkis Mehrin Moni
- Department of Chemistry, Georgia State University, Atlanta, Georgia, USA
| | - Joanna A Quaye
- Department of Chemistry, Georgia State University, Atlanta, Georgia, USA
| | - Giovanni Gadda
- Department of Chemistry, Georgia State University, Atlanta, Georgia, USA; Department of Biology, Georgia State University, Atlanta, Georgia, USA; The Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia, USA.
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5
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Ouedraogo D, Souffrant M, Yao XQ, Hamelberg D, Gadda G. Non-active Site Residue in Loop L4 Alters Substrate Capture and Product Release in d-Arginine Dehydrogenase. Biochemistry 2023; 62:1070-1081. [PMID: 36795942 PMCID: PMC9996824 DOI: 10.1021/acs.biochem.2c00697] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Abstract
Numerous studies demonstrate that enzymes undergo multiple conformational changes during catalysis. The malleability of enzymes forms the basis for allosteric regulation: residues located far from the active site can exert long-range dynamical effects on the active site residues to modulate catalysis. The structure of Pseudomonas aeruginosa d-arginine dehydrogenase (PaDADH) shows four loops (L1, L2, L3, and L4) that span the substrate and the FAD-binding domains. Loop L4 comprises residues 329-336, spanning over the flavin cofactor. The I335 residue on loop L4 is ∼10 Å away from the active site and ∼3.8 Å from N(1)-C(2)═O atoms of the flavin. In this study, we used molecular dynamics and biochemical techniques to investigate the effect of the mutation of I335 to histidine on the catalytic function of PaDADH. Molecular dynamics showed that the conformational dynamics of PaDADH are shifted to a more closed conformation in the I335H variant. In agreement with an enzyme that samples more in a closed conformation, the kinetic data of the I335H variant showed a 40-fold decrease in the rate constant of substrate association (k1), a 340-fold reduction in the rate constant of substrate dissociation from the enzyme-substrate complex (k2), and a 24-fold decrease in the rate constant of product release (k5), compared to that of the wild-type. Surprisingly, the kinetic data are consistent with the mutation having a negligible effect on the reactivity of the flavin. Altogether, the data indicate that the residue at position 335 has a long-range dynamical effect on the catalytic function in PaDADH.
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Affiliation(s)
- Daniel Ouedraogo
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States
| | - Michael Souffrant
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States
| | - Xin-Qiu Yao
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States
| | - Donald Hamelberg
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States.,Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia 30302, United States.,Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30302, United States
| | - Giovanni Gadda
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States.,Department of Biology, Georgia State University, Atlanta, Georgia 30302, United States.,Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia 30302, United States.,Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30302, United States
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6
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Iyer A, Reis RAG, Agniswamy J, Weber IT, Gadda G. Discovery of a new flavin N5-adduct in a tyrosine to phenylalanine variant of d-Arginine dehydrogenase. Arch Biochem Biophys 2022; 715:109100. [PMID: 34864048 DOI: 10.1016/j.abb.2021.109100] [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: 10/29/2021] [Revised: 11/29/2021] [Accepted: 11/30/2021] [Indexed: 11/02/2022]
Abstract
d-Arginine dehydrogenase from Pseudomonas aeruginosa (PaDADH) catalyzes the flavin-dependent oxidation of d-arginine and other d-amino acids. Here, we report the crystal structure at 1.29 Å resolution for PaDADH-Y249F expressed and co-crystallized with d-arginine. The overall structure of PaDADH-Y249F resembled PaDADH-WT, but the electron density for the flavin cofactor was ambiguous, suggesting the presence of modified flavins. Electron density maps and mass spectrometric analysis confirmed the presence of both N5-(4-guanidino-oxobutyl)-FAD and 6-OH-FAD in a single crystal of PaDADH-Y249F and helped with the further refinement of the X-ray crystal structure. The versatility of the reduced flavin is apparent in the PaDADH-Y249F structure and is evidenced by the multiple functions it can perform in the same active site.
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Affiliation(s)
- Archana Iyer
- Department of Chemistry, Georgia State University, Atlanta, GA, 30302, USA
| | - Renata A G Reis
- Department of Chemistry, Georgia State University, Atlanta, GA, 30302, USA
| | - Johnson Agniswamy
- Department of Biology, Georgia State University, Atlanta, GA, 30302, USA
| | - Irene T Weber
- Department of Chemistry, Georgia State University, Atlanta, GA, 30302, USA; Department of Biology, Georgia State University, Atlanta, GA, 30302, USA
| | - Giovanni Gadda
- Department of Chemistry, Georgia State University, Atlanta, GA, 30302, USA; Department of Biology, Georgia State University, Atlanta, GA, 30302, USA; Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, GA, 30302, USA.
