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Antaloae AV, Montigny C, le Maire M, Watson KA, Sørensen TLM. Optimisation of recombinant production of active human cardiac SERCA2a ATPase. PLoS One 2013; 8:e71842. [PMID: 23951256 PMCID: PMC3741278 DOI: 10.1371/journal.pone.0071842] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Accepted: 07/03/2013] [Indexed: 12/16/2022] Open
Abstract
Methods for recombinant production of eukaryotic membrane proteins, yielding sufficient quantity and quality of protein for structural biology, remain a challenge. We describe here, expression and purification optimisation of the human SERCA2a cardiac isoform of Ca(2+) translocating ATPase, using Saccharomyces cerevisiae as the heterologous expression system of choice. Two different expression vectors were utilised, allowing expression of C-terminal fusion proteins with a biotinylation domain or a GFP- His8 tag. Solubilised membrane fractions containing the protein of interest were purified onto Streptavidin-Sepharose, Ni-NTA or Talon resin, depending on the fusion tag present. Biotinylated protein was detected using specific antibody directed against SERCA2 and, advantageously, GFP-His8 fusion protein was easily traced during the purification steps using in-gel fluorescence. Importantly, talon resin affinity purification proved more specific than Ni-NTA resin for the GFP-His8 tagged protein, providing better separation of oligomers present, during size exclusion chromatography. The optimised method for expression and purification of human cardiac SERCA2a reported herein, yields purified protein (> 90%) that displays a calcium-dependent thapsigargin-sensitive activity and is suitable for further biophysical, structural and physiological studies. This work provides support for the use of Saccharomyces cerevisiae as a suitable expression system for recombinant production of multi-domain eukaryotic membrane proteins.
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Affiliation(s)
- Ana V. Antaloae
- School of Biological Sciences, Whiteknights Campus, University of Reading, Reading, Berkshire, United Kingdom
| | - Cédric Montigny
- CEA, iBiTec-S, CNRS, UMR 8221, Universite Paris-Sud, Saclay, France
| | - Marc le Maire
- CEA, iBiTec-S, CNRS, UMR 8221, Universite Paris-Sud, Saclay, France
| | - Kimberly A. Watson
- School of Biological Sciences, Whiteknights Campus, University of Reading, Reading, Berkshire, United Kingdom
- * E-mail: (KAW); (TL-MS)
| | - Thomas L.-M. Sørensen
- Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire, United Kingdom
- * E-mail: (KAW); (TL-MS)
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Wubben TJ, Mesecar AD. Kinetic, thermodynamic, and structural insight into the mechanism of phosphopantetheine adenylyltransferase from Mycobacterium tuberculosis. J Mol Biol 2010; 404:202-19. [PMID: 20851704 DOI: 10.1016/j.jmb.2010.09.002] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2010] [Revised: 08/23/2010] [Accepted: 09/01/2010] [Indexed: 11/30/2022]
Abstract
Phosphopantetheine adenylyltransferase (PPAT) catalyzes the penultimate step in the coenzyme A (CoA) biosynthetic pathway, reversibly transferring an adenylyl group from ATP to 4'-phosphopantetheine (PhP) to form dephosphocoenzyme A. This reaction sits at the branch point between the de novo pathway and the salvage pathway, and has been shown to be a rate-limiting step in the biosynthesis of CoA. Importantly, bacterial and mammalian PPATs share little sequence homology, making the enzyme a potential target for antibiotic development. A series of steady-state kinetic, product inhibition, and direct binding studies with Mycobacterium tuberculosis PPAT (MtPPAT) was conducted and suggests that the enzyme utilizes a nonrapid-equilibrium random bi-bi mechanism. The kinetic response of MtPPAT to the binding of ATP was observed to be sigmoidal under fixed PhP concentrations, but substrate inhibition was observed at high PhP concentrations under subsaturating ATP concentrations, suggesting a preferred pathway to ternary complex formation. Negative cooperativity in the kinetic response of MtPPAT to PhP binding was observed under certain conditions and confirmed thermodynamically by isothermal titration calorimetry, suggesting the formation of an asymmetric quaternary structure during sequential ligation of substrates. Asymmetry in binding was also observed in isothermal titration calorimetry experiments with dephosphocoenzyme A and CoA. X-ray structures of MtPPAT in complex with PhP and the nonhydrolyzable ATP analogue adenosine-5'-[(α,β)-methyleno]triphosphate were solved to 1.57 Å and 2.68 Å, respectively. These crystal structures reveal small conformational changes in enzyme structure upon ligand binding, which may play a role in the nonrapid-equilibrium mechanism. We suggest that the proposed kinetic mechanism and asymmetric character in MtPPAT ligand binding may provide a means of reaction and pathway regulation in addition to that of the previously determined CoA feedback.
