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The unassembled flavoprotein subunits of human and bacterial complex II have impaired catalytic activity and generate only minor amounts of ROS.
Maklashina E, Rajagukguk S, Iverson TM, Cecchini G
(2018) J Biol Chem 293: 7754-7765
MeSH Terms: Bacterial Proteins, Catalysis, Crystallography, X-Ray, Electron Transport Complex II, Escherichia coli, Flavoproteins, Humans, Models, Molecular, Oxidation-Reduction, Protein Conformation, Protein Subunits, Reactive Oxygen Species
Show Abstract · Added April 1, 2019
Complex II (SdhABCD) is a membrane-bound component of mitochondrial and bacterial electron transport chains, as well as of the TCA cycle. In this capacity, it catalyzes the reversible oxidation of succinate. SdhABCD contains the SDHA protein harboring a covalently bound FAD redox center and the iron-sulfur protein SDHB, containing three distinct iron-sulfur centers. When assembly of this complex is compromised, the flavoprotein SDHA may accumulate in the mitochondrial matrix or bacterial cytoplasm. Whether the unassembled SDHA has any catalytic activity, for example in succinate oxidation, fumarate reduction, reactive oxygen species (ROS) generation, or other off-pathway reactions, is not known. Therefore, here we investigated whether unassembled SdhA flavoprotein, its homolog fumarate reductase (FrdA), and the human SDHA protein have succinate oxidase or fumarate reductase activity and can produce ROS. Using recombinant expression in , we found that the free flavoproteins from these divergent biological sources have inherently low catalytic activity and generate little ROS. These results suggest that the iron-sulfur protein SDHB in complex II is necessary for robust catalytic activity. Our findings are consistent with those reported for single-subunit flavoprotein homologs that are not associated with iron-sulfur or heme partner proteins.
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Sulfenylation of Human Liver and Kidney Microsomal Cytochromes P450 and Other Drug-Metabolizing Enzymes as a Response to Redox Alteration.
Albertolle ME, Phan TTN, Pozzi A, Guengerich FP
(2018) Mol Cell Proteomics 17: 889-900
MeSH Terms: Animals, Biocatalysis, Cysteine, Cytochrome P-450 Enzyme System, Humans, Hydrogen Peroxide, Kidney, Mice, Transgenic, Microsomes, Liver, Oxidation-Reduction, Pharmaceutical Preparations, Recombinant Proteins, Staining and Labeling, Sulfenic Acids, Sulfhydryl Compounds
Show Abstract · Added March 14, 2018
The lumen of the endoplasmic reticulum (ER) provides an oxidizing environment to aid in the formation of disulfide bonds, which is tightly regulated by both antioxidant proteins and small molecules. On the cytoplasmic side of the ER, cytochrome P450 (P450) proteins have been identified as a superfamily of enzymes that are important in the formation of endogenous chemicals as well as in the detoxication of xenobiotics. Our previous report described oxidative inhibition of P450 Family 4 enzymes via oxidation of the heme-thiolate cysteine to a sulfenic acid (-SOH) (Albertolle, M. E. (2017) 292, 11230-11242). Further proteomic analyses of murine kidney and liver microsomes led to the finding that a number of other drug-metabolizing enzymes located in the ER are also redox-regulated in this manner. We expanded our analysis of sulfenylated enzymes to human liver and kidney microsomes. Evaluation of the sulfenylation, catalytic activity, and spectral properties of P450s 1A2, 2C8, 2D6, and 3A4 led to the identification of two classes of redox sensitivity in P450 enzymes: heme-thiolate-sensitive and thiol-insensitive. These findings provide evidence for a mammalian P450 regulatory mechanism, which may also be relevant to other drug-metabolizing enzymes. (Data are available via ProteomeXchange with identifier PXD007913.).
© 2018 by The American Society for Biochemistry and Molecular Biology, Inc.
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15 MeSH Terms
Identifying the substrate proteins of U-box E3s E4B and CHIP by orthogonal ubiquitin transfer.