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7
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Iyer A, Reis RAG, Gannavaram S, Momin M, Spring-Connell AM, Orozco-Gonzalez Y, Agniswamy J, Hamelberg D, Weber IT, Gozem S, Wang S, Germann MW, Gadda G. A Single-Point Mutation in d-Arginine Dehydrogenase Unlocks a Transient Conformational State Resulting in Altered Cofactor Reactivity. Biochemistry 2021; 60:711-724. [PMID: 33630571 DOI: 10.1021/acs.biochem.1c00054] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Proteins are inherently dynamic, and proper enzyme function relies on conformational flexibility. In this study, we demonstrated how an active site residue changes an enzyme's reactivity by modulating fluctuations between conformational states. Replacement of tyrosine 249 (Y249) with phenylalanine in the active site of the flavin-dependent d-arginine dehydrogenase yielded an enzyme with both an active yellow FAD (Y249F-y) and an inactive chemically modified green FAD, identified as 6-OH-FAD (Y249F-g) through various spectroscopic techniques. Structural investigation of Y249F-g and Y249F-y variants by comparison to the wild-type enzyme showed no differences in the overall protein structure and fold. A closer observation of the active site of the Y249F-y enzyme revealed an alternative conformation for some active site residues and the flavin cofactor. Molecular dynamics simulations probed the alternate conformations observed in the Y249F-y enzyme structure and showed that the enzyme variant with FAD samples a metastable conformational state, not available to the wild-type enzyme. Hybrid quantum/molecular mechanical calculations identified differences in flavin electronics between the wild type and the alternate conformation of the Y249F-y enzyme. The computational studies further indicated that the alternate conformation in the Y249F-y enzyme is responsible for the higher spin density at the C6 atom of flavin, which is consistent with the formation of 6-OH-FAD in the variant enzyme. The observations in this study are consistent with an alternate conformational space that results in fine-tuning the microenvironment around a versatile cofactor playing a critical role in enzyme function.
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Affiliation(s)
- Archana Iyer
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States
| | - Renata A G Reis
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States
| | - Swathi Gannavaram
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States
| | - Mohamed Momin
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States
| | | | | | - Johnson Agniswamy
- Department of Biology, Georgia State University, Atlanta, Georgia 30302, United States
| | - Donald Hamelberg
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States
| | - Irene T Weber
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States.,Department of Biology, Georgia State University, Atlanta, Georgia 30302, United States
| | - Samer Gozem
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States
| | - Siming Wang
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States
| | - Markus W Germann
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States.,Department of Biology, Georgia State University, Atlanta, Georgia 30302, United States
| | - Giovanni Gadda
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302, United States.,Department of Biology, Georgia State University, Atlanta, Georgia 30302, United States.,Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia 30302, United States
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8
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Su D, Aguillon C, Gadda G. Characterization of conserved active site residues in class I nitronate monooxygenase. Arch Biochem Biophys 2019; 672:108058. [PMID: 31356775 DOI: 10.1016/j.abb.2019.07.023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2019] [Revised: 07/24/2019] [Accepted: 07/25/2019] [Indexed: 01/08/2023]
Abstract
Propionate 3-nitronate (P3N) is a natural toxin that irreversibly inhibits mitochondrial succinate dehydrogenase. P3N poisoning leads to a variety of neurological disorders and even death. Nitronate monooxygenase (NMO) from Pseudomonas aeruginosa PAO1 was the first NMO characterized in bacteria and serves as a paradigm for Class I NMO. Here, we hypothesized that the carboxylate group of P3N might form a hydrogen bond with one or more of the four tyrosine or a lysine residues that are conserved in the active site of the enzyme. In the wild-type enzyme, the kcat value was pH independent between pH 6.0 and 11.0, while the kcat/KP3N value decreased at high pH, suggesting that a protonated group with a pKa value of 9.5 is required for binding the anionic substrate. A pH titration of the UV-visible absorption spectrum of the enzyme showed an increased absorbance at 297 nm with increasing pH, defining a pKa value of 9.5 and a Δε297 nm of 2.4 M-1cm-1, consistent with a tyrosine being important for substrate binding. The N3 atom of the oxidized flavin, instead, did not ionize likely because its pKa was perturbed by the ionization of a tyrosine in the active site of the enzyme. The Y109F, Y254F, Y299F, Y303F, and K307 M, substitutions had small effects (i.e., <3.5-fold) on the steady-state kinetic parameters of the enzyme. With all mutated enzymes, the kcat/KP3N value was less than 2.5-fold different from the wild-type enzyme, suggesting that none of the residues is solely essential for substrate binding.