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Affiliation(s)
- Thomas J Wubben
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, IL 60607, USA
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Oddi S, Fezza F, Pasquariello N, D'Agostino A, Catanzaro G, De Simone C, Rapino C, Finazzi-Agrò A, Maccarrone M. Molecular Identification of Albumin and Hsp70 as Cytosolic Anandamide-Binding Proteins. ACTA ACUST UNITED AC 2009; 16:624-32. [DOI: 10.1016/j.chembiol.2009.05.004] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2009] [Revised: 04/13/2009] [Accepted: 05/07/2009] [Indexed: 01/09/2023]
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Tian Y, Suk DH, Cai F, Crich D, Mesecar AD. Bacillus anthracis o-succinylbenzoyl-CoA synthetase: reaction kinetics and a novel inhibitor mimicking its reaction intermediate. Biochemistry 2009; 47:12434-47. [PMID: 18973344 DOI: 10.1021/bi801311d] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
o-Succinylbenzoyl-CoA (OSB-CoA) synthetase (EC 6.2.1.26) catalyzes the ATP-dependent condensation of o-succinylbenzoate (OSB) and CoA to form OSB-CoA, the fourth step of the menaquinone biosynthetic pathway in Bacillus anthracis. Gene knockout studies have highlighted this enzyme as a potential target for the discovery of new antibiotics. Here we report the first studies on the kinetic mechanism of B. anthracis OSB-CoA synthetase, classifying it as an ordered bi uni uni bi ping-pong mechanism. Through a series of pre-steady-state and steady-state kinetic studies in conjunction with direct binding studies, it is demonstrated that CoA, the last substrate to bind, strongly activates the first half-reaction after the first round of turnover. The activation of the first half-reaction is most likely achieved by CoA stabilizing conformations of the enzyme in the "F" form, which slowly isomerize back to the E form. Thus, the kinetic mechanism of OSB-CoA synthetase may be more accurately described as an ordered bi uni uni bi iso ping-pong mechanism. The substrate specificity of OSB-CoA synthetase was probed using a series of OSB analogues with alterations in the carboxylate groups. OSB-CoA shows a strong preference for OSB over all of the analogues tested as none were active except 4-[2-(trifluoromethyl)phenyl]-4-oxobutyric acid which exhibited a 100-fold decrease in k(cat)/K(m). On the basis of an understanding of OSB-CoA synthetase's kinetic mechanism and substrate specificity, a reaction intermediate analogue of OSB-AMP, 5'-O-{N-[2-(trifluoromethyl)phenyl]-4-oxobutyl}adenosine sulfonamide (TFMP-butyl-AMS), was designed and synthesized. This inhibitor was found to be an uncompetitive inhibitor to CoA and a mixed-type inhibitor to ATP and OSB with low micromolar inhibition constants. Collectively, these results should serve as an important forerunner to more detailed and extensive inhibitor design studies aimed at developing lead compounds against the OSB-CoA synthetase class of enzymes.
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Affiliation(s)
- Yang Tian
- Center for Pharmaceutical Biotechnology, Department of Medicinal Chemistry and Pharmacognosy, University of Illinois, 900 South Ashland Avenue, Chicago, Illinois 60607, USA
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Qian ZM, Qin SJ, Yi L, Li HJ, Li P, Wen XD. Binding study of Flos Lonicerae Japonicae with bovine serum albumin using centrifugal ultrafiltration and liquid chromatography. Biomed Chromatogr 2008; 22:202-6. [DOI: 10.1002/bmc.916] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Holt A, Smith DJ, Cendron L, Zanotti G, Rigo A, Di Paolo ML. Multiple binding sites for substrates and modulators of semicarbazide-sensitive amine oxidases: kinetic consequences. Mol Pharmacol 2007; 73:525-38. [PMID: 17989349 DOI: 10.1124/mol.107.040964] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Human semicarbazide-sensitive amine oxidase (SSAO) is a target for novel anti-inflammatory drugs that inhibit enzymatic activity. However, progress in developing such drugs has been hampered by an incomplete understanding of mechanisms involved in substrate turnover. We report here results of a comparative study of human and bovine SSAO enzymes that reveal binding of substrates and other ligands to at least two (human) and up to four (bovine) distinct sites on enzyme monomers. Anaerobic spectroscopy reveals binding of substrates (spermidine and benzylamine) and of an imidazoline site ligand (clonidine) to the reduced active site of bovine SSAO, whereas interactions with oxidized enzyme are evident in kinetic assays and crystallization studies. Radioligand binding experiments with [(3)H]tetraphenylphosphonium, an inhibitor of bovine SSAO that binds to an anionic cavity outside the active site, reveal competition with spermidine, benzylamine, and clonidine, indicating that these ligands also bind to this second anionic region. Kinetic models of bovine SSAO are consistent with one spermidine molecule straddling the active and secondary sites on both oxidized and reduced enzyme, whereas these sites are occupied by two individual molecules of smaller substrates such as benzylamine. Clonidine and other imidazoline site ligands enhance or inhibit activity as a result of differing affinities for both sites on oxidized and reduced enzyme. In contrast, although analyses of kinetic data obtained with human SSAO are also consistent with ligands binding to oxidized and reduced enzyme, we observed no apparent requirement for substrate or modulator binding to any secondary site to model enzyme behavior.
