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Preethi D, Anishetty S, Gautam P. Molecular dynamics study of in silico mutations in the auto-inhibitory loop of human endothelial nitric oxide synthase FMN sub-domain. J Mol Model 2021; 27:63. [PMID: 33527205 DOI: 10.1007/s00894-020-04643-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Accepted: 12/09/2020] [Indexed: 11/30/2022]
Abstract
Structural flexibility of the peptide linker connecting two domains is essential for the functioning of multi-domain complex. Nitric oxide synthase (NOS) isoforms contain the oxygenase and the reductase domains connected by calmodulin binding linker (CBL) region. Additionally, the endothelial NOS (eNOS) isoform contain an auto-inhibitory loop (AI) in the FMN reductase sub-domain which represses the inter-domain electron transfer process. Binding of Ca2+-Calmodulin complex on the CBL region relieves the AI loop repression and facilitates electron transfer from FMN in the reductase domain to the heme in the oxygenase domain. Few experimental studies have reported that in vitro mutation of Serine-615 (S615D) and Serine-633 (S633D) in the FMN reductase sub-domain to aspartic acid increased NO production and increased Ca2+ sensitivity. To understand the role of AI loop in eNOS repression and activation in serine mutants (S615D and S633D), we modelled the FMN reductase sub-domain of human eNOS protein with and without the CBL region. Molecular dynamics simulations performed indicated that the mutant protein AI loop structure was stabilized by salt bridge formed between D615 and R602. It was also found that mutation increased the flexibility of C-terminal residues of eNOS CBL region. The hinge-like movement of the AI loop allowed rotation of the FMN sub-domain clockwise which may favour electron-transfer in the mutant protein. This study provides insight on mutation (S615D and S633D) induced changes in AI loop and increased flexibility of CBL region which may lead to the protein activation and may also facilitate Calmodulin binding at physiological Ca2+ concentration. Graphical Abstract Mutation of amino acid residues contribute to structural changes at molecular level leading to alteration in protein dynamics and its function. Serine-615 and Serine-633 in the auto-inhibitory loop of human eNOS reductase model was mutated to aspartic acid in silico and molecular dynamics simulations of the protein showed that steric hindrance due to mutation altered the auto-inhibitory loop rearrangement and the FMN sub-domain movement favouring electron transfer.
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Affiliation(s)
- D Preethi
- Centre for Biotechnology, Anna University, Chennai, Tamil Nadu, 600 025, India
| | - Sharmila Anishetty
- Centre for Biotechnology, Anna University, Chennai, Tamil Nadu, 600 025, India.
| | - P Gautam
- Centre for Biotechnology, Anna University, Chennai, Tamil Nadu, 600 025, India. .,AU-KBC Research Centre, Anna University, Chennai, Tamil Nadu, 600 044, India.
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2
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Garcia V, Park EJ, Siragusa M, Frohlich F, Mahfuzul Haque M, Pascale JV, Heberlein KR, Isakson BE, Stuehr DJ, Sessa WC. Unbiased proteomics identifies plasminogen activator inhibitor-1 as a negative regulator of endothelial nitric oxide synthase. Proc Natl Acad Sci U S A 2020; 117:9497-9507. [PMID: 32300005 PMCID: PMC7196906 DOI: 10.1073/pnas.1918761117] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Nitric oxide (NO) produced by endothelial nitric oxide synthase (eNOS) is a critical mediator of vascular function. eNOS is tightly regulated at various levels, including transcription, co- and posttranslational modifications, and by various protein-protein interactions. Using stable isotope labeling with amino acids in cell culture (SILAC) and mass spectrometry (MS), we identified several eNOS interactors, including the protein plasminogen activator inhibitor-1 (PAI-1). In cultured human umbilical vein endothelial cells (HUVECs), PAI-1 and eNOS colocalize and proximity ligation assays demonstrate a protein-protein interaction between PAI-1 and eNOS. Knockdown of PAI-1 or eNOS eliminates the proximity ligation assay (PLA) signal in endothelial cells. Overexpression of eNOS and HA-tagged PAI-1 in COS7 cells confirmed the colocalization observations in HUVECs. Furthermore, the source of intracellular PAI-1 interacting with eNOS was shown to be endocytosis derived. The interaction between PAI-1 and eNOS is a direct interaction as supported in experiments with purified proteins. Moreover, PAI-1 directly inhibits eNOS activity, reducing NO synthesis, and the knockdown or antagonism of PAI-1 increases NO bioavailability. Taken together, these findings place PAI-1 as a negative regulator of eNOS and disruptions in eNOS-PAI-1 binding promote increases in NO production and enhance vasodilation in vivo.