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9
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Ball J, Reis RAG, Agniswamy J, Weber IT, Gadda G. Steric hindrance controls pyridine nucleotide specificity of a flavin-dependent NADH:quinone oxidoreductase. Protein Sci 2018; 28:167-175. [PMID: 30246917 DOI: 10.1002/pro.3514] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Revised: 09/12/2018] [Accepted: 09/17/2018] [Indexed: 02/04/2023]
Abstract
The crystal structure of the NADH:quinone oxidoreductase PA1024 has been solved in complex with NAD+ to 2.2 Å resolution. The nicotinamide C4 is 3.6 Å from the FMN N5 atom, with a suitable orientation for facile hydride transfer. NAD+ binds in a folded conformation at the interface of the TIM-barrel domain and the extended domain of the enzyme. Comparison of the enzyme-NAD+ structure with that of the ligand-free enzyme revealed a different conformation of a short loop (75-86) that is part of the NAD+ -binding pocket. P78, P82, and P84 provide internal rigidity to the loop, whereas Q80 serves as an active site latch that secures the NAD+ within the binding pocket. An interrupted helix consisting of two α-helices connected by a small three-residue loop binds the pyrophosphate moiety of NAD+ . The adenine moiety of NAD+ appears to π-π stack with Y261. Steric constraints between the adenosine ribose of NAD+ , P78, and Q80, control the strict specificity of the enzyme for NADH. Charged residues do not play a role in the specificity of PA1024 for the NADH substrate.
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Affiliation(s)
- Jacob Ball
- Department of Chemistry, Georgia State University, Atlanta, Georgia, 30302-3965
| | - Renata A G Reis
- Department of Chemistry, Georgia State University, Atlanta, Georgia, 30302-3965
| | - Johnson Agniswamy
- School of Biology, Centers for Georgia State University, Atlanta, Georgia, 30302-3965
| | - Irene T Weber
- Department of Chemistry, Georgia State University, Atlanta, Georgia, 30302-3965.,School of Biology, Centers for Georgia State University, Atlanta, Georgia, 30302-3965.,Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia, 30302-3965.,Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia, 30302-3965
| | - Giovanni Gadda
- Department of Chemistry, Georgia State University, Atlanta, Georgia, 30302-3965.,School of Biology, Centers for Georgia State University, Atlanta, Georgia, 30302-3965.,Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia, 30302-3965.,Diagnostics and Therapeutics, Georgia State University, Atlanta, Georgia, 30302-3965
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10
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Ball J, Gannavaram S, Gadda G. Structural determinants for substrate specificity of flavoenzymes oxidizing d-amino acids. Arch Biochem Biophys 2018; 660:87-96. [PMID: 30312594 DOI: 10.1016/j.abb.2018.10.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Revised: 10/01/2018] [Accepted: 10/08/2018] [Indexed: 12/26/2022]
Abstract
The oxidation of d-amino acids is relevant to neurodegenerative diseases, detoxification, and nutrition in microorganisms and mammals. It is also important for the resolution of racemic amino acid mixtures and the preparation of chiral building blocks for the pharmaceutical and food industry. Considerable biochemical and structural knowledge has been accrued in recent years on the enzymes that carry out the oxidation of the Cα-N bond of d-amino acids. These enzymes contain FAD as a required coenzyme, share similar overall three-dimensional folds and highly conserved active sites, but differ in their specificity for substrates with neutral, anionic, or cationic side-chains. Here, we summarize the current biochemical and structural knowledge regarding substrate specificity on d-amino acid oxidase, d-aspartate oxidase, and d-arginine dehydrogenase for which a wealth of biochemical and structural studies is available.