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Affiliation(s)
- Andrew Holt
- Department of Pharmacology, Faculty of Medicine and Dentistry, 9-70 Medical Sciences Bldg., University of Alberta, Edmonton, AB, Canada.
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Henrotte V, Vander Elst L, Laurent S, Muller RN. Comprehensive investigation of the non-covalent binding of MRI contrast agents with human serum albumin. J Biol Inorg Chem 2007; 12:929-37. [PMID: 17558523 DOI: 10.1007/s00775-007-0247-5] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2007] [Accepted: 05/02/2007] [Indexed: 11/29/2022]
Abstract
Three techniques, electrospray mass spectrometry, ultrafiltration, and proton relaxometry, are compared in the context of the quantitative analysis of non-covalent binding between human serum albumin (HSA) and MRI contrast agents. The study of the affinity by proton relaxometry reveals the association constant and the number of interaction sites assuming that all sites are identical and independent. Ultrafiltration was adapted for the study of paramagnetic complexes. This technique confirmed the results obtained by relaxometry. Electrospray mass spectrometry, an original method able to study non-covalent binding because of its soft ionization process that allows for the survival of weak binding, provides qualitative and quantitative results. Electrospray mass spectrometry confirmed the affinity measured by proton relaxometry and ultrafiltration. This technique requires very small amounts of products and directly gives the stoichiometry of the association, information not easily obtained by classic techniques. Nevertheless, proton relaxometry remains a useful and mandatory technique for determining the enhancement of the relaxation subsequent to the binding although it demands large amounts of compounds. It is to be pointed out that even if the three techniques lead to a similar ranking of the affinity of the contrast agents for HSA, the absolute values of the association constants disagree as a result of the difference in the experimental conditions (presence of salt, native protein or desalted one, approximations in the fitting of the data, liquid or gas phases).
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Affiliation(s)
- Virginie Henrotte
- Department of General, Organic and Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons-Hainaut, Avenue du Champ de Mars, 24 B-7000 Mons, Belgium
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Abstract
In vitro studies suggest a free bilirubin (B(F)) concentration in the range of 71-770 nmol/L can induce neurotoxicity. In vivo data regarding central nervous system (CNS) B(F) levels have not been determined. We calculated in vivo CNS B(F) levels in Gunn rat pups (15-19 d old; heterozygous nonjaundiced Gunn rats (J/j) and homozygous jaundiced Gunn rats (j/j); saline or sulfadimethoxine treated) based on 1) total brain bilirubin (TBB) content, 2) brain albumin level, 3) CNS bilirubin binding capacity attributable to brain albumin determined using an ultrafiltration technique, and 4) published Gunn rat albumin-bilirubin binding constants (k). Gunn rat brain bilirubin binding capacity was approximately 22 x 10(-3) micromol/g, of which two thirds was accounted for by brain albumin. Using a Gunn rat pup in vivo, k of 9.2 L/micromol, calculated CNS B(F) levels ranged from 72 to 112 nmol/L [95% confidence interval (CI)] in saline and from 59 to 156 nmol/L (95% CI) in sulfadimethoxine-treated J/j pups. These animals demonstrated no neurobehavioral abnormalities and normal cerebellar weight. Calculated CNS B(F) levels were severalfold higher (p < 0.001) in saline (95% CI: 556-1110 nmol/L) and sulfadimethoxine-treated (95% CI: 3461-8985 nmol/L) j/j pups; the former evidenced reduced cerebellar weight; the latter both reduced cerebellar weight and acute neurobehavioral abnormalities. We conclude that calculated CNS B(F) values in j/j pups are substantially higher than those in J/j animals. Given the absence of CNS abnormalities in J/j pups, the presence of such in j/j animals, and the CNS B(F) levels in these groups, we speculate that the CNS B(F) neurotoxicity threshold in vivo is subsumed within the range (71-770 nmol/L) reported in vitro.
