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Kobayashi Y, Nanba Y, Tanabe S. A New Method of Deuterium Incorporation to TMS-Epoxyalcohol Using Sodium Methylsulfinylmethylide-d5 (NaDMSO-d5). HETEROCYCLES 2018. [DOI: 10.3987/com-18-s(t)32] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Wu G, Tsai AL. Dynamics of Radical Intermediates in Prostaglandin H Synthase-1 Cyclooxygenase Reactions is Modulated by Multiple Factors. Protein Pept Lett 2017; 23:1013-1023. [PMID: 27748183 DOI: 10.2174/0929866523666161007151812] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Revised: 09/30/2016] [Accepted: 10/01/2016] [Indexed: 11/22/2022]
Abstract
Prostaglandin H synthase (PGHS) catalyzes the biosynthesis of PGG2 and PGH2, the precursor of all prostanoids, from arachidonic acid (AA). PGHS exhibits two enzymatic activities following a branched-chain radical mechanism: 1) a peroxidase activity (POX) that utilizes hydroperoxide through heme redox cycles to generate the critical Tyr385 tyrosyl radical for coupling both enzyme activities; 2) the cyclooxygenase (COX) activity inserting two oxygen molecules into AA to generate endoperoxide/hydroperoxide PGG2 through a series of radical intermediates. Upon the generation of Tyr385 radical, COX catalysis is initiated, with C13 pro-S hydrogen abstraction from AA by Tyr385 radical to generate arachidonyl substrate radical. Oxygen provides a large driving force for the subsequent fast steps leading to the formation of PGG2, including radical redistributions, ring formations, and rearrangements. On the other hand, if the supply of oxygen is severed, equilibrium between arachidonyl radical and tyrosyl radical(s) biases largely towards the latter. In this study, we demonstrate that such equilibrium is shifted by many factors, including temperature, chemical structures of fatty acid substrates and limited supply of oxygen. We also, for the first time, reveal that this equilibrium is significantly affected by co-substrates of POX. The presence of efficient POX co-substrates, which reduces heme to its ferric state, apparently biases the equilibrium towards arachidonyl radical. Therefore a dynamic interplay exists between the two activities of PGHS.
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Affiliation(s)
- Gang Wu
- Division of Hematology, Department of Internal Medicine, the University of Texas Health Science Center at Houston - McGovern Medical School, MSB 5.290, 6431 Fannin, Houston, TX 77030, USA
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Audran G, Brémond P, Marque SR, Siri D, Santelli M. Energetics of the biosynthesis of prostanes from arachidonate. Tetrahedron 2015. [DOI: 10.1016/j.tet.2015.07.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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Kinetic Isotope Effect of Prostaglandin H Synthase Exhibits Inverted Temperature Dependence. Catalysts 2014. [DOI: 10.3390/catal4020174] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
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Lü JM, Rogge CE, Wu G, Kulmacz RJ, van der Donk WA, Tsai AL. Cyclooxygenase reaction mechanism of PGHS--evidence for a reversible transition between a pentadienyl radical and a new tyrosyl radical by nitric oxide trapping. J Inorg Biochem 2011; 105:356-65. [PMID: 21403766 DOI: 10.1016/j.jinorgbio.2010.11.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Incubation of prostaglandin H synthase-1 (PGHS-1) under anaerobic conditions with peroxide and arachidonic acid leads to two major radical species: a pentadienyl radical and a radical with a narrow EPR spectrum. The proportions of the two radicals are sensitive to temperature, favoring the narrow radical species at 22 °C. The EPR characteristics of this latter radical are somewhat similar to the previously reported narrow-singlet tyrosine radical NS1a and are insensitive to deuterium labeling of AA. To probe the origin and structure of this radical, we combined EPR analysis with nitric oxide (NO) trapping of tyrosine and substrate derived radicals for both PGHS-1 and -2. Formation of 3-nitrotyrosine in the proteins was analyzed by immunoblotting, whereas NO adducts to AA and AA metabolites were analyzed by mass spectrometry and by chromatography of (14)C-labeled products. The results indicate that both nitrated tyrosine residues and NO-AA adducts formed upon NO trapping. The NO-AA adduct was predominantly an oxime at C11 of AA with three conjugated double bonds, as indicated by absorption at 275 nm and by mass spectral analysis. This adduct amounted to 10% and 20% of the heme concentration of PGHS-1 and -2, respectively. For PGHS-1, the yield of NO-AA adduct matched the yield of the narrow radical signal obtained in parallel EPR experiments. High frequency EPR characterization of this narrow radical, reported in an accompanying paper, supports assignment to a new tyrosyl radical, NS1c, rather than an AA-based radical. To reconcile the results from EPR and NO-trapping studies, we propose that the NS1c is in equilibrium with an AA pentadienyl radical, and that the latter reacts preferentially with NO.