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Affiliation(s)
- Jacob Ball
- Departments of Chemistry, Georgia State University, Atlanta, GA, 30302-3965, USA
| | - Swathi Gannavaram
- Departments of Chemistry, Georgia State University, Atlanta, GA, 30302-3965, USA
| | - Giovanni Gadda
- Departments of Chemistry, Georgia State University, Atlanta, GA, 30302-3965, USA; Departments of Biology, Georgia State University, Atlanta, GA, 30302-3965, USA; Center for Biotechnology and Drug Design, Georgia State University, Atlanta, GA, 30302-3965, USA; Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, GA, 30302-3965, USA.
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11
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Ouedraogo D, Ball J, Iyer A, Reis RAG, Vodovoz M, Gadda G. Amine oxidation by d-arginine dehydrogenase in Pseudomonas aeruginosa. Arch Biochem Biophys 2017. [PMID: 28625766 DOI: 10.1016/j.abb.2017.06.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
d-Arginine dehydrogenase from Pseudomonas aeruginosa (PaDADH) is a flavin-dependent oxidoreductase, which is part of a novel two-enzyme racemization system that functions to convert d-arginine to l-arginine. PaDADH contains a noncovalently linked FAD that shows the highest activity with d-arginine. The enzyme exhibits broad substrate specificity towards d-amino acids, particularly with cationic and hydrophobic d-amino acids. Biochemical studies have established the structure and the mechanistic properties of the enzyme. The enzyme is a true dehydrogenase because it displays no reactivity towards molecular oxygen. As established through solvent and multiple kinetic isotope studies, PaDADH catalyzes an asynchronous CH and NH bond cleavage via a hydride transfer mechanism. Steady-state kinetic studies with d-arginine and d-histidine are consistent with the enzyme following a ping-pong bi-bi mechanism. As shown by a combination of crystallography, kinetic and computational data, the shape and flexibility of loop L1 in the active site of PaDADH are important for substrate capture and broad substrate specificity.
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Affiliation(s)
- Daniel Ouedraogo
- Department of Chemistry, Georgia State University, Atlanta, GA 30302, United States
| | - Jacob Ball
- Department of Chemistry, Georgia State University, Atlanta, GA 30302, United States
| | - Archana Iyer
- Department of Chemistry, Georgia State University, Atlanta, GA 30302, United States
| | - Renata A G Reis
- Department of Chemistry, Georgia State University, Atlanta, GA 30302, United States
| | - Maria Vodovoz
- Department of Chemistry, Georgia State University, Atlanta, GA 30302, United States
| | - Giovanni Gadda
- Department of Chemistry, Georgia State University, Atlanta, GA 30302, United States; Department of Biology, Georgia State University, Atlanta, GA 30302, United States; Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, GA 30302, United States; Center for Biotechnology and Drug Design, Georgia State University, Atlanta, GA 30302, United States.
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12
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Ouedraogo D, Souffrant M, Vasquez S, Hamelberg D, Gadda G. Importance of Loop L1 Dynamics for Substrate Capture and Catalysis in Pseudomonas aeruginosa d-Arginine Dehydrogenase. Biochemistry 2017; 56:2477-2487. [DOI: 10.1021/acs.biochem.7b00098] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Daniel Ouedraogo
- Department
of Chemistry, ‡Department of Biology, §Center for Diagnostics and Therapeutics, and ∥Center for Biotechnology
and Drug Design, Georgia State University, Atlanta, Georgia 30302, United States
| | - Michael Souffrant
- Department
of Chemistry, ‡Department of Biology, §Center for Diagnostics and Therapeutics, and ∥Center for Biotechnology
and Drug Design, Georgia State University, Atlanta, Georgia 30302, United States
| | - Sheena Vasquez
- Department
of Chemistry, ‡Department of Biology, §Center for Diagnostics and Therapeutics, and ∥Center for Biotechnology
and Drug Design, Georgia State University, Atlanta, Georgia 30302, United States
| | - Donald Hamelberg
- Department
of Chemistry, ‡Department of Biology, §Center for Diagnostics and Therapeutics, and ∥Center for Biotechnology
and Drug Design, Georgia State University, Atlanta, Georgia 30302, United States
| | - Giovanni Gadda
- Department
of Chemistry, ‡Department of Biology, §Center for Diagnostics and Therapeutics, and ∥Center for Biotechnology
and Drug Design, Georgia State University, Atlanta, Georgia 30302, United States
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13
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The origin of the supernumerary subunits and assembly factors of complex I: A treasure trove of pathway evolution. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:971-9. [PMID: 27048931 DOI: 10.1016/j.bbabio.2016.03.027] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2016] [Revised: 03/16/2016] [Accepted: 03/18/2016] [Indexed: 11/20/2022]
Abstract