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Affiliation(s)
- Monica J Daood
- Department of Pediatrics, Division of Newborn Medicine, University of Pittsburgh School of Medicine, Magee-Womens Research Institute, Pittsburgh, Pennsylvania 15213, USA
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Su X, Kong L, Li X, Chen X, Guo M, Zou H. Biological Fingerprinting Analysis by Liquid Chromatography/Mass Spectrometry for Evaluation of DNA Structural Selectivity of Multiple Compounds in Natural Products. ACTA ACUST UNITED AC 2006; 8:544-50. [PMID: 16827567 DOI: 10.1021/cc060039l] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A method by combination of centrifugal ultrafiltration (CUF) sampling with liquid chromatography-mass spectrometry (LC-MS) analysis was established to evaluate the DNA structure and sequence selectivity of the multiple compounds in a small molecule library. The developed method was applied to analyze the extracts of natural products Coptis chinensis Franch and Rheum palmatum (L.). From the obtained biological fingerprinting chromatograms, 7 compounds in C. chinensis Franch and 11 in R. palmatum (L.) were screened out as DNA binding agents. Most of these compounds were identified by standards and LC-MS analysis after the sample pretreatment with the DNA immobilized cartridge. DNA structural binding preference of the multiple active compounds in these two extracts was then evaluated simultaneously without purification.
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Affiliation(s)
- Xingye Su
- National Chromatographic R. & A. Centre, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
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Fitzpatrick B, O'Kennedy R. The development and application of a surface plasmon resonance-based inhibition immunoassay for the determination of warfarin in plasma ultrafiltrate. J Immunol Methods 2004; 291:11-25. [PMID: 15345301 DOI: 10.1016/j.jim.2004.03.015] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2004] [Revised: 02/26/2004] [Accepted: 03/08/2004] [Indexed: 10/26/2022]
Abstract
Warfarin is the most widely prescribed oral anticoagulant for the management of a wide variety of thromboembolic disorders such as atrial fibrillation and deep vein thrombosis. A panel of warfarin-protein conjugates were produced and characterised and subsequently used for the production of monoclonal antibodies to warfarin. Following characterisation, the monoclonal antibodies were used in the development of a surface plasmon resonance-based inhibition immunoassay for the determination of the physiologically active 'nonprotein'-bound fraction of the drug in plasma ultrafiltrate. The inhibition immunoassay was compared with an existing high-performance liquid chromatography (HPLC) chromatographic technique for the determination of warfarin in plasma ultrafiltrate, and an excellent correlation was achieved between the two independent analytical techniques. The ligand-binding capacity and stability of various immobilised ligands were also compared. The BIACore-based inhibition immunoassay demonstrated an assay precision range of approximately 4-250 ng/ml, which is within the clinical range and demonstrated good reproducibility and robustness.
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Affiliation(s)
- Brian Fitzpatrick
- School of Biotechnology and National Centre for Sensor Research, Dublin City University, Glasnevin, Dublin 9, Ireland
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Lenoir G, Picard M, Møller JV, le Maire M, Champeil P, Falson P. Involvement of the L6-7 loop in SERCA1a Ca2+-ATPase activation by Ca2+ (or Sr2+) and ATP. J Biol Chem 2004; 279:32125-33. [PMID: 15155750 DOI: 10.1074/jbc.m402934200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Wild-type (WT) and the double mutant D813A,D818A (ADA) of the L6-7 loop of SERCA1a were expressed in yeast, purified, and reconstituted into lipids. This allowed us to functionally study these ATPases by both kinetic and spectroscopic means, and to solve previous discrepancies in the published literature about both experimental facts and interpretation concerning the role of this loop in P-type ATPases. We show that in a solubilized state, the ADA mutant experiences a dramatic decrease of its calcium-dependent ATPase activity. On the contrary, reconstituted in a lipid environment, it displays an almost unaltered maximal calcium-dependent ATPase activity at high (millimolar) ATP, with an apparent affinity for Ca(2+) altered only moderately (3-fold). In the absence of ATP, the true affinity of ADA for Ca(2+) is, however, more significantly reduced (20-30-fold) compared with WT, as judged from intrinsic (Trp) or extrinsic (fluorescence isothiocyanate) fluorescence experiments. At low ATP, transient kinetics experiments reveal an overshoot in the ADA phosphorylation level primarily arising from the slowing down of the transition between the nonphosphorylated "E2" and "Ca(2)E1" forms of ADA. At high ATP, this slowing down is only partially compensated for, as ADA turnover remains more sensitive to orthovanadate than WT turnover. ADA ATPase also proved to have a reduced affinity for ATP in studies performed under equilibrium conditions in the absence of Ca(2+), highlighting the long range interactions between L6-7 and the nucleotide-binding site. We propose that these mutations in L6-7 could affect protonation-dependent winding and unwinding events in the nearby M6 transmembrane segment.