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Affiliation(s)
- Victor Garcia
- Vascular Biology and Therapeutics Program, Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06520
| | - Eon Joo Park
- Vascular Biology and Therapeutics Program, Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06520
| | - Mauro Siragusa
- Institute for Vascular Signaling, Centre for Molecular Medicine, Goethe University, 60596 Frankfurt am Main, Germany
| | - Florian Frohlich
- Vascular Biology and Therapeutics Program, Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06520
- Department of Biology/Chemistry, Molecular Membrane Biology Section, University of Osnabrück, 49076 Osnabrück, Germany
| | - Mohammad Mahfuzul Haque
- Department of Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195
| | - Jonathan V Pascale
- Department of Pharmacology, New York Medical College, Valhalla, NY 10595
| | - Katherine R Heberlein
- Robert M. Berne Cardiovascular Research Center, University of Virginia School of Medicine, Charlottesville, VA 22908
| | - Brant E Isakson
- Robert M. Berne Cardiovascular Research Center, University of Virginia School of Medicine, Charlottesville, VA 22908
| | - Dennis J Stuehr
- Department of Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195
| | - William C Sessa
- Vascular Biology and Therapeutics Program, Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06520;
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3
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Zhao J, Yang HT, Wasala L, Zhang K, Yue Y, Duan D, Lai Y. Dystrophin R16/17 protein therapy restores sarcolemmal nNOS in trans and improves muscle perfusion and function. Mol Med 2019; 25:31. [PMID: 31266455 PMCID: PMC6607532 DOI: 10.1186/s10020-019-0101-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2019] [Accepted: 06/20/2019] [Indexed: 01/08/2023] Open
Abstract
Background Delocalization of neuronal nitric oxide synthase (nNOS) from the sarcolemma leads to functional muscle ischemia. This contributes to the pathogenesis in cachexia, aging and muscular dystrophy. Mutations in the gene encoding dystrophin result in Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD). In many BMD patients and DMD patients that have been converted to BMD by gene therapy, sarcolemmal nNOS is missing due to the lack of dystrophin nNOS-binding domain. Methods Dystrophin spectrin-like repeats 16 and 17 (R16/17) is the sarcolemmal nNOS localization domain. Here we explored whether R16/17 protein therapy can restore nNOS to the sarcolemma and prevent functional ischemia in transgenic mice which expressed an R16/17-deleted human micro-dystrophin gene in the dystrophic muscle. The palmitoylated R16/17.GFP fusion protein was conjugated to various cell-penetrating peptides and produced in the baculovirus-insect cell system. The best fusion protein was delivered to the transgenic mice and functional muscle ischemia was quantified. Results Among five candidate cell-penetrating peptides, the mutant HIV trans-acting activator of transcription (TAT) protein transduction domain (mTAT) was the best in transferring the R16/17.GFP protein to the muscle. Systemic delivery of the mTAT.R16/17.GFP protein to micro-dystrophin transgenic mice successfully restored sarcolemmal nNOS without inducing T cell infiltration. More importantly, R16/17 protein therapy effectively prevented treadmill challenge-induced force loss and improved muscle perfusion during contraction. Conclusions Our results suggest that R16/17 protein delivery is a highly promising therapy for muscle diseases involving sarcolemmal nNOS delocalizaton. Electronic supplementary material The online version of this article (10.1186/s10020-019-0101-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Junling Zhao
- Department of Molecular Microbiology and Immunology, School of Medicine, University of Missouri, Medical Sciences Building, One Hospital Drive, Columbia, MO, 65212, USA
| | - Hsiao Tung Yang
- Department of Biomedical Sciences, College of Veterinary Medicine, University of Missouri, Columbia, MO, 65212, USA
| | - Lakmini Wasala
- Department of Molecular Microbiology and Immunology, School of Medicine, University of Missouri, Medical Sciences Building, One Hospital Drive, Columbia, MO, 65212, USA
| | - Keqing Zhang
- Department of Molecular Microbiology and Immunology, School of Medicine, University of Missouri, Medical Sciences Building, One Hospital Drive, Columbia, MO, 65212, USA
| | - Yongping Yue
- Department of Molecular Microbiology and Immunology, School of Medicine, University of Missouri, Medical Sciences Building, One Hospital Drive, Columbia, MO, 65212, USA
| | - Dongsheng Duan
- Department of Molecular Microbiology and Immunology, School of Medicine, University of Missouri, Medical Sciences Building, One Hospital Drive, Columbia, MO, 65212, USA. .,Department of Biomedical Sciences, College of Veterinary Medicine, University of Missouri, Columbia, MO, 65212, USA. .,Department of Neurology, School of Medicine, University of Missouri, Columbia, MO, 65212, USA. .,Department of Bioengineering, University of Missouri, Columbia, MO, 65212, USA.
| | - Yi Lai
- Department of Molecular Microbiology and Immunology, School of Medicine, University of Missouri, Medical Sciences Building, One Hospital Drive, Columbia, MO, 65212, USA.
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4
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Stuehr DJ, Haque MM. Nitric oxide synthase enzymology in the 20 years after the Nobel Prize. Br J Pharmacol 2019; 176:177-188. [PMID: 30402946 PMCID: PMC6295403 DOI: 10.1111/bph.14533] [Citation(s) in RCA: 94] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Revised: 10/25/2018] [Accepted: 10/31/2018] [Indexed: 12/31/2022] Open
Abstract
This review briefly summarizes what was known about NOS enzymology at the time of the Nobel Prize award in 1998 and then discusses from the author's perspective some of the advances in NOS enzymology over the subsequent 20 years, focused on five aspects: the maturation process of NOS enzymes and its regulation; the mechanism of NO synthesis; the redox roles played by the 6R-tetrahydrobiopterin cofactor; the role of protein conformational behaviour in enabling NOS electron transfer and its regulation by NOS structural elements and calmodulin, and the catalytic cycling pathways of NOS enzymes and their influence on NOS activity. LINKED ARTICLES: This article is part of a themed section on Nitric Oxide 20 Years from the 1998 Nobel Prize. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.2/issuetoc.