We review and document the evolutionary origin of all complex I assembly factors and nine supernumerary subunits from protein families. Based on experimental data and the conservation of critical residues we identify a spectrum of protein function conservation between the complex I representatives and their non-complex I homologs. This spectrum ranges from proteins that have retained their molecular function but in which the substrate specificity may have changed or have become more specific, like NDUFAF5, to proteins that have lost their original molecular function and critical catalytic residues like NDUFAF6. In between are proteins that have retained their molecular function, which however appears unrelated to complex I, like ACAD9, or proteins in which amino acids of the active site are conserved but for which no enzymatic activity has been reported, like NDUFA10. We interpret complex I evolution against the background of molecular evolution theory. Complex I supernumerary subunits and assembly factors appear to have been recruited from proteins that are mitochondrial and/or that are expressed when complex I is active. Within the evolution of complex I and its assembly there are many cases of neofunctionalization after gene duplication, like ACAD9 and TMEM126B, one case of subfunctionalization: ACPM1 and ACPM2 in Yarrowia lipolytica, and one case in which a complex I protein itself appears to have been the source of a new protein from another complex: NDUFS6 gave rise to cytochrome c oxidase subunit COX4/COX5b. Complex I and its assembly can therewith be regarded as a treasure trove for pathway evolution. This article is part of a Special Issue entitled Respiratory complex I, edited by Volker Zickermann and Ulrich Brandt.
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Satomura T, Sakuraba H, Suye SI, Ohshima T. Dye-linked D-amino acid dehydrogenases: biochemical characteristics and applications in biotechnology. Appl Microbiol Biotechnol 2015; 99:9337-47. [PMID: 26362681 DOI: 10.1007/s00253-015-6944-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Revised: 08/12/2015] [Accepted: 08/17/2015] [Indexed: 10/23/2022]
Abstract
Dye-linked D-amino acid dehydrogenases (Dye-DADHs) catalyze the dehydrogenation of free D-amino acids in the presence of an artificial electron acceptor. Although Dye-DADHs functioning in catabolism of L-alanine and as primary enzymes in electron transport chains are widely distributed in mesophilic Gram-negative bacteria, biochemical and biotechnological information on these enzymes remains scanty. This is in large part due to their instability after isolation. On the other hand, in the last decade, several novel types of Dye-DADH have been found in thermophilic bacteria and hyperthermophilic archaea, where they contribute not only to L-alanine catabolism but also to the catabolism of other amino acids, including D-arginine and L-hydroxyproline. In this minireview, we summarize recent developments in our understanding of the biochemical characteristics of Dye-DADHs and their specific application to electrochemical biosensors.
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Affiliation(s)
- Takenori Satomura
- Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui, 910-8507, Japan.
| | - Haruhiko Sakuraba
- Department of Applied Biological Science, Faculty of Agriculture, Kagawa University, 2393 Ikenobe, Miki-cho, Kita-gun, Kagawa, 761-0795, Japan
| | - Shin-Ichiro Suye
- Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui, 910-8507, Japan.,Department of Frontier Fiber Technology and Sciences, Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui, 910-8507, Japan
| | - Toshihisa Ohshima
- Department of Biomedical engineering, Faculty of Engineering, Osaka Institute of Technology, Ohmiya, 5-16-1 Asahi-ku, Ohsaka, 535-8585, Japan
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15
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Ball J, Bui QV, Gannavaram S, Gadda G. Importance of glutamate 87 and the substrate α-amine for the reaction catalyzed by d-arginine dehydrogenase. Arch Biochem Biophys 2015; 568:56-63. [DOI: 10.1016/j.abb.2015.01.017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Revised: 01/16/2015] [Accepted: 01/20/2015] [Indexed: 10/24/2022]
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EQUAR MY, TANI Y, MIHARA H. Purification and Properties of Glycine Oxidase from Pseudomonas putida KT2440. J Nutr Sci Vitaminol (Tokyo) 2015; 61:506-10. [DOI: 10.3177/jnsv.61.506] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
| | - Yasushi TANI
- College of Life Sciences, Ritsumeikan University
- R-GIRO, Ritsumeikan University
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Fitzpatrick PF. Combining solvent isotope effects with substrate isotope effects in mechanistic studies of alcohol and amine oxidation by enzymes. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2014; 1854:1746-55. [PMID: 25448013 DOI: 10.1016/j.bbapap.2014.10.020] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2014] [Revised: 10/17/2014] [Accepted: 10/20/2014] [Indexed: 10/24/2022]
Abstract
Oxidation of alcohols and amines is catalyzed by multiple families of flavin- and pyridine nucleotide-dependent enzymes. Measurement of solvent isotope effects provides a unique mechanistic probe of the timing of the cleavage of the OH and NH bonds, necessary information for a complete description of the catalytic mechanism. The inherent ambiguities in interpretation of solvent isotope effects can be significantly decreased if isotope effects arising from isotopically labeled substrates are measured in combination with solvent isotope effects. The application of combined solvent and substrate (mainly deuterium) isotope effects to multiple enzymes is described here to illustrate the range of mechanistic insights that such an approach can provide. This article is part of a Special Issue entitled: Enzyme Transition States from Theory and Experiment.