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Affiliation(s)
- Guillaume Lenoir
- Unité de Recherche Associée 2096, the Centre National de la Recherche Scientifique and Section de Biophysique des Fonctions Membranaires, Département de Biologie Joliot Curie, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
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12
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Wang LH, Weng LX, Dong YH, Zhang LH. Specificity and Enzyme Kinetics of the Quorum-quenching N-Acyl Homoserine Lactone Lactonase (AHL-lactonase). J Biol Chem 2004; 279:13645-51. [PMID: 14734559 DOI: 10.1074/jbc.m311194200] [Citation(s) in RCA: 167] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
N-Acyl homoserine lactone (AHL) quorum-sensing signals are the vital elements of bacterial quorum-sensing systems, which regulate diverse biological functions, including virulence. The AHL-lactonase, a quorumquenching enzyme encoded by aiiA from Bacillus sp., inactivates AHLs by hydrolyzing the lactone bond to produce corresponding N-acyl homoserines. To characterize the enzyme, the recombinant AHL-lactonase and its four variants were purified. Kinetic and substrate specificity analysis showed that AHL-lactonase had no or little residue activity to non-acyl lactones and noncyclic esters, but displayed strong enzyme activity toward all tested AHLs, varying in length and nature of the substitution at the C3 position of the acyl chain. The data also indicate that the amide group and the ketone at the C1 position of the acyl chain of AHLs could be important structural features in enzyme-substrate interaction. Surprisingly, although carrying a (104)HX- HXDH(109) short sequence identical to the zinc-binding motif of several groups of metallohydrolytic enzymes, AHL-lactonase does not contain or require zinc or other metal ions for enzyme activity. Except for the amino acid residue His-104, which was shown previously to not be required for catalysis, kinetic study and conformational analysis using circular dichroism spectrometry showed that substitution of the other key residues in the motif (His-106, Asp-108, and His-109), as well as His-169 with serine, respectively, caused conformational changes and significant loss of enzyme activity. We conclude that AHL-lactonase is a highly specific enzyme and that the (106)HXDH(109) approximately H(169) of AHL-lactonase represents a novel catalytic motif, which does not rely on zinc or other metal ions for activity.
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Affiliation(s)
- Lian-Hui Wang
- Institute of Molecular and Cell Biology, 30 Medical Drive, Singapore 117609.
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Ouellet M, Falgueyret JP, Percival MD. Detergents profoundly affect inhibitor potencies against both cyclo-oxygenase isoforms. Biochem J 2004; 377:675-84. [PMID: 14510637 PMCID: PMC1223887 DOI: 10.1042/bj20030969] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2003] [Revised: 09/19/2003] [Accepted: 09/26/2003] [Indexed: 11/17/2022]
Abstract
The sensitivity of Coxs (cyclo-oxygenases) to inhibition is known to be highly dependent on assay conditions. In the present study, the inhibitor sensitivities of purified Cox-1 and -2 were determined in a colorimetric assay using the reducing agent N, N, N ', N '-tetramethyl- p -phenylenediamine. With the detergent genapol X-100 (2 mM) present, the potencies of nimesulide, ibuprofen, flufenamic acid, niflumic acid and naproxen were increased over 100-fold against Cox-2 and titration curve shapes changed, so that maximal inhibition now approached 100%. Indomethacin, diclofenac and flosulide were not changed in potency. Similar effects of genapol were observed with inhibitors of Cox-1. DuP-697 and two analogues became more than 10-fold less potent against Cox-2 with genapol present. Tween-20, Triton X-100 and phosphatidylcholine, but not octylglucoside, gave qualitatively similar effects as genapol. Similar detergent-dependent changes in inhibitor potency were also observed using a [(14)C]arachidonic acid HPLC assay. The increases in potency of ibuprofen, flufenamic acid, isoxicam and niflumic acid towards Cox-2 and ibuprofen towards Cox-1 were accompanied by a change from time-independent to time-dependent inhibition. The interactions of Cox inhibitors has been described in terms of multiple binding step mechanisms. The genapol-dependent increase in inhibitor potency for ketoprofen was associated with an increase in the rate constant for the conversion of the initial enzyme-inhibitor complex to a second, more tightly bound form. The loss of potency for some inhibitors is probably due to inhibitor partitioning into detergent micelles. The present study identifies detergents as another factor that must be considered when determining inhibitor potencies against both Cox isoforms.
