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Human cytochrome P450 11B2 produces aldosterone by a processive mechanism due to the lactol form of the intermediate 18-hydroxycorticosterone.
Reddish MJ, Guengerich FP
(2019) J Biol Chem 294: 12975-12991
MeSH Terms: 18-Hydroxycorticosterone, Aldosterone, Biocatalysis, Cytochrome P-450 CYP11B2, Humans, Kinetics, Models, Molecular, Molecular Conformation
Show Abstract · Added March 3, 2020
Human cytochrome P450 (P450) 11B2 catalyzes the formation of aldosterone, the major endogenous human mineralocorticoid. Aldosterone is important for the regulation of electrolyte homeostasis. Mutations and overexpression of P450 11B2 (also known as aldosterone synthase) can lead to hypertension, congestive heart failure, and diabetic nephropathy. The enzyme is therefore a target for drug development to manage these various disorders. P450 11B2 catalyzes aldosterone formation from 11-deoxycorticosterone through three distinct oxidation steps. It is currently unknown to which degree these reactions happen in sequence without the intermediate products dissociating from the enzyme ( processively) or whether these reactions happen solely distributively, in which the intermediate products must first dissociate and then rebind to the enzyme before subsequent oxidation. We present here a comprehensive investigation of processivity in P450 11B2-catalyzed reactions using steady-state, pre-steady-state, pulse-chase, equilibrium-binding titrations, and stopped-flow binding studies. We utilized the data obtained to develop a kinetic model for P450 11B2 and tested this model by enzyme kinetics simulations. We found that although aldosterone is produced processively, the enzyme preferentially utilizes a distributive mechanism that ends with the production of 18-OH corticosterone. This seemingly contradictory observation could be resolved by considering the ability of the intermediate product 18-OH corticosterone to exist as a lactol form, with the equilibrium favoring the ring-closed lactol configuration. In summary, our refined model for P450 11B2 catalysis indicates isomerization of the intermediate to a lactol can explain why P450 11B2 must produce aldosterone through a processive mechanism despite favoring a distributive mechanism.
© 2019 Reddish and Guengerich.
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8 MeSH Terms
Human cytochrome P450 enzymes bind drugs and other substrates mainly through conformational-selection modes.
Guengerich FP, Wilkey CJ, Phan TTN
(2019) J Biol Chem 294: 10928-10941
MeSH Terms: Catalysis, Cytochrome P-450 CYP2D6, Cytochrome P-450 CYP2E1, Cytochrome P-450 CYP3A, Cytochrome P-450 Enzyme Inhibitors, Cytochrome P-450 Enzyme System, Humans, Kinetics, Lauric Acids, Ligands, Molecular Conformation, Oxidation-Reduction, Palmitic Acid, Protein Binding, Protein Conformation, Spiro Compounds, Substrate Specificity
Show Abstract · Added March 3, 2020
Cytochrome P450 (P450) enzymes are major catalysts involved in the oxidations of most drugs, steroids, carcinogens, fat-soluble vitamins, and natural products. The binding of substrates to some of the 57 human P450s and other mammalian P450s is more complex than a two-state system and has been proposed to involve mechanisms such as multiple ligand occupancy, induced-fit, and conformational-selection. Here, we used kinetic analysis of binding with multiple concentrations of substrates and computational modeling of these data to discern possible binding modes of several human P450s. We observed that P450 2D6 binds its ligand rolapitant in a mechanism involving conformational-selection. P450 4A11 bound the substrate lauric acid via conformational-selection, as did P450 2C8 with palmitic acid. Binding of the steroid progesterone to P450 21A2 was also best described by a conformational-selection model. Hexyl isonicotinate binding to P450 2E1 could be described by either a conformational-selection or an induced-fit model. Simulation of the binding of the ligands midazolam, bromocriptine, testosterone, and ketoconazole to P450 3A4 was consistent with an induced-fit or a conformational-selection model, but the concentration dependence of binding rates for varying both P450 3A4 and midazolam concentrations revealed discordance in the parameters, indicative of conformational-selection. Binding of the P450s 2C8, 2D6, 3A4, 4A11, and 21A2 was best described by conformational-selection, and P450 2E1 appeared to fit either mode. These findings highlight the complexity of human P450-substrate interactions and that conformational-selection is a dominant feature of many of these interactions.