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Affiliation(s)
- Paul F Fitzpatrick
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, TX 78212, USA.
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18
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Gannavaram S, Sirin S, Sherman W, Gadda G. Mechanistic and Computational Studies of the Reductive Half-Reaction of Tyrosine to Phenylalanine Active Site Variants of d-Arginine Dehydrogenase. Biochemistry 2014; 53:6574-83. [PMID: 25243743 DOI: 10.1021/bi500917q] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | - Sarah Sirin
- Schrödinger, LLC, 120 West 45st Street, New York, New York 10036, United States
| | - Woody Sherman
- Schrödinger, LLC, 120 West 45st Street, New York, New York 10036, United States
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Li Q, Li M, Ma L, Li W, Wu X, Richards J, Fu G, Xu W, Bythwood T, Li X, Wang J, Song Q. A method to evaluate genome-wide methylation in archival formalin-fixed, paraffin-embedded ovarian epithelial cells. PLoS One 2014; 9:e104481. [PMID: 25133528 PMCID: PMC4136734 DOI: 10.1371/journal.pone.0104481] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Accepted: 07/08/2014] [Indexed: 12/21/2022] Open
Abstract
BACKGROUND The use of DNA from archival formalin and paraffin embedded (FFPE) tissue for genetic and epigenetic analyses may be problematic, since the DNA is often degraded and only limited amounts may be available. Thus, it is currently not known whether genome-wide methylation can be reliably assessed in DNA from archival FFPE tissue. METHODOLOGY/PRINCIPAL FINDINGS Ovarian tissues, which were obtained and formalin-fixed and paraffin-embedded in either 1999 or 2011, were sectioned and stained with hematoxylin-eosin (H&E).Epithelial cells were captured by laser micro dissection, and their DNA subjected to whole genomic bisulfite conversion, whole genomic polymerase chain reaction (PCR) amplification, and purification. Sequencing and software analyses were performed to identify the extent of genomic methylation. We observed that 31.7% of sequence reads from the DNA in the 1999 archival FFPE tissue, and 70.6% of the reads from the 2011 sample, could be matched with the genome. Methylation rates of CpG on the Watson and Crick strands were 32.2% and 45.5%, respectively, in the 1999 sample, and 65.1% and 42.7% in the 2011 sample. CONCLUSIONS/SIGNIFICANCE We have developed an efficient method that allows DNA methylation to be assessed in archival FFPE tissue samples.