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Affiliation(s)
- Dennis J Stuehr
- Department of Inflammation and Immunity, Lerner Research InstituteThe Cleveland ClinicClevelandOHUSA
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5
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Li J, Zheng H, Wang W, Miao Y, Sheng Y, Feng C. Role of an isoform-specific residue at the calmodulin-heme (NO synthase) interface in the FMN - heme electron transfer. FEBS Lett 2018; 592:2425-2431. [PMID: 29904908 DOI: 10.1002/1873-3468.13158] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Revised: 05/31/2018] [Accepted: 06/05/2018] [Indexed: 12/18/2022]
Abstract
The interface between calmodulin (CaM) and the NO synthase (NOS) heme domain is the least characterized interprotein interface that the NOS isoforms must traverse through during catalysis. Our previous molecular dynamics simulations predicted a salt bridge between K497 in human inducible NOS (iNOS) heme domain and D118(CaM). Herein, the FMN - heme interdomain electron transfer (IET) rate was found to be notably decreased by charge-reversal mutation, while the IET in the iNOS K497D mutant is significantly restored by the CaM D118K mutation. The results of wild-type protein with added synthetic peptides further demonstrate the critical nature of K497 relative to the rest of the peptide sequence in modulating the IET. These data provide definitive evidence supporting the regulatory role of the isoform-specific K497 residue.
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Affiliation(s)
- Jinghui Li
- College of Pharmacy, University of New Mexico, Albuquerque, NM, USA
| | - Huayu Zheng
- College of Pharmacy, University of New Mexico, Albuquerque, NM, USA.,Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM, USA
| | - Wei Wang
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM, USA
| | - Yubin Miao
- Department of Radiology, School of Medicine, University of Colorado Denver, Aurora, CO, USA
| | - Yinghong Sheng
- Department of Chemistry & Physics, College of Arts & Sciences, Florida Gulf Coast University, Fort Myers, FL, USA
| | - Changjian Feng
- College of Pharmacy, University of New Mexico, Albuquerque, NM, USA.,Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM, USA
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6
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Li J, Zheng H, Feng C. Deciphering mechanism of conformationally controlled electron transfer in nitric oxide synthases. FRONT BIOSCI-LANDMRK 2018; 23:1803-1821. [PMID: 29772530 PMCID: PMC11167721 DOI: 10.2741/4674] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Electron transfer is a fundamental process in life that is very often coupled to catalysis within redox enzymes through a stringent control of protein conformational movements. Mammalian nitric oxide synthase (NOS) proteins are redox flavo-hemoproteins consisting of multiple modular domains. The NOS enzyme is exquisitely regulated in vivo by its partner, the Ca2+ sensing protein calmodulin (CaM), to control production of nitric oxide (NO). The importance of functional domain motion in NOS regulation has been increasingly recognized. The significant size and flexibility of NOS is a tremendous challenge to the mechanistic studies. Herein recent applications of modern biophysical techniques to NOS problems have been critically analyzed. It is important to note that any current biophysical technique alone can only probe partial aspects of the conformational dynamics due to limitations in the technique itself and/or the sample preparations. It is necessary to combine the latest methods to comprehensively quantitate the key conformational aspects (conformational states and distribution, conformational change rates, and domain interacting interfaces) governing the electron transfer. This is to answer long-standing central questions about the NOS isoforms by defining how specific CaM-NOS interactions and regulatory elements underpin the distinct conformational behavior of the NOS isoform, which in turn determine unique electron transfer and NO synthesis properties. This review is not intended as comprehensive, but as a discussion of prospects that promise impact on important questions in the NOS enzymology field.
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Affiliation(s)
- Jinghui Li
- College of Pharmacy, University of New Mexico, Albuquerque, NM 87131, USA
| | - Huayu Zheng
- College of Pharmacy, University of New Mexico, Albuquerque, NM 87131, USA
| | - Changjian Feng
- University of New Mexico, MSC 09 5360, Albuquerque, NM 87131,
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7
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Hanson QM, Carley JR, Gilbreath TJ, Smith BC, Underbakke ES. Calmodulin-induced Conformational Control and Allostery Underlying Neuronal Nitric Oxide Synthase Activation. J Mol Biol 2018; 430:935-947. [PMID: 29458127 DOI: 10.1016/j.jmb.2018.02.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Revised: 02/07/2018] [Accepted: 02/07/2018] [Indexed: 10/18/2022]
Abstract
Nitric oxide synthase (NOS) is the primary generator of nitric oxide signals controlling diverse physiological processes such as neurotransmission and vasodilation. NOS activation is contingent on Ca2+/calmodulin binding at a linker between its oxygenase and reductase domains to induce large conformational changes that orchestrate inter-domain electron transfer. However, the structural dynamics underlying activation of full-length NOS remain ambiguous. Employing hydrogen-deuterium exchange mass spectrometry, we reveal mechanisms underlying neuronal NOS activation by calmodulin and regulation by phosphorylation. We demonstrate that calmodulin binding orders the junction between reductase and oxygenase domains, exposes the FMN subdomain, and elicits a more dynamic oxygenase active site. Furthermore, we demonstrate that phosphorylation partially mimics calmodulin activation to modulate neuronal NOS activity via long-range allostery. Calmodulin binding and phosphorylation ultimately promote a more dynamic holoenzyme while coordinating inter-domain communication and electron transfer.
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Affiliation(s)
- Quinlin M Hanson
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA
| | - Jeffrey R Carley
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA
| | - Tyler J Gilbreath
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA
| | - Brian C Smith
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Eric S Underbakke
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA.