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Affiliation(s)
- Jian-Ming Lü
- Department of Internal Medicine, University of Texas Medical School at Houston, Houston, Texas 77030, USA
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Cyclooxygenase reaction mechanism of prostaglandin H synthase from deuterium kinetic isotope effects. J Inorg Biochem 2011; 105:382-90. [PMID: 21394223 DOI: 10.1016/j.jinorgbio.2010.11.015] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Cyclooxygenase catalysis by prostaglandin H synthase (PGHS) is thought to involve a multistep mechanism with several radical intermediates. The proposed mechanism begins with transfer of the C13 pro-(S) hydrogen atom from the substrate arachidonic acid (AA) to the Tyr385 radical in PGHS, followed by oxygen insertion and several bond rearrangements. The importance of the hydrogen-transfer step to controlling the overall kinetics of cyclooxygenase catalysis has not been directly examined. We quantified the non-competitive primary kinetic isotope effect (KIE) for both PGHS-1 and -2 using unlabeled AA and several deuterated AAs, including 13-pro-(S) d-AA, 13,13-d(2)-AA and 10, 10, 13,13-d(4)-AA. The primary KIE for steady-state cyclooxygenase catalysis, (D)k(cat), ranged between 1.8 and 2.3 in oxygen electrode measurements. The intrinsic KIE of AA radical formation by C13 pro-(S) hydrogen abstraction in PGHS-1 was estimated to be 1.9-2.3 using rapid freeze-quench EPR kinetic analysis of anaerobic reactions and computer modeling to a mechanism that includes slow formation of a pentadienyl AA radical and rapid equilibration of the AA radical with a tyrosyl radical, NS1c. The observation of similar values for steady-state and pre-steady state KIEs suggests that hydrogen abstraction is a rate-limiting step in cyclooxygenase catalysis. The large difference of the observed KIE from that of lipoxygenase indicates very different mechanism of hydrogen transfer.
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Tsai AL, Wu G, Rogge CE, Lü JM, Peng S, van der Donk WA, Palmer G, Gerfen GJ, Kulmacz RJ. Structural comparisons of arachidonic acid-induced radicals formed by prostaglandin H synthase-1 and -2. J Inorg Biochem 2011; 105:366-74. [PMID: 21421123 DOI: 10.1016/j.jinorgbio.2010.11.012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2010] [Revised: 11/15/2010] [Accepted: 11/19/2010] [Indexed: 11/15/2022]
Abstract
Cyclooxygenase catalysis by prostaglandin H synthase (PGHS)-1 and -2 involves reaction of a peroxide-induced Tyr385 radical with arachidonic acid (AA) to form an AA radical that reacts with O(2). The potential for isomeric AA radicals and formation of an alternate tyrosyl radical at Tyr504 complicate analysis of radical intermediates. We compared the EPR spectra of PGHS-1 and -2 reacted with peroxide and AA or specifically deuterated AA in anaerobic, single-turnover experiments. With peroxide-treated PGHS-2, the carbon-centered radical observed after AA addition was consistently a pentadienyl radical; a variable wide-singlet (WS) contribution from mixture of Tyr385 and Tyr504 radicals was also present. Analogous reactions with PGHS-1 produced EPR signals consistent with varying proportions of pentadienyl and tyrosyl radicals, and two additional EPR signals. One, insensitive to oxygen exposure, is the narrow singlet tyrosyl radical with clear hyperfine features found previously in inhibitor-pretreated PGHS-1. The second type of EPR signal is a narrow singlet lacking detailed hyperfine features that disappeared upon oxygen exposure. This signal was previously ascribed to an allyl radical, but high field EPR analysis indicated that ~90% of the signal originates from a novel tyrosyl radical, with a small contribution from a carbon-centered species. The radical kinetics could be resolved by global analysis of EPR spectra of samples trapped at various times during anaerobic reaction of PGHS-1 with a mixture of peroxide and AA. The improved understanding of the dynamics of AA and tyrosyl radicals in PGHS-1 and -2 will be useful for elucidating details of the cyclooxygenase mechanism, particularly the H-transfer between tyrosyl radical and AA.