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Affiliation(s)
- Qiling Li
- Department of Obstetrics and Gynecology, First Affiliated Hospital, Xi'an Jiaotong University, Xi'an, Shaanxi, China
- Cardiovascular Research Institute, Morehouse School of Medicine, Atlanta, Georgia, United States of America
| | - Min Li
- School of Information Science and Engineering, Central South University, Changsha, China
| | - Li Ma
- Cardiovascular Research Institute, Morehouse School of Medicine, Atlanta, Georgia, United States of America
| | - Wenzhi Li
- Cardiovascular Research Institute, Morehouse School of Medicine, Atlanta, Georgia, United States of America
| | - Xuehong Wu
- School of Information Science and Engineering, Central South University, Changsha, China
| | - Jendai Richards
- Cardiovascular Research Institute, Morehouse School of Medicine, Atlanta, Georgia, United States of America
| | - Guoxing Fu
- Cardiovascular Research Institute, Morehouse School of Medicine, Atlanta, Georgia, United States of America
| | - Wei Xu
- Cardiovascular Research Institute, Morehouse School of Medicine, Atlanta, Georgia, United States of America
| | - Tameka Bythwood
- Cardiovascular Research Institute, Morehouse School of Medicine, Atlanta, Georgia, United States of America
| | - Xu Li
- Department of Obstetrics and Gynecology, First Affiliated Hospital, Xi'an Jiaotong University, Xi'an, Shaanxi, China
| | - Jianxin Wang
- School of Information Science and Engineering, Central South University, Changsha, China
| | - Qing Song
- Department of Obstetrics and Gynecology, First Affiliated Hospital, Xi'an Jiaotong University, Xi'an, Shaanxi, China
- Cardiovascular Research Institute, Morehouse School of Medicine, Atlanta, Georgia, United States of America
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20
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He W, Li G, Yang CK, Lu CD. Functional characterization of the dguRABC locus for D-Glu and d-Gln utilization in Pseudomonas aeruginosa PAO1. MICROBIOLOGY-SGM 2014; 160:2331-2340. [PMID: 25082951 DOI: 10.1099/mic.0.081141-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
D-Glu, an essential component of peptidoglycans, can be utilized as a carbon and nitrogen source by Pseudomonas aeruginosa. DNA microarrays were employed to identify genes involved in D-Glu catabolism. Through gene knockout and growth phenotype analysis, the divergent dguR-dguABC (D-Glu utilization) gene cluster was shown to participate in D-Glu and D-Gln catabolism and regulation. Growth of the dguR and dguA mutants was abolished completely on D-Glu or retarded on D-Gln as the sole source of carbon and/or nitrogen. The dguA gene encoded a FAD-dependent D-amino acid dehydrogenase with d-Glu as its preferred substrate, and its promoter was specifically induced by exogenous D-Glu and D-Gln. The function of DguR as a transcriptional activator of the dguABC operon was demonstrated by promoter activity measurements in vivo and by mobility shift assays with purified His-tagged DguR in vitro. Although the DNA-binding activity of DguR did not require D-Glu, the presence of D-Glu, but not D-Gln, in the binding reaction was found to stabilize a preferred nucleoprotein complex. The presence of a putative DguR operator was revealed by in silica analysis of the dguR-dguA intergenic regions among Pseudomonas spp. and binding of DguR to a highly conserved 19 bp sequence motif was further demonstrated. The dguB gene encodes a putative enamine/imine deaminase of the RidA family, but its role in D-Glu catabolism remains to be determined. Whilst a lesion in dguC encoding a periplasmic solute binding protein only affected growth on D-Glu slightly, expression of the previously characterized AatJMQP transporter for acidic l-amino acid uptake was found inducible by D-Glu and essential for D-Glu utilization. In summary, the findings of this study supported DguA as a new member of the FAD-dependent d-amino acid dehydrogenase family, and DguR as a D-Glu sensor and transcriptional activator of the dguA promoter.
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Affiliation(s)
- Weiqing He
- Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, PR China.,Department of Biology, Georgia State University, Atlanta, Georgia, USA
| | - Guoqing Li
- Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, PR China.,Department of Biology, Georgia State University, Atlanta, Georgia, USA
| | - Chun-Kai Yang
- Department of Biology, Georgia State University, Atlanta, Georgia, USA
| | - Chung-Dar Lu
- Department of Biology, Georgia State University, Atlanta, Georgia, USA
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Salvi F, Wang YF, Weber IT, Gadda G. Structure of choline oxidase in complex with the reaction product glycine betaine. ACTA ACUST UNITED AC 2014; 70:405-13. [DOI: 10.1107/s1399004713029283] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2013] [Accepted: 10/23/2013] [Indexed: 11/10/2022]
Abstract
Choline oxidase fromArthrobacter globiformis, which is involved in the biosynthesis of glycine betaine from choline, has been extensively characterized in its mechanistic and structural properties. Despite the knowledge gained on the enzyme, the details of substrate access to the active site are not fully understood. The `loop-and-lid' mechanism described for the glucose–methanol–choline enzyme superfamily has not been confirmed for choline oxidase. Instead, a hydrophobic cluster on the solvent-accessible surface of the enzyme has been proposed by molecular dynamics to control substrate access to the active site. Here, the crystal structure of the enzyme was solved in complex with glycine betaine at pH 6.0 at 1.95 Å resolution, allowing a structural description of the ligand–enzyme interactions in the active site. This structure is the first of choline oxidase in complex with a physiologically relevant ligand. The protein structures with and without ligand are virtually identical, with the exception of a loop at the dimer interface, which assumes two distinct conformations. The different conformations of loop 250–255 define different accessibilities of the proposed active-site entrance delimited by the hydrophobic cluster on the other subunit of the dimer, suggesting a role in regulating substrate access to the active site.