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8
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Haque MM, Tejero J, Bayachou M, Kenney CT, Stuehr DJ. A cross-domain charge interaction governs the activity of NO synthase. J Biol Chem 2018; 293:4545-4554. [PMID: 29414777 DOI: 10.1074/jbc.ra117.000635] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2017] [Revised: 01/17/2018] [Indexed: 11/06/2022] Open
Abstract
NO synthase (NOS) enzymes perform interdomain electron transfer reactions during catalysis that may rely on complementary charge interactions at domain-domain interfaces. Guided by our previous results and a computer-generated domain-docking model, we assessed the importance of cross-domain charge interactions in the FMN-to-heme electron transfer in neuronal NOS (nNOS). We reversed the charge of three residues (Glu-762, Glu-816, and Glu-819) that form an electronegative triad on the FMN domain and then individually reversed the charges of three electropositive residues (Lys-423, Lys-620, and Lys-660) on the oxygenase domain (NOSoxy), to potentially restore a cross-domain charge interaction with the triad, but in reversed polarity. Charge reversal of the triad completely eliminated heme reduction and NO synthesis in nNOS. These functions were partly restored by the charge reversal at oxygenase residue Lys-423, but not at Lys-620 or Lys-660. Full recovery of heme reduction was probably muted by an accompanying change in FMN midpoint potential that made electron transfer to the heme thermodynamically unfavorable. Our results provide direct evidence that cross-domain charge pairing is required for the FMN-to-heme electron transfer in nNOS. The unique ability of charge reversal at position 423 to rescue function indicates that it participates in an essential cross-domain charge interaction with the FMN domain triad. This supports our domain-docking model and suggests that it may depict a productive electron transfer complex formed during nNOS catalysis.
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Affiliation(s)
- Mohammad Mahfuzul Haque
- From the Departments of Pathobiology, Lerner Research Institute, The Cleveland Clinic, Cleveland, Ohio 44195
| | - Jesús Tejero
- the Pittsburgh Heart, Lung, Blood, and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, and
| | - Mekki Bayachou
- the Department of Chemistry, Cleveland State University, Cleveland, Ohio 44115
| | - Claire T Kenney
- From the Departments of Pathobiology, Lerner Research Institute, The Cleveland Clinic, Cleveland, Ohio 44195
| | - Dennis J Stuehr
- From the Departments of Pathobiology, Lerner Research Institute, The Cleveland Clinic, Cleveland, Ohio 44195,
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9
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Dai Y, Haque MM, Stuehr DJ. Restricting the conformational freedom of the neuronal nitric-oxide synthase flavoprotein domain reveals impact on electron transfer and catalysis. J Biol Chem 2017; 292:6753-6764. [PMID: 28232486 DOI: 10.1074/jbc.m117.777219] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Revised: 02/16/2017] [Indexed: 01/02/2023] Open
Abstract
The signaling molecule nitric oxide (NO) is synthesized in animals by structurally related NO synthases (NOSs), which contain NADPH/FAD- and FMN-binding domains. During catalysis, NADPH-derived electrons transfer into FAD and then distribute into the FMN domain for further transfer to internal or external heme groups. Conformational freedom of the FMN domain is thought to be essential for the electron transfer (ET) reactions in NOSs. To directly examine this concept, we utilized a "Cys-lite" neuronal NOS flavoprotein domain and substituted Cys for two residues (Glu-816 and Arg-1229) forming a salt bridge between the NADPH/FAD and FMN domains in the conformationally closed structure to allow cross-domain disulfide bond formation or cross-linking by bismaleimides of various lengths. The disulfide bond cross-link caused a ≥95% loss of cytochrome c reductase activity that was reversible with DTT treatment, whereas graded cross-link lengthening gradually increased activity, thus defining the conformational constraints in the catalytic process. We used spectroscopic and stopped-flow techniques to further investigate how the changes in FMN domain conformational freedom impact the following: (i) the NADPH interaction; (ii) kinetics of electron loading (flavin reduction); (iii) stabilization of open versus closed conformational forms in two different flavin redox states; (iv) reactivity of the reduced FMN domain toward cytochrome c; (v) response to calmodulin binding; and (vi) the rates of interflavin ET and the FMN domain conformational dynamics. Together, our findings help explain how the spatial and temporal behaviors of the FMN domain impact catalysis by the NOS flavoprotein domain and how these behaviors are governed to enable electron flow through the enzyme.