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Affiliation(s)
- Ah-lim Tsai
- Department of Internal Medicine, University of Texas Health Science Center at Houston, Houston, TX 77030, USA.
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Jacquot C, Peng S, van der Donk WA. Kinetic isotope effects in the oxidation of arachidonic acid by soybean lipoxygenase-1. Bioorg Med Chem Lett 2008; 18:5959-62. [PMID: 18793849 PMCID: PMC2652760 DOI: 10.1016/j.bmcl.2008.08.108] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2008] [Revised: 08/23/2008] [Accepted: 08/26/2008] [Indexed: 11/22/2022]
Abstract
The reaction of soybean lipoxygenase-1 with linoleic acid has been extensively studied and displays very large kinetic isotope effects. In this work, substrate and solvent kinetic isotope effects as well as the viscosity dependence of the oxidation of arachidonic acid were investigated. The hydrogen atom abstraction step was rate-determining at all temperatures, but was partially masked by a viscosity-dependent step at ambient temperatures. The observed KIEs on k(cat) were large ( approximately 100 at 25 degrees C).
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Affiliation(s)
- Cyril Jacquot
- Roger Adams Laboratory, Department of Chemistry, University of Illinois, 600 S. Mathews Avenue, Urbana, IL 61801, USA
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Jacquot C, Wecksler AT, McGinley CM, Segraves EN, Holman TR, van der Donk WA. Isotope sensitive branching and kinetic isotope effects in the reaction of deuterated arachidonic acids with human 12- and 15-lipoxygenases. Biochemistry 2008; 47:7295-303. [PMID: 18547056 DOI: 10.1021/bi800308q] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Lipoxygenases (LOs) catalyze lipid peroxidation and have been implicated in a number of human diseases connected to oxidative stress and inflammation. These enzymes have also attracted considerable attention due to large kinetic isotope effects (30-80) for the rate-limiting hydrogen abstraction step with linoleic acid (LA) as substrate. Herein, we report kinetic isotope effects (KIEs) in the reactions of three human LOs (platelet 12-hLO, reticulocyte 15-hLO-1, and epithelial 15-hLO-2) with arachidonic acid (AA). Surprisingly, the observed KIEs with AA were much smaller than the previously reported values with LA. Investigation into the origins for the smaller KIEs led to the discovery of isotope sensitive branching of the reaction pathways. Product distribution analysis demonstrated an inversion in the regioselectivity of 15-hLO-1, with hydrogen abstraction from C13 being the major pathway with unlabeled AA but abstraction from C10 predominating when the methylene group at position 13 was deuterated. Smaller but clear changes in regioselectivity were also observed for 12-hLO and 15-hLO-2.
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Affiliation(s)
- Cyril Jacquot
- Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA
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McGinley CM, Jacquot C, van der Donk WA. Synthesis of 7-thiaarachidonic acid as a mechanistic probe of prostaglandin H synthase-2. Bioorg Med Chem Lett 2007; 17:4049-52. [PMID: 17485208 PMCID: PMC2040112 DOI: 10.1016/j.bmcl.2007.04.073] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2007] [Revised: 04/20/2007] [Accepted: 04/23/2007] [Indexed: 11/16/2022]
Abstract
The mechanism by which prostaglandin synthase converts arachidonic acid to prostaglandin G(2), creating five new chiral centers in the process, is still incompletely understood. The first radical intermediate has been characterized by EPR spectroscopy but subsequent proposed intermediates have not succumbed to detection. We report the synthesis of 7-thiaarachidonic acid designed to stabilize one of the proposed radical intermediates, which may allow its detection.
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Affiliation(s)
- Chris M McGinley
- Roger Adams Laboratory, Department of Chemistry, University of Illinois, 600 S. Mathews Avenue, Urbana, IL 61801, USA
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Abstract
This Perspective provides an overview of the progress in two of the original programs in my research group focused on the biosynthesis of the antibiotics nisin, lacticin 481, fosfomycin, and bialaphos. The path from start-up funds to tenure and beyond offers insights into the opportunities realized and missed along the road.