© 2019 Guengerich et al.
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17 MeSH Terms
Isomeric and Conformational Analysis of Small Drug and Drug-Like Molecules by Ion Mobility-Mass Spectrometry (IM-MS).
Phillips ST, Dodds JN, May JC, McLean JA
(2019) Methods Mol Biol 1939: 161-178
MeSH Terms: Algorithms, Amino Acids, Carbohydrates, Ion Mobility Spectrometry, Isomerism, Mass Spectrometry, Molecular Conformation, Pharmaceutical Preparations, Small Molecule Libraries, Software
Show Abstract · Added August 7, 2019
This chapter provides a broad overview of ion mobility-mass spectrometry (IM-MS) and its applications in separation science, with a focus on pharmaceutical applications. A general overview of fundamental ion mobility (IM) theory is provided with descriptions of several contemporary instrument platforms which are available commercially (i.e., drift tube and traveling wave IM). Recent applications of IM-MS toward the evaluation of structural isomers are highlighted and placed in the context of both a separation and characterization perspective. We conclude this chapter with a guided reference protocol for obtaining routine IM-MS spectra on a commercially available uniform-field IM-MS.
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MeSH Terms
Ion mobility conformational lipid atlas for high confidence lipidomics.
Leaptrot KL, May JC, Dodds JN, McLean JA
(2019) Nat Commun 10: 985
MeSH Terms: Animals, Databases, Chemical, Lipids, Mass Spectrometry, Metabolomics, Molecular Conformation, Molecular Structure
Show Abstract · Added August 7, 2019
Lipids are highly structurally diverse molecules involved in a wide variety of biological processes. Here, we use high precision ion mobility-mass spectrometry to compile a structural database of 456 mass-resolved collision cross sections (CCS) of sphingolipid and glycerophospholipid species. Our CCS database comprises sphingomyelin, cerebroside, ceramide, phosphatidylethanolamine, phosphatidylcholine, phosphatidylserine, and phosphatidic acid classes. Primary differences observed are between lipid categories, with sphingolipids exhibiting 2-6% larger CCSs than glycerophospholipids of similar mass, likely a result of the sphingosine backbone's restriction of the sn1 tail length, limiting gas-phase packing efficiency. Acyl tail length and degree of unsaturation are found to be the primary structural descriptors determining CCS magnitude, with degree of unsaturation being four times as influential per mass unit. The empirical CCS values and previously unmapped quantitative structural trends detailed in this work are expected to facilitate prediction of CCS in broadscale lipidomics research.
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Absolute Configurations of Naturally Occurring [5]- and [3]-Ladderanoic Acids: Isolation, Chiroptical Spectroscopy, and Crystallography.
Raghavan V, Johnson JL, Stec DF, Song B, Zajac G, Baranska M, Harris CM, Schley ND, Polavarapu PL, Harris TM
(2018) J Nat Prod 81: 2654-2666
MeSH Terms: Biomass, Bioreactors, Circular Dichroism, Crystallography, X-Ray, Esters, Lipids, Molecular Conformation, Molecular Structure, Spectrum Analysis, Raman, Stereoisomerism
Show Abstract · Added March 3, 2020
We have isolated mixtures of [5]- and [3]-ladderanoic acids 1a and 2a from the biomass of an anammox bioreactor and have separated the acids and their phenacyl esters for the first time by HPLC. The absolute configurations of the naturally occurring acids and their phenacyl esters are assigned as R at the site of side-chain attachment by comparison of experimental specific rotations with corresponding values predicted using quantum chemical (QC) methods. The absolute configurations for 1a and 2a were independently verified by comparison of experimental Raman optical activity spectra with corresponding spectra predicted using QC methods. The configurational assignments of 1a and 2a and of the phenacyl ester of 1a were also confirmed by X-ray crystallography.