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Affiliation(s)
- Yue Dai
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195 and.,the Department of Chemistry, Cleveland State University, Cleveland, Ohio 44115
| | - Mohammad Mahfuzul Haque
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195 and
| | - Dennis J Stuehr
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195 and
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10
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Ramasamy S, Haque MM, Gangoda M, Stuehr DJ. Tetrahydrobiopterin redox cycling in nitric oxide synthase: evidence supports a through-heme electron delivery. FEBS J 2016; 283:4491-4501. [PMID: 27760279 PMCID: PMC5387691 DOI: 10.1111/febs.13933] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Revised: 10/06/2016] [Accepted: 10/17/2016] [Indexed: 11/30/2022]
Abstract
The nitric oxide synthases (NOS) catalyze a two-step oxidation of l-arginine (Arg) to generate NO. In the first step, O2 activation involves one electron being provided to the heme by an enzyme-bound 6R-tetrahydro-l-biopterin cofactor (H4 B), and the H4 B radical must be reduced back to H4 B in order for NOS to continue catalysis. Although an NADPH-derived electron is used to reduce the H4 B radical, how this occurs is unknown. We hypothesized that the NOS flavoprotein domain might reduce the H4 B radical by utilizing the NOS heme porphyrin as a conduit to deliver the electron. This model predicts that factors influencing NOS heme reduction should also influence the extent and rate of H4 B radical reduction in kind. To test this, we utilized single catalytic turnover and stop-freeze methods, along with electron paramagnetic resonance spectroscopy, to measure the rate and extent of reduction of the 5-methyl-H4 B radical formed in neuronal NOS (nNOS) during Arg hydroxylation. We used several nNOS variants that supported either a slower or faster than normal rate of ferric heme reduction. We found that the rates and extents of nNOS heme reduction correlated well with the rates and extents of 5-methyl-H4 B radical reduction among the various nNOS enzymes. This supports a model where the heme porphyrin transfers an electron from the NOS flavoprotein to the H4 B radical formed during catalysis, revealing that the heme plays a dual role in catalyzing O2 activation or electron transfer at distinct points in the reaction cycle.
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Affiliation(s)
- Somasundaram Ramasamy
- Department of Pathobiology, Lerner Research Institute, The Cleveland Clinic, Cleveland, Ohio 44195, USA
| | - Mohammad Mahfuzul Haque
- Department of Pathobiology, Lerner Research Institute, The Cleveland Clinic, Cleveland, Ohio 44195, USA
| | - Mahinda Gangoda
- Department of Chemistry and Biochemistry, Kent State University, Kent, OH 44242, USA
| | - Dennis J. Stuehr
- Department of Pathobiology, Lerner Research Institute, The Cleveland Clinic, Cleveland, Ohio 44195, USA
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11
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Piazza M, Dieckmann T, Guillemette JG. Structural Studies of a Complex Between Endothelial Nitric Oxide Synthase and Calmodulin at Physiological Calcium Concentration. Biochemistry 2016; 55:5962-5971. [DOI: 10.1021/acs.biochem.6b00821] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Michael Piazza
- Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
| | - Thorsten Dieckmann
- Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
| | - J. Guy Guillemette
- Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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12
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Haque MM, Ray SS, Stuehr DJ. Phosphorylation Controls Endothelial Nitric-oxide Synthase by Regulating Its Conformational Dynamics. J Biol Chem 2016; 291:23047-23057. [PMID: 27613870 DOI: 10.1074/jbc.m116.737361] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2016] [Indexed: 11/06/2022] Open
Abstract
The activity of endothelial NO synthase (eNOS) is triggered by calmodulin (CaM) binding and is often further regulated by phosphorylation at several positions in the enzyme. Phosphorylation at Ser1179 occurs in response to diverse physiologic stimuli and increases the NO synthesis and cytochrome c reductase activities of eNOS, thereby enhancing its participation in biological signal cascades. Despite its importance, the mechanism by which Ser1179 phosphorylation increases eNOS activity is not understood. To address this, we used stopped-flow spectroscopy and computer modeling approaches to determine how the phosphomimetic mutation (S1179D) may impact electron flux through eNOS and the conformational behaviors of its reductase domain, both in the absence and presence of bound CaM. We found that S1179D substitution in CaM-free eNOS had multiple effects; it increased the rate of flavin reduction, altered the conformational equilibrium of the reductase domain, and increased the rate of its conformational transitions. We found these changes were equivalent in degree to those caused by CaM binding to wild-type eNOS, and the S1179D substitution together with CaM binding caused even greater changes in these parameters. The modeling indicated that the changes caused by the S1179D substitution, despite being restricted to the reductase domain, are sufficient to explain the stimulation of both the cytochrome c reductase and NO synthase activities of eNOS. This helps clarify how Ser1179 phosphorylation regulates eNOS and provides a foundation to compare its regulation by other phosphorylation events.
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Affiliation(s)
- Mohammad Mahfuzul Haque
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - Sougata Sinha Ray
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - Dennis J Stuehr
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
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13
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Wang ZQ, Haque MM, Binder K, Sharma M, Wei CC, Stuehr DJ. Engineering nitric oxide synthase chimeras to function as NO dioxygenases. J Inorg Biochem 2016; 158:122-130. [PMID: 27013266 DOI: 10.1016/j.jinorgbio.2016.03.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Revised: 03/10/2016] [Accepted: 03/12/2016] [Indexed: 10/22/2022]
Abstract
Nitric oxide synthases (NOSs) catalyze a two-step oxidation of l-arginine to form nitric oxide (NO) and l-citrulline. NOS contains a N-terminal oxygenase domain (NOSoxy) that is the site of NO synthesis, and a C-terminal reductase domain (NOSred) that binds nicotinamide adenine dinucleotide phosphate (NADPH), flavin adenine dinucleotide (FAD), and flavin mononucleotide (FMN) and provides electrons to the NOSoxy heme during catalysis. The three NOS isoforms in mammals inducible NOS (iNOS), neuronal NOS (nNOS), and endothelial NOS (eNOS) share high structural similarity but differ in NO release rates and catalytic properties due to differences in enzyme kinetic parameters. These parameters must be balanced for NOS enzymes to release NO, rather than consume it in a competing, inherent NO dioxygenase reaction. To improve understanding, we drew on a global catalytic model and previous findings to design three NOS chimeras that may predominantly function as NO dioxygenases: iNOSoxy/nNOSred (Wild type (WT) chimera), V346I iNOSoxy/nNOSred (V346I chimera) and iNOSoxy/S1412D nNOSred (S1412D chimera). The WT and S1412D chimeras had higher NO release than the parent iNOS, while the V346I chimera exhibited much lower NO release, consistent with expectations. Measurements indicated that a greater NO dioxygenase activity was achieved, particularly in the V346I chimera, which dioxygenated an estimated two to four NO per NO that it released, while the other chimeras had nearly equivalent NO dioxygenase and NO release activities. Computer simulations of the global catalytic model using the measured kinetic parameters produced results that mimicked the measured outcomes, and this provided further insights on the catalytic behaviors of the chimeras and basis of their increased NO dioxygenase activities.