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Affiliation(s)
- Wilfred A van der Donk
- Roger Adams Laboratory, Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
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Affiliation(s)
- Perry A Frey
- Department of Biochemistry, University of Wisconsin-Madison, 1710 University Avenue, Madison, Wisconsin 53726, USA
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Furse KE, Pratt DA, Porter NA, Lybrand TP. Molecular dynamics simulations of arachidonic acid complexes with COX-1 and COX-2: insights into equilibrium behavior. Biochemistry 2006; 45:3189-205. [PMID: 16519514 PMCID: PMC2504530 DOI: 10.1021/bi052337p] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The cyclooxygenase (COX) enzymes are responsible for the committed step in prostaglandin biosynthesis, the generation of prostaglandin H(2). As a result, these enzymes are pharmacologically important targets for nonsteroidal antiinflammatory drugs, such as aspirin and newer COX-2 selective inhibitors. The cyclooxygenases are functional homodimers, and each subunit contains both a cyclooxygenase and a peroxidase active site. These enzymes are quite interesting mechanistically, as the conversion of arachidonic acid to prostaglandin H(2) requires two oxygenation and two cyclization reactions, resulting in the formation of five new chiral centers with nearly absolute regio- and stereochemical fidelity. We have used molecular dynamics (MD) simulations to investigate the equilibrium behavior of both COX-1 and COX-2 enzyme isoforms with bound arachidonate. These simulations were compared with reference simulations of arachidonate in solution to explore the effect of enzyme on substrate conformation and positioning in the active site. The simulations suggest that the substrate has greater conformational freedom in the COX-2 active site, consistent with the larger COX-2 active site volume observed in X-ray crystal structures. The simulations reveal different conformational behavior for arachidonate in each subunit over the course of extended equilibrium MD simulations. The simulations also provide detailed information for several protein channels that might be important for oxygen and water transport to or from active sites or for intermediate trafficking between the cyclooxygenase and peroxidase active sites. The detailed comparisons for COX-1 versus COX-2 active site structural fluctuations may also provide useful information for design of new isozyme-selective inhibitors.
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Affiliation(s)
- Kristina E Furse
- Department of Chemistry, Center for Structural Biology, Vanderbilt University, 5142 Biosciences/MRB III, Nashville, Tennessee 37232-8725, USA
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Furse KE, Pratt DA, Schneider C, Brash AR, Porter NA, Lybrand TP. Molecular dynamics simulations of arachidonic acid-derived pentadienyl radical intermediate complexes with COX-1 and COX-2: insights into oxygenation regio- and stereoselectivity. Biochemistry 2006; 45:3206-18. [PMID: 16519515 PMCID: PMC2504531 DOI: 10.1021/bi052338h] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The two cyclooxygenase enzymes, COX-1 and COX-2, are responsible for the committed step in prostaglandin biosynthesis and are the targets of the nonsteroidal antiinflammatory drugs aspirin and ibuprofen and the COX-2 selective inhibitors, Celebrex, Vioxx, and Bextra. The enzymes are remarkable in that they catalyze two dioxygenations and two cyclizations of the native substrate, arachidonic acid, with near absolute regio- and stereoselectivity. Several theories have been advanced to explain the nature of enzymatic control over this series of reactions, including suggestions of steric shielding and oxygen channeling. As proposed here, selective radical trapping and spin localization in the substrate-derived pentadienyl radical intermediate can also be envisioned. Herein we describe the results of explicit, 10 ns molecular dynamics simulations of both COX-1 and COX-2 with the substrate-derived pentadienyl radical intermediate bound in the active site. The enzymes' influence on the conformation of the pentadienyl radical was investigated, along with the accessible space above and below the radical plane and the width of several channels to the active site that could function as access routes for molecular oxygen. Additional simulations demonstrated the extent of molecular oxygen mobility within the active site. The results suggest that spin localization is unlikely to play a role in enzymatic control of this reaction. Instead, a combination of oxygen channeling, steric shielding, and selective radical trapping appears to be responsible. This work adds a dynamic perspective to the strong foundation of static structural data available for these enzymes.