Bhuripanyo K, Wang Y, Liu X, Zhou L, Liu R, Duong D, Zhao B, Bi Y, Zhou H, Chen G, Seyfried NT, Chazin WJ, Kiyokawa H, Yin J
(2018) Sci Adv 4: e1701393
MeSH Terms: Amino Acid Sequence, Bacteriophages, Biocatalysis, Cyclin-Dependent Kinase 4, Endoplasmic Reticulum Stress, HEK293 Cells, Humans, Mutant Proteins, Mutation, Peptides, Proteolysis, Reproducibility of Results, Signal Transduction, Substrate Specificity, Tumor Suppressor Protein p53, Tumor Suppressor Proteins, Ubiquitin, Ubiquitin-Protein Ligase Complexes, Ubiquitin-Protein Ligases, Ubiquitination
Show Abstract · Added March 24, 2018
E3 ubiquitin (UB) ligases E4B and carboxyl terminus of Hsc70-interacting protein (CHIP) use a common U-box motif to transfer UB from E1 and E2 enzymes to their substrate proteins and regulate diverse cellular processes. To profile their ubiquitination targets in the cell, we used phage display to engineer E2-E4B and E2-CHIP pairs that were free of cross-reactivity with the native UB transfer cascades. We then used the engineered E2-E3 pairs to construct "orthogonal UB transfer (OUT)" cascades so that a mutant UB (xUB) could be exclusively used by the engineered E4B or CHIP to label their substrate proteins. Purification of xUB-conjugated proteins followed by proteomics analysis enabled the identification of hundreds of potential substrates of E4B and CHIP in human embryonic kidney 293 cells. Kinase MAPK3 (mitogen-activated protein kinase 3), methyltransferase PRMT1 (protein arginine -methyltransferase 1), and phosphatase PPP3CA (protein phosphatase 3 catalytic subunit alpha) were identified as the shared substrates of the two E3s. Phosphatase PGAM5 (phosphoglycerate mutase 5) and deubiquitinase OTUB1 (ovarian tumor domain containing ubiquitin aldehyde binding protein 1) were confirmed as E4B substrates, and β-catenin and CDK4 (cyclin-dependent kinase 4) were confirmed as CHIP substrates. On the basis of the CHIP-CDK4 circuit identified by OUT, we revealed that CHIP signals CDK4 degradation in response to endoplasmic reticulum stress.
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20 MeSH Terms
Kinetic Deuterium Isotope Effects in Cytochrome P450 Reactions.
Guengerich FP
(2017) Methods Enzymol 596: 217-238
MeSH Terms: Biocatalysis, Cytochrome P-450 Enzyme System, Deuterium, Enzyme Assays, Humans, Hydrogen Bonding, Kinetics, Models, Chemical, Oxidation-Reduction, Substrate Specificity
Show Abstract · Added March 14, 2018
Cytochrome P450 (P450, CYP) research provides many opportunities for the application of kinetic isotope effect (KIE) strategies. P450s collectively catalyze oxidations of more substrates than any other group of enzymes, and CH bond cleavage is a major feature in a large fraction of these reactions. The presence of a significant primary deuterium KIE is evidence that hydrogen abstraction is at least partially rate-limiting in the reactions, and this appears to be the case in many P450 reactions. The first report of a KIE in (P450-linked) drug metabolism appeared in 1961 (for morphine N-demethylation), and in a number of cases, it has been possible to modulate the in vivo metabolism or toxicity of chemicals by deuterium substitution. A number of efforts are in progress to utilize deuterium substitution to alter the metabolism of drugs in an advantageous manner.
© 2017 Elsevier Inc. All rights reserved.
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10 MeSH Terms
Human mitochondrial cytochrome P450 27C1 is localized in skin and preferentially desaturates -retinol to 3,4-dehydroretinol.
Johnson KM, Phan TTN, Albertolle ME, Guengerich FP
(2017) J Biol Chem 292: 13672-13687
MeSH Terms: Biocatalysis, Cytochrome P450 Family 27, Gene Expression Profiling, Gene Expression Regulation, Enzymologic, Humans, Hydrogenation, Hydroxylation, Isoenzymes, Kinetics, Mitochondria, Molecular Structure, Organ Specificity, Oxidation-Reduction, Peptide Fragments, Proteolysis, Proteomics, Skin, Stereoisomerism, Substrate Specificity, Vitamin A
Show Abstract · Added March 14, 2018
Recently, zebrafish and human cytochrome P450 (P450) 27C1 enzymes have been shown to be retinoid 3,4-desaturases. The enzyme is unusual among mammalian P450s in that the predominant oxidation is a desaturation and in that hydroxylation represents only a minor pathway. We show by proteomic analysis that P450 27C1 is localized to human skin, with two proteins of different sizes present, one being a cleavage product of the full-length form. P450 27C1 oxidized all--retinol to 3,4-dehydroretinol, 4-hydroxy (OH) retinol, and 3-OH retinol in a 100:3:2 ratio. Neither 3-OH nor 4-OH retinol was an intermediate in desaturation. No kinetic burst was observed in the steady state; neither the rate of substrate binding nor product release was rate-limiting. Ferric P450 27C1 reduction by adrenodoxin was 3-fold faster in the presence of the substrate and was ∼5-fold faster than the overall turnover. Kinetic isotope effects of 1.5-2.3 (on / ) were observed with 3,3-, 4,4-, and 3,3,4,4-deuterated retinol. Deuteration at C-4 produced a 4-fold increase in 3-hydroxylation due to metabolic switching, with no observable effect on 4-hydroxylation. Deuteration at C-3 produced a strong kinetic isotope effect for 3-hydroxylation but not 4-hydroxylation. Analysis of the products of deuterated retinol showed a lack of scrambling of a putative allylic radical at C-3 and C-4. We conclude that the most likely catalytic mechanism begins with abstraction of a hydrogen atom from C-4 (or possibly C-3) initiating the desaturation pathway, followed by a sequential abstraction of a hydrogen atom or proton-coupled electron transfer. Adrenodoxin reduction and hydrogen abstraction both contribute to rate limitation.