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Affiliation(s)
- Zhi-Qiang Wang
- Department of Chemistry and Biochemistry, Kent State University Geauga, Burton, OH 44021, United States.
| | - Mohammad Mahfuzul Haque
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, United States
| | - Katherine Binder
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, United States
| | - Manisha Sharma
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, United States
| | - Chin-Chuan Wei
- Department of Chemistry, Southern Illinois University Edwardsville, Edwardsville, IL 62026, United States
| | - Dennis J Stuehr
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, United States.
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14
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Li Y, Xu J, Jiang F, Jiang Z, Liu C, Li L, Luo Y, Lu R, Mu Y, Liu Y, Xue B. G protein-coupled estrogen receptor is involved in modulating colonic motor function via nitric oxide release in C57BL/6 female mice. Neurogastroenterol Motil 2016; 28:432-42. [PMID: 26661936 DOI: 10.1111/nmo.12743] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Accepted: 11/02/2015] [Indexed: 12/17/2022]
Abstract
BACKGROUND Estrogen may regulate gastrointestinal motor functions, but the mechanism(s) is not totally understood. Here, we investigated whether G protein-coupled estrogen receptor (GPER/GPR30) was involved in regulating colonic motor functions and explored the underlying physiological mechanisms. METHODS Adult female C57BL/6 mice were used. The expression and localization of GPER were examined by RT-PCR, western blot, and immuno-labeling. The role of GPER in modulating colonic motor functions was assessed by the bead propulsion test in vivo and organ bath experiments in vitro. KEY RESULTS GPER was expressed in colonic myenteric neurons. The colonic transit time (CTT) in proestrus and estrus was significantly longer than that in diestrus. In vivo treatment with the selective GPER blocker G15 significantly shortened CTT in proestrus and estrus. In ovariectomized mice, acute estrogen supplementation increased CTT, which could be abolished by G15 co-administration. The GPER agonist G-1 caused a concentration-dependent inhibition of carbachol -induced circular muscle strips contraction, which was abolished by tetrodotoxin and the neuronal nitric oxide synthase (nNOS) inhibitor N-propyl-l-arginine. G-1 stimulated NO production in isolated longitudinal muscle myenteric plexus and cultured myenteric neurons, which was dependent on nNOS. Immunofluorescence labeling showed co-localization of GPER with nNOS in the myenteric plexus. CONCLUSIONS & INFERENCES We suggest that activation of GPER exerts an inhibitory effect on colonic motility by promoting NO release from myenteric nitrergic nerves. These results raise a possibility that GPER may be involved in mediating the inhibitory effect of estrogen on colonic motor functions, via a non-genomic, neurogenic mechanism.
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Affiliation(s)
- Y Li
- Department of Pathophysiology, Medical School, Shandong University, Jinan, China
| | - J Xu
- Department of Pathophysiology, Medical School, Shandong University, Jinan, China
| | - F Jiang
- Department of Pathophysiology, Medical School, Shandong University, Jinan, China
| | - Z Jiang
- Department of Pathophysiology, Medical School, Shandong University, Jinan, China
| | - C Liu
- Department of Physiology, Medical School, Shandong University, Jinan, China
| | - L Li
- Department of Pathophysiology, Medical School, Shandong University, Jinan, China
| | - Y Luo
- Department of Pathophysiology, Medical School, Shandong University, Jinan, China
| | - R Lu
- Department of Pathophysiology, Medical School, Shandong University, Jinan, China
| | - Y Mu
- Department of Pathophysiology, Medical School, Shandong University, Jinan, China
| | - Y Liu
- Department of Pathophysiology, Medical School, Shandong University, Jinan, China
| | - B Xue
- Department of Pathophysiology, Medical School, Shandong University, Jinan, China
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15
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Kaur P, Kiselar J, Yang S, Chance MR. Quantitative protein topography analysis and high-resolution structure prediction using hydroxyl radical labeling and tandem-ion mass spectrometry (MS). Mol Cell Proteomics 2015; 14:1159-68. [PMID: 25687570 DOI: 10.1074/mcp.o114.044362] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2014] [Indexed: 11/06/2022] Open
Abstract
Hydroxyl radical footprinting based MS for protein structure assessment has the goal of understanding ligand induced conformational changes and macromolecular interactions, for example, protein tertiary and quaternary structure, but the structural resolution provided by typical peptide-level quantification is limiting. In this work, we present experimental strategies using tandem-MS fragmentation to increase the spatial resolution of the technique to the single residue level to provide a high precision tool for molecular biophysics research. Overall, in this study we demonstrated an eightfold increase in structural resolution compared with peptide level assessments. In addition, to provide a quantitative analysis of residue based solvent accessibility and protein topography as a basis for high-resolution structure prediction; we illustrate strategies of data transformation using the relative reactivity of side chains as a normalization strategy and predict side-chain surface area from the footprinting data. We tested the methods by examination of Ca(+2)-calmodulin showing highly significant correlations between surface area and side-chain contact predictions for individual side chains and the crystal structure. Tandem ion based hydroxyl radical footprinting-MS provides quantitative high-resolution protein topology information in solution that can fill existing gaps in structure determination for large proteins and macromolecular complexes.