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Affiliation(s)
- Kristina E Furse
- Department of Chemistry, Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37232, USA
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McGinley CM, van der Donk WA. Synthesis of site-specifically deuterated arachidonic acid derivatives containing a remote tritium radiolabel. J Labelled Comp Radiopharm 2006; 49:545-558. [DOI: 10.1002/jlcr.1073] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Kulmacz RJ, van der Donk WA, Tsai AL. Comparison of the properties of prostaglandin H synthase-1 and -2. Prog Lipid Res 2003; 42:377-404. [PMID: 12814642 DOI: 10.1016/s0163-7827(03)00023-7] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Biosynthesis of prostanoid lipid signaling agents from arachidonic acid begins with prostaglandin H synthase (PGHS), a hemoprotein in the myeloperoxidase family. Vertebrates from humans to fish have two principal isoforms of PGHS, termed PGHS-1 and-2. These two isoforms are structurally quite similar, but they have very different pathophysiological roles and are regulated very differently at the level of catalysis. The focus of this review is on the structural and biochemical distinctions between PGHS-1 and-2, and how these differences relate to the functional divergence between the two isoforms.
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Affiliation(s)
- Richard J Kulmacz
- Department of Internal Medicine, University of Texas Health Science Center at Houston, Houston, TX 77030, USA.
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Rouzer CA, Marnett LJ. Mechanism of free radical oxygenation of polyunsaturated fatty acids by cyclooxygenases. Chem Rev 2003; 103:2239-304. [PMID: 12797830 DOI: 10.1021/cr000068x] [Citation(s) in RCA: 184] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Carol A Rouzer
- A. B. Hancock Jr. Memorial Laboratory for Cancer Research, Department of Biochemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt Ingram Comprehensive Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, USA
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Tsai AL, Palmer G, Wu G, Peng S, Okeley NM, van der Donk WA, Kulmacz RJ. Structural characterization of arachidonyl radicals formed by aspirin-treated prostaglandin H synthase-2. J Biol Chem 2002; 277:38311-21. [PMID: 12167656 DOI: 10.1074/jbc.m206961200] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Peroxide-generated tyrosyl radicals in both prostaglandin H synthase (PGHS) isozymes have been demonstrated to couple the peroxidase and cyclooxygenase activities by serving as the immediate oxidant for arachidonic acid (AA) in cyclooxygenase catalysis. Acetylation of Ser-530 of PGHS-1 by aspirin abolishes all oxygenase activity and transforms the peroxide-induced tyrosyl radical from a functional 33-35-gauss (G) wide doublet/wide singlet to a 26-G narrow singlet unable to oxidize AA. In contrast, aspirin-treated PGHS-2 (ASA-PGHS-2) no longer forms prostaglandins but retains oxygenase activity forming 11(R)- and 15(R)-hydroperoxyeicosatetraenoic acid and also retains the EPR line-shape of the native peroxide-induced 29-30-G wide singlet radical. To evaluate the functional role of the wide singlet radical in ASA-PGHS-2, we have examined the ability of this radical to oxidize AA in single-turnover EPR studies. Anaerobic addition of AA to ASA-PGHS-2 immediately after formation of the wide singlet radical generated either a 7-line EPR signal similar to the pentadienyl AA radical obtained in native PGHS-2 or a 26-28-G singlet radical. These EPR signals could be accounted for by a pentadienyl radical and a strained allyl radical, respectively. Experiments using 11d-AA, 13(R)d-AA, 15d-AA, 13,15d(2)-AA, and octadeuterated AA (d(8)-AA) confirmed that the unpaired electron in the pentadienyl radical is delocalized over C11, C13, and C15. A 6-line EPR radical was observed when 16d(2)-AA was used, indicating only one strongly interacting C16 hydrogen. These results support a functional role for peroxide-generated tyrosyl radicals in lipoxygenase catalysis by ASA-PGHS-2 and also indicate that the AA radical in ASA-PGHS-2 is more constrained than the corresponding radical in native PGHS-2.
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Affiliation(s)
- Ah-lim Tsai
- Department of Internal Medicine, University of Texas Health Science Center at Houston, Houston, Texas 77030, USA.
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Affiliation(s)
- R P Pesavento
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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