© 2017 by The American Society for Biochemistry and Molecular Biology, Inc.
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Kinetic processivity of the two-step oxidations of progesterone and pregnenolone to androgens by human cytochrome P450 17A1.
Gonzalez E, Guengerich FP
(2017) J Biol Chem 292: 13168-13185
MeSH Terms: 17-alpha-Hydroxypregnenolone, Androstenedione, Animals, Binding Sites, Biocatalysis, Cytochrome P-450 Enzyme Inhibitors, Cytochromes b5, Dehydroepiandrosterone, Humans, Imidazoles, Kinetics, Ligands, Models, Molecular, NADPH-Ferrihemoprotein Reductase, Naphthalenes, Oxidation-Reduction, Pregnenolone, Progesterone, Protein Conformation, Rats, Recombinant Proteins, Stereoisomerism, Steroid 17-alpha-Hydroxylase
Show Abstract · Added March 14, 2018
Cytochrome P450 (P450, CYP) 17A1 plays a critical role in steroid metabolism, catalyzing both the 17α-hydroxylation of pregnenolone and progesterone and the subsequent 17α,20-lyase reactions to form dehydroepiandrosterone (DHEA) and androstenedione (Andro), respectively, critical for generating glucocorticoids and androgens. Human P450 17A1 reaction rates examined are enhanced by the accessory protein cytochrome (), but the exact role of in P450 17A1-catalyzed reactions is unclear as are several details of these reactions. Here, we examined in detail the processivity of the 17α-hydroxylation and lyase steps. did not enhance reaction rates by decreasing the rates of any of the steroids. Steroid binding to P450 17A1 was more complex than a simple two-state system. Pre-steady-state experiments indicated lag phases for Andro production from progesterone and for DHEA from pregnenolone, indicating a distributive character of the enzyme. However, we observed processivity in pregnenolone/DHEA pulse-chase experiments. ()-Orteronel was three times more inhibitory toward the conversion of 17α-hydroxypregnenolone to DHEA than toward the 17α-hydroxylation of pregnenolone. IC values for ()-orteronel were identical for blocking DHEA formation from pregnenolone and for 17α-hydroxylation, suggestive of processivity. Global kinetic modeling helped assign sets of rate constants for individual or groups of reactions, indicating that human P450 17A1 is an inherently distributive enzyme but that some processivity is present, some of the 17α-OH pregnenolone formed from pregnenolone did not dissociate from P450 17A1 before conversion to DHEA. Our results also suggest multiple conformations of P450 17A1, as previously proposed on the basis of NMR spectroscopy and X-ray crystallography.
© 2017 by The American Society for Biochemistry and Molecular Biology, Inc.
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23 MeSH Terms
Oxidation of 1-chloropyrene by human CYP1 family and CYP2A subfamily cytochrome P450 enzymes: catalytic roles of two CYP1B1 and five CYP2A13 allelic variants.