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Affiliation(s)
- Marc Ouellet
- Department of Biochemistry and Molecular Biology, Merck Frosst Centre for Therapeutic Research, Pointe-Claire-Dorval, Quebec, Canada
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14
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Samimi A, Last JA. Mechanism of inhibition of lysyl hydroxylase activity by the organophosphates malathion and malaoxon. Toxicol Appl Pharmacol 2001; 176:181-6. [PMID: 11714250 DOI: 10.1006/taap.2001.9275] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Direct inhibition of lysyl hydroxylase by malathion and malaoxon was observed in an in vitro enzyme assay with recombinant lysyl hydroxylase expressed via a baculoviral system. The IC50 values for malathion and malaoxon were estimated to be approximately 60 and 45 mM, respectively. Additional kinetic studies showed this inhibition to be competitive or partially competitive with respect to the synthetic (collagen) peptide, partially uncompetitive with respect to Fe(2+), and partially noncompetitive with respect to ascorbic acid. The calculated values for the K(i) were consistent with the IC50 values. Allosteric effects were not found for any of the cofactors tested, the peptide substrate, or the inhibitors. Interactions were found to be unimolecular for lysyl hydroxylase and its substrate and cofactors as well as for the inhibitors malathion and malaoxon. A computer search of a protein structure database showed an unexpected region of partial homology between the active site sequence of acetylcholinesterase and a segment of lysyl hydroxylase, suggesting a possible molecular basis for these observations. These results suggest the possibility of a novel and hitherto unexpected class of inhibitors of lysyl hydroxylase, based on the organophosphate structure, that might be of value for testing as antifibrotic drugs.
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Affiliation(s)
- A Samimi
- Pulmonary/Critical Care Medicine, University of California, Davis, California 95616, USA
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15
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Champeil P, Menguy T, Tribet C, Popot JL, le Maire M. Interaction of amphipols with sarcoplasmic reticulum Ca2+-ATPase. J Biol Chem 2000; 275:18623-37. [PMID: 10747917 DOI: 10.1074/jbc.m000470200] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Amphipols are short-chain amphipathic polymers designed to keep membrane proteins soluble in aqueous solutions. We have evaluated the effects of the interaction of amphipols with sarcoplasmic reticulum Ca(2+)-ATPase either in a membrane-bound or a soluble form. If the addition of amphipols to detergent-solubilized ATPase was followed by removal of detergent, soluble complexes formed, but these complexes retained poor ATPase activity, were not very stable upon long incubation periods, and at high concentrations they experienced aggregation. Nevertheless, adding excess detergent to diluted detergent-free ATPase-amphipol complexes incubated for short periods immediately restored full activity to these complexes, showing that amphipols had protected solubilized ATPase from the rapid and irreversible inactivation that otherwise follows detergent removal. Amphipols also protected solubilized ATPase from the rapid and irreversible inactivation observed in detergent solutions if the ATPase Ca(2+) binding sites remain vacant. Moreover, in the presence of Ca(2+), amphipol/detergent mixtures stabilized concentrated ATPase against inactivation and aggregation, whether in the presence or absence of lipids, for much longer periods of time (days) than detergent alone. Our observations suggest that mixtures of amphipols and detergents are promising media for handling solubilized Ca(2+)-ATPase under conditions that would otherwise lead to its irreversible denaturation and/or aggregation.
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Affiliation(s)
- P Champeil
- Unité de Recherche Associée 2096 (CNRS et CEA) and Section de Biophysique des Protéines et des Membranes, Département de Biologie Cellulaire et Moléculaire, Commissariat à l'Energie Atomique Saclay, 91191 Gif-sur-Yvette Cedex, France
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