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Movement of the RecG Motor Domain upon DNA Binding Is Required for Efficient Fork Reversal.
Warren GM, Stein RA, Mchaourab HS, Eichman BF
(2018) Int J Mol Sci 19:
MeSH Terms: DNA, DNA Helicases, DNA Replication, DNA-Binding Proteins, Models, Molecular, Molecular Conformation, Mutation, Nucleic Acid Conformation, Protein Binding, Protein Interaction Domains and Motifs, Structure-Activity Relationship
Show Abstract · Added August 26, 2019
RecG catalyzes reversal of stalled replication forks in response to replication stress in bacteria. The protein contains a fork recognition ("wedge") domain that binds branched DNA and a superfamily II (SF2) ATPase motor that drives translocation on double-stranded (ds)DNA. The mechanism by which the wedge and motor domains collaborate to catalyze fork reversal in RecG and analogous eukaryotic fork remodelers is unknown. Here, we used electron paramagnetic resonance (EPR) spectroscopy to probe conformational changes between the wedge and ATPase domains in response to fork DNA binding by RecG. Upon binding DNA, the ATPase-C lobe moves away from both the wedge and ATPase-N domains. This conformational change is consistent with a model of RecG fully engaged with a DNA fork substrate constructed from a crystal structure of RecG bound to a DNA junction together with recent cryo-electron microscopy (EM) structures of chromatin remodelers in complex with dsDNA. We show by mutational analysis that a conserved loop within the translocation in RecG (TRG) motif that was unstructured in the RecG crystal structure is essential for fork reversal and DNA-dependent conformational changes. Together, this work helps provide a more coherent model of fork binding and remodeling by RecG and related eukaryotic enzymes.
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Absolute configuration of an axially chiral sulfonate determined from its optical rotatory dispersion, electronic circular dichroism, and vibrational circular dichroism spectra.
Covington CL, Raghavan V, Smuts JP, Armstrong DW, Polavarapu PL
(2017) Chirality 29: 670-676
MeSH Terms: Circular Dichroism, Models, Molecular, Molecular Conformation, Naphthalenes, Optical Rotatory Dispersion, Stereoisomerism, Sulfonic Acids, Vibration
Show Abstract · Added April 10, 2018
The absolute configuration (AC) of an axially chiral sulfonate (aCSO), 3,5-dimethyl-2-(naphthalen-1-yl)-6-(naphthalen-1-yl)benzenesulfonate (labeled as aCSO5), was investigated using optical rotatory dispersion (ORD), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) spectroscopies. All three methods led to the same conclusion and the AC of aCSO5 is reliably determined to be (-)-(aR, aR), or conversely (+)-(aS, aS).
© 2017 Wiley Periodicals, Inc.
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8 MeSH Terms
Investigation of the Complete Suite of the Leucine and Isoleucine Isomers: Toward Prediction of Ion Mobility Separation Capabilities.
Dodds JN, May JC, McLean JA
(2017) Anal Chem 89: 952-959
MeSH Terms: Isoleucine, Isomerism, Leucine, Mass Spectrometry, Molecular Conformation
Show Abstract · Added December 17, 2018
In this study we investigated 11 isomers with the molecular formula CHNO (m/z 131) to ascertain the potential of utilizing drift tube ion mobility mass spectrometry to aid in the separation of isomeric mixtures. This study of small molecules provides a detailed examination of the application of uniform field ion mobility for a narrow scope of isomers with variations in both bond coordination and stereochemistry. For small molecules, it was observed that in general constitutional isomers are more readily separated by uniform field mobility in comparison to stereoisomers such as enantiomers or diastereomers. Diastereomers exhibited differences in their collision cross section (CCS), but were unresolvable in a mixture, whereas the enantiomers studied did not exhibit statistically different CCS values. A mathematical relationship relating the CCS to resolving power was developed in order to predict the required ion mobility resolving power needed to separate the various isomer classes. For the majority of isomers evaluated in this study, a uniform field-based resolving power of 100 was predicted to be sufficient to resolve over half (∼60%) of all hypothetical isomer pairs, including leucine and isoleucine, whereas their stereoisomers (d- and l-forms) are predicted to be significantly more challenging, if not impossible, to separate by conventional drift tube techniques.