Shimada T, Murayama N, Kakimoto K, Takenaka S, Lim YR, Yeom S, Kim D, Yamazaki H, Guengerich FP, Komori M
(2018) Xenobiotica 48: 565-575
MeSH Terms: Alleles, Aryl Hydrocarbon Hydroxylases, Biocatalysis, Cytochrome P-450 CYP1B1, Humans, Molecular Docking Simulation, Oxidation-Reduction, Pyrenes
Show Abstract · Added March 14, 2018
1. 1-Chloropyrene, one of the major chlorinated polycyclic aromatic hydrocarbon contaminants, was incubated with human cytochrome P450 (P450 or CYP) enzymes including CYP1A1, 1A2, 1B1, 2A6, 2A13, 2B6, 2C9, 2D6, 2E1, 3A4 and 3A5. Catalytic differences in 1-chloropyrene oxidation by polymorphic two CYP1B1 and five CYP2A13 allelic variants were also examined. 2. CYP1A1 oxidized 1-chloropyrene at the 6- and 8-positions more actively than at the 3-position, while both CYP1B1.1 and 1B1.3 preferentially catalyzed 6-hydroxylation. 3. Five CYP2A13 allelic variants oxidized 8-hydroxylation much more than 6- and 3-hydroxylation, and the variant CYP2A13.3 was found to slowly catalyze these reactions with a lower k value than other CYP2A13.1 variants. 4. CYP2A6 catalyzed 1-chloropyrene 6-hydroxylation at a higher rate than the CYP2A13 enzymes, but the rate was lower than the CYP1A1 and 1B1 variants. Other human P450 enzymes had low activities towards 1-chloropyrene. 5. Molecular docking analysis suggested differences in the interaction of 1-chloropyrene with active sites of CYP1 and 2 A enzymes. In addition, a naturally occurring Thr134 insertion in CYP2A13.3 was found to affect the orientation of Asn297 in the I-helix in interacting with 1-chloropyrene (and also 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, NNK) and caused changes in the active site of CYP2A13.3 as compared with CYP2A13.1.
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8 MeSH Terms
cytochrome P450 46A1 (CYP46A1) activation by neuroactive compounds.
Mast N, Anderson KW, Johnson KM, Phan TTN, Guengerich FP, Pikuleva IA
(2017) J Biol Chem 292: 12934-12946
MeSH Terms: Acetylcholine, Allosteric Regulation, Amino Acid Substitution, Anti-HIV Agents, Aspartic Acid, Benzoxazines, Binding Sites, Biocatalysis, Cholesterol 24-Hydroxylase, Deuterium Exchange Measurement, Enzyme Activation, Glutamic Acid, Ligands, Models, Molecular, Molecular Docking Simulation, Mutagenesis, Site-Directed, Mutation, Nerve Tissue Proteins, Peptide Fragments, Protein Conformation, Recombinant Fusion Proteins, gamma-Aminobutyric Acid
Show Abstract · Added March 14, 2018
Cytochrome P450 46A1 (CYP46A1, cholesterol 24-hydroxylase) is the enzyme responsible for the majority of cholesterol elimination from the brain. Previously, we found that the anti-HIV drug efavirenz (EFV) can pharmacologically activate CYP46A1 in mice. Herein, we investigated whether CYP46A1 could also be activated by endogenous compounds, including major neurotransmitters. experiments with purified recombinant CYP46A1 indicated that CYP46A1 is activated by l-glutamate (l-Glu), l-aspartate, γ-aminobutyric acid, and acetylcholine, with l-Glu eliciting the highest increase (3-fold) in CYP46A1-mediated cholesterol 24-hydroxylation. We also found that l-Glu and other activating neurotransmitters bind to the same site on the CYP46A1 surface, which differs from the EFV-binding site. The other principal differences between EFV and l-Glu in CYP46A1 activation include an apparent lack of l-Glu binding to the P450 active site and different pathways of signal transduction from the allosteric site to the active site. EFV and l-Glu similarly increased the CYP46A1 , the rate of the "fast" phase of the enzyme reduction by the redox partner NADPH-cytochrome P450 oxidoreductase, and the amount of P450 reduced. Spectral titrations with cholesterol, in the presence of EFV or l-Glu, suggest that water displacement from the heme iron can be affected in activator-bound CYP46A1. Moreover, EFV and l-Glu synergistically activated CYP46A1. Collectively, our data, along with those from previous cell culture and studies by others, suggest that l-Glu-induced CYP46A1 activation is of physiological relevance.
© 2017 by The American Society for Biochemistry and Molecular Biology, Inc.
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22 MeSH Terms
Pyridine Dinucleotides from Molecules to Man.
Fessel JP, Oldham WM
(2018) Antioxid Redox Signal 28: 180-212
MeSH Terms: ADP-ribosyl Cyclase 1, Adenosine Triphosphate, Biosynthetic Pathways, Catalysis, Disease Susceptibility, Energy Metabolism, Homeostasis, Humans, Hydrolysis, Intracellular Space, Male, Mitochondria, NAD, NADP, NADPH Oxidases, Nitric Oxide Synthase, Oxidation-Reduction, Pyridines, Reactive Oxygen Species, Stress, Physiological
Show Abstract · Added March 14, 2018
SIGNIFICANCE - Pyridine dinucleotides, nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), were discovered more than 100 years ago as necessary cofactors for fermentation in yeast extracts. Since that time, these molecules have been recognized as fundamental players in a variety of cellular processes, including energy metabolism, redox homeostasis, cellular signaling, and gene transcription, among many others. Given their critical role as mediators of cellular responses to metabolic perturbations, it is unsurprising that dysregulation of NAD and NADP metabolism has been associated with the pathobiology of many chronic human diseases. Recent Advances: A biochemistry renaissance in biomedical research, with its increasing focus on the metabolic pathobiology of human disease, has reignited interest in pyridine dinucleotides, which has led to new insights into the cell biology of NAD(P) metabolism, including its cellular pharmacokinetics, biosynthesis, subcellular localization, and regulation. This review highlights these advances to illustrate the importance of NAD(P) metabolism in the molecular pathogenesis of disease.
CRITICAL ISSUES - Perturbations of NAD(H) and NADP(H) are a prominent feature of human disease; however, fundamental questions regarding the regulation of the absolute levels of these cofactors and the key determinants of their redox ratios remain. Moreover, an integrated topological model of NAD(P) biology that combines the metabolic and other roles remains elusive.
FUTURE DIRECTIONS - As the complex regulatory network of NAD(P) metabolism becomes illuminated, sophisticated new approaches to manipulating these pathways in specific organs, cells, or organelles will be developed to target the underlying pathogenic mechanisms of disease, opening doors for the next generation of redox-based, metabolism-targeted therapies. Antioxid. Redox Signal. 28, 180-212.
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Structural and biochemical analyses reveal insights into covalent flavinylation of the Complex II homolog quinol:fumarate reductase.
Starbird CA, Maklashina E, Sharma P, Qualls-Histed S, Cecchini G, Iverson TM
(2017) J Biol Chem 292: 12921-12933
MeSH Terms: Amino Acid Substitution, Biocatalysis, Crystallography, X-Ray, Enzyme Stability, Escherichia coli, Escherichia coli Proteins, Flavin-Adenine Dinucleotide, Gene Deletion, Glutamic Acid, Hot Temperature, Models, Molecular, Molecular Docking Simulation, Mutagenesis, Site-Directed, Mutation, Oxidoreductases, Protein Conformation, Protein Denaturation, Protein Interaction Domains and Motifs, Protein Multimerization, Protein Processing, Post-Translational, Protein Subunits, Recombinant Proteins, Structural Homology, Protein, Succinate Dehydrogenase
Show Abstract · Added April 1, 2019
The Complex II homolog quinol:fumarate reductase (QFR, FrdABCD) catalyzes the interconversion of fumarate and succinate at a covalently attached FAD within the FrdA subunit. The SdhE assembly factor enhances covalent flavinylation of Complex II homologs, but the mechanisms underlying the covalent attachment of FAD remain to be fully elucidated. Here, we explored the mechanisms of covalent flavinylation of the QFR FrdA subunit. Using a Δ strain, we show that the requirement for the assembly factor depends on the cellular redox environment. We next identified residues important for the covalent attachment and selected the FrdA residue, which contributes to proton shuttling during fumarate reduction, for detailed biophysical and structural characterization. We found that QFR complexes containing FrdA have a structure similar to that of the WT flavoprotein, but lack detectable substrate binding and turnover. In the context of the isolated FrdA subunit, the anticipated assembly intermediate during covalent flavinylation, FrdA variants had stability similar to that of WT FrdA, contained noncovalent FAD, and displayed a reduced capacity to interact with SdhE. However, small-angle X-ray scattering (SAXS) analysis of WT FrdA cross-linked to SdhE suggested that the FrdA residue is unlikely to contribute directly to the FrdA-SdhE protein-protein interface. We also found that no auxiliary factor is absolutely required for flavinylation, indicating that the covalent flavinylation is autocatalytic. We propose that multiple factors, including the SdhE assembly factor and bound dicarboxylates, stimulate covalent flavinylation by preorganizing the active site to stabilize the quinone-methide intermediate.
© 2017 by The American Society for Biochemistry and Molecular Biology, Inc.
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