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Affiliation(s)
- Parminder Kaur
- From the ‡Center for Proteomics and Bioinformatics, Case Western Reserve University School of Medicine, 10009 Euclid Ave, Cleveland, Ohio, 44109
| | - Janna Kiselar
- From the ‡Center for Proteomics and Bioinformatics, Case Western Reserve University School of Medicine, 10009 Euclid Ave, Cleveland, Ohio, 44109
| | - Sichun Yang
- From the ‡Center for Proteomics and Bioinformatics, Case Western Reserve University School of Medicine, 10009 Euclid Ave, Cleveland, Ohio, 44109
| | - Mark R Chance
- From the ‡Center for Proteomics and Bioinformatics, Case Western Reserve University School of Medicine, 10009 Euclid Ave, Cleveland, Ohio, 44109
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16
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Sun W, Wang Z, Cao J, Wang X, Han Y, Ma Z. Enhanced production of nitric oxide in A549 cells through activation of TRPA1 ion channel by cold stress. Nitric Oxide 2014; 40:31-5. [PMID: 24815021 DOI: 10.1016/j.niox.2014.04.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2013] [Revised: 04/19/2014] [Accepted: 04/26/2014] [Indexed: 12/28/2022]
Abstract
The respiratory epithelium is exposed to the external environment, and inhalation of cold air is common during the season of winter. In addition, the lung is a major source of nitric oxide (NO). However, the effect of cold stress on the production of NO is still unclear. In the present work, We measured the change of NO in single cell with DACF-DA and the change in cytosolic Ca(2+) concentration ([Ca(2+)]c) in A549 cell. We observed that cold stress (from 20 °C to 5 °C) induced an increase of NO in A549 cell, which was completely abolished by applying an extracellular Ca(2+) free medium. Further experiments showed that cold-sensing transient receptor potential subfamily member 1 (TRPA1) channel agonist (allyl isothiocyanate, AITC) increased the production of NO and the level of [Ca(2+)]c in A549 cell. Additionally, TRPA1 inhibitor, Ruthenium red (RR) and camphor, significantly blocked the enhanced production of NO and the rise of [Ca(2+)]c induced by AITC or cold stimulation, respectively. Taken together, these data indicated that cold-induced TRPA1 activation was responsible for the enhanced production of NO in A549 cell.
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Affiliation(s)
- Wenwu Sun
- Department of Respiratory Medicine, General Hospital of Shenyang Military Area Command, Shenyang 110840, China
| | - Zhonghua Wang
- Department of Respiratory Medicine, General Hospital of Shenyang Military Area Command, Shenyang 110840, China
| | - Jianping Cao
- Department of Respiratory Medicine, General Hospital of Shenyang Military Area Command, Shenyang 110840, China
| | - Xu Wang
- Department of Experimental Medicine, Northern Hospital, Shenyang 110840, China
| | - Yaling Han
- Department of Cardiology, Institute of Cardiovascular Research of People's Liberation Army, Shenyang Northern Hospital, Shenyang 110840, China.
| | - Zhuang Ma
- Department of Respiratory Medicine, General Hospital of Shenyang Military Area Command, Shenyang 110840, China.
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17
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Yokom AL, Morishima Y, Lau M, Su M, Glukhova A, Osawa Y, Southworth DR. Architecture of the nitric-oxide synthase holoenzyme reveals large conformational changes and a calmodulin-driven release of the FMN domain. J Biol Chem 2014; 289:16855-65. [PMID: 24737326 DOI: 10.1074/jbc.m114.564005] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Nitric-oxide synthase (NOS) is required in mammals to generate NO for regulating blood pressure, synaptic response, and immune defense. NOS is a large homodimer with well characterized reductase and oxygenase domains that coordinate a multistep, interdomain electron transfer mechanism to oxidize l-arginine and generate NO. Ca(2+)-calmodulin (CaM) binds between the reductase and oxygenase domains to activate NO synthesis. Although NOS has long been proposed to adopt distinct conformations that alternate between interflavin and FMN-heme electron transfer steps, structures of the holoenzyme have remained elusive and the CaM-bound arrangement is unknown. Here we have applied single particle electron microscopy (EM) methods to characterize the full-length of the neuronal isoform (nNOS) complex and determine the structural mechanism of CaM activation. We have identified that nNOS adopts an ensemble of open and closed conformational states and that CaM binding induces a dramatic rearrangement of the reductase domain. Our three-dimensional reconstruction of the intact nNOS-CaM complex reveals a closed conformation and a cross-monomer arrangement with the FMN domain rotated away from the NADPH-FAD center, toward the oxygenase dimer. This work captures, for the first time, the reductase-oxygenase structural arrangement and the CaM-dependent release of the FMN domain that coordinates to drive electron transfer across the domains during catalysis.
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Affiliation(s)
- Adam L Yokom
- From the Department of Biological Chemistry, the Program in Chemical Biology, and
| | | | | | - Min Su
- the Life Sciences Institute, University of Michigan, Ann Arbor, Michigan 48109
| | | | | | - Daniel R Southworth
- From the Department of Biological Chemistry, the Life Sciences Institute, University of Michigan, Ann Arbor, Michigan 48109
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18
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Sobolewska-Stawiarz A, Leferink NGH, Fisher K, Heyes DJ, Hay S, Rigby SEJ, Scrutton NS. Energy landscapes and catalysis in nitric-oxide synthase. J Biol Chem 2014; 289:11725-11738. [PMID: 24610812 PMCID: PMC4002082 DOI: 10.1074/jbc.m114.548834] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Nitric oxide (NO) plays diverse roles in mammalian physiology. It is involved in blood pressure regulation, neurotransmission, and immune response, and is generated through complex electron transfer reactions catalyzed by NO synthases (NOS). In neuronal NOS (nNOS), protein domain dynamics and calmodulin binding are implicated in regulating electron flow from NADPH, through the FAD and FMN cofactors, to the heme oxygenase domain, the site of NO generation. Simple models based on crystal structures of nNOS reductase have invoked a role for large scale motions of the FMN-binding domain in shuttling electrons from the FAD-binding domain to the heme oxygenase domain. However, molecular level insight of the dynamic structural transitions in NOS enzymes during enzyme catalysis is lacking. We use pulsed electron-electron double resonance spectroscopy to derive inter-domain distance relationships in multiple conformational states of nNOS. These distance relationships are correlated with enzymatic activity through variable pressure kinetic studies of electron transfer and turnover. The binding of NADPH and calmodulin are shown to influence interdomain distance relationships as well as reaction chemistry. An important effect of calmodulin binding is to suppress adventitious electron transfer from nNOS to molecular oxygen and thereby preventing accumulation of reactive oxygen species. A complex landscape of conformations is required for nNOS catalysis beyond the simple models derived from static crystal structures of nNOS reductase. Detailed understanding of this landscape advances our understanding of nNOS catalysis/electron transfer, and could provide new opportunities for the discovery of small molecule inhibitors that bind at dynamic protein interfaces of this multidimensional energy landscape.
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Affiliation(s)
- Anna Sobolewska-Stawiarz
- From the Manchester Institute of Biotechnology and Faculty of Life Sciences, University of Manchester, Manchester M1 7DN, United Kingdom
| | - Nicole G H Leferink
- From the Manchester Institute of Biotechnology and Faculty of Life Sciences, University of Manchester, Manchester M1 7DN, United Kingdom
| | - Karl Fisher
- From the Manchester Institute of Biotechnology and Faculty of Life Sciences, University of Manchester, Manchester M1 7DN, United Kingdom
| | - Derren J Heyes
- From the Manchester Institute of Biotechnology and Faculty of Life Sciences, University of Manchester, Manchester M1 7DN, United Kingdom
| | - Sam Hay
- From the Manchester Institute of Biotechnology and Faculty of Life Sciences, University of Manchester, Manchester M1 7DN, United Kingdom
| | - Stephen E J Rigby
- From the Manchester Institute of Biotechnology and Faculty of Life Sciences, University of Manchester, Manchester M1 7DN, United Kingdom
| | - Nigel S Scrutton
- From the Manchester Institute of Biotechnology and Faculty of Life Sciences, University of Manchester, Manchester M1 7DN, United Kingdom.
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19
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Nitric oxide synthase domain interfaces regulate electron transfer and calmodulin activation. Proc Natl Acad Sci U S A 2013; 110:E3577-86. [PMID: 24003111 DOI: 10.1073/pnas.1313331110] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Nitric oxide (NO) produced by NO synthase (NOS) participates in diverse physiological processes such as vasodilation, neurotransmission, and the innate immune response. Mammalian NOS isoforms are homodimers composed of two domains connected by an intervening calmodulin-binding region. The N-terminal oxidase domain binds heme and tetrahydrobiopterin and the arginine substrate. The C-terminal reductase domain binds FAD and FMN and the cosubstrate NADPH. Although several high-resolution structures of individual NOS domains have been reported, a structure of a NOS holoenzyme has remained elusive. Determination of the higher-order domain architecture of NOS is essential to elucidate the molecular underpinnings of NO formation. In particular, the pathway of electron transfer from FMN to heme, and the mechanism through which calmodulin activates this electron transfer, are largely unknown. In this report, hydrogen-deuterium exchange mass spectrometry was used to map critical NOS interaction surfaces. Direct interactions between the heme domain, the FMN subdomain, and calmodulin were observed. These interaction surfaces were confirmed by kinetic studies of site-specific interface mutants. Integration of the hydrogen-deuterium exchange mass spectrometry results with computational docking resulted in models of the NOS heme and FMN subdomain bound to calmodulin. These models suggest a pathway for electron transfer from FMN to heme and a mechanism for calmodulin activation of this critical step.
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20
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Panda SP, Polusani SR, Kellogg DL, Venkatakrishnan P, Roman MG, Demeler B, Masters BSS, Roman LJ. Intra- and inter-molecular effects of a conserved arginine residue of neuronal and inducible nitric oxide synthases on FMN and calmodulin binding. Arch Biochem Biophys 2