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Atropoisomerism in Biflavones: The Absolute Configuration of (-)-Agathisflavone via Chiroptical Spectroscopy.
Covington CL, Junior FM, Silva JH, Kuster RM, de Amorim MB, Polavarapu PL
(2016) J Nat Prod 79: 2530-2537
MeSH Terms: Biflavonoids, Circular Dichroism, Molecular Conformation, Molecular Structure, Optical Rotatory Dispersion, Stereoisomerism
Show Abstract · Added April 10, 2018
The first natural occurrence in optically active form of the dimeric flavonoid agathisflavone and definition of its axial chirality using chiroptical spectroscopic methods are described. The experimental electronic circular dichroism, electronic dissymmetry factor, optical rotatory dispersion, vibrational circular dichroism (VCD), and vibrational dissymmetry factor spectra of agathisflavone are presented and analyzed with their corresponding quantum chemical predictions to definitively assign the axial chirality of (-)-agathisflavone as (aS).
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Six Germline Genetic Variations Impair the Translesion Synthesis Activity of Human DNA Polymerase κ.
Kim JK, Yeom M, Hong JK, Song I, Lee YS, Guengerich FP, Choi JY
(2016) Chem Res Toxicol 29: 1741-1754
MeSH Terms: DNA-Directed DNA Polymerase, Genetic Variation, Humans, Models, Molecular, Molecular Conformation
Show Abstract · Added March 14, 2018
DNA polymerase (pol) κ efficiently catalyzes error-free translesion DNA synthesis (TLS) opposite bulky N-guanyl lesions induced by carcinogens such as polycyclic aromatic hydrocarbons. We investigated the biochemical effects of nine human nonsynonymous germline POLK variations on the TLS properties of pol κ, utilizing recombinant pol κ (residues 1-526) enzymes and DNA templates containing an N-CH(9-anthracenyl)G (N-AnthG), 8-oxo-7,8-dihydroguanine (8-oxoG), O-methyl(Me)G, or an abasic site. In steady-state kinetic analyses, the R246X, R298H, T473A, and R512W variants displayed 7- to 18-fold decreases in k/K for dCTP insertion opposite G and N-AnthG, with 2- to 3-fold decreases in DNA binding affinity, compared to that of the wild-type, and further showed 5- to 190-fold decreases in k/K for next-base extension from C paired with N-AnthG. The A471V variant showed 2- to 4-fold decreases in k/K for correct nucleotide insertion opposite and beyond G (or N-AnthG) compared to that of the wild-type. These five hypoactive variants also showed similar patterns of attenuation of TLS activity opposite 8-oxoG, O-MeG, and abasic lesions. By contrast, the T44M variant exhibited 7- to 11-fold decreases in k/K for dCTP insertion opposite N-AnthG and O-MeG (as well as for dATP insertion opposite an abasic site) but not opposite both G and 8-oxoG, nor beyond N-AnthG, compared to that of the wild-type. These results suggest that the R246X, R298H, T473A, R512W, and A471V variants cause a general catalytic impairment of pol κ opposite G and all four lesions, whereas the T44M variant induces opposite lesion-dependent catalytic impairment, i.e., only opposite O-MeG, abasic, and bulky N-G lesions but not opposite G and 8-oxoG, in pol κ, which might indicate that these hypoactive pol κ variants are genetic factors in modifying individual susceptibility to genotoxic carcinogens in certain subsets of populations.
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5 MeSH Terms