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22
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Gadda G. Oxygen Activation in Flavoprotein Oxidases: The Importance of Being Positive. Biochemistry 2012; 51:2662-9. [DOI: 10.1021/bi300227d] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Giovanni Gadda
- Department
of Chemistry, ‡Department of Biology, and §The Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia
30302-4098, United States
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23
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Yuan H, Xin Y, Hamelberg D, Gadda G. Insights on the Mechanism of Amine Oxidation Catalyzed by d-Arginine Dehydrogenase Through pH and Kinetic Isotope Effects. J Am Chem Soc 2011; 133:18957-65. [DOI: 10.1021/ja2082729] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Hongling Yuan
- Department of Chemistry, ‡Department of Biology, and §The Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30302-4098, United States
| | - Yao Xin
- Department of Chemistry, ‡Department of Biology, and §The Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30302-4098, United States
| | - Donald Hamelberg
- Department of Chemistry, ‡Department of Biology, and §The Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30302-4098, United States
| | - Giovanni Gadda
- Department of Chemistry, ‡Department of Biology, and §The Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30302-4098, United States
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24
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Fu G, Yuan H, Wang S, Gadda G, Weber IT. Atomic-Resolution Structure of an N(5) Flavin Adduct in d-Arginine Dehydrogenase. Biochemistry 2011; 50:6292-4. [DOI: 10.1021/bi200831a] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Guoxing Fu
- Department of Biology, ‡Department of Chemistry, and §The Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30303, United States
| | - Hongling Yuan
- Department of Biology, ‡Department of Chemistry, and §The Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30303, United States
| | - Siming Wang
- Department of Biology, ‡Department of Chemistry, and §The Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30303, United States
| | - Giovanni Gadda
- Department of Biology, ‡Department of Chemistry, and §The Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30303, United States
| | - Irene T. Weber
- Department of Biology, ‡Department of Chemistry, and §The Center for Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30303, United States
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Regulation and characterization of the dadRAX locus for D-amino acid catabolism in Pseudomonas aeruginosa PAO1. J Bacteriol 2011; 193:2107-15. [PMID: 21378189 DOI: 10.1128/jb.00036-11] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
D-amino acids are essential components for bacterial peptidoglycan, and these natural compounds are also involved in cell wall remodeling and biofilm disassembling. In Pseudomonas aeruginosa, the dadAX operon, encoding the D-amino acid dehydrogenase DadA and the amino acid racemase DadX, is essential for D- and L-Ala catabolism, and its expression requires a transcriptional regulator, DadR. In this study, purified recombinant DadA alone was sufficient to demonstrate the proposed enzymatic activity with very broad substrate specificity; it utilizes all D-amino acids tested as substrates except D-Glu and D-Gln. DadA also showed comparable k(cat) and K(m) values on D-Ala and several D-amino acids. dadRAX knockout mutants were constructed and subjected to analysis of their growth phenotypes on amino acids. The results revealed that utilization of L-Ala, L-Trp, D-Ala, and a specific set of D-amino acids as sole nitrogen sources was abolished in the dadA mutant and/or severely hampered in the dadR mutant while growth yield on D-amino acids was surprisingly improved in the dadX mutant. The dadA promoter was induced by several L-amino acids, most strongly by Ala, and only by D-Ala among all tested D-amino acids. Enhanced growth of the dadX mutant on D-amino acids is consistent with the finding that the dadA promoter was constitutively induced in the dadX mutant, where exogenous D-Ala but not L-Ala reduced the expression. Binding of DadR to the dadA regulatory region was demonstrated by electromobility shift assays, and the presence of L-Ala but not D-Ala increased affinity by 3-fold. The presence of multiple DadR-DNA complexes in the dadA regulatory region was demonstrated in vitro, and the formation of these nucleoprotein complexes exerted a complicated impact on promoter activation in vivo. In summary, the results from this study clearly demonstrate DadA to be the enzyme solely responsible for the proposed D-amino acid dehydrogenase activity of broad substrate specificity and the physiological functions of DadRAX in catabolism of several D-amino acids and support L-Ala as the signal molecule for induction of the dadAX genes through DadR binding to several putative operator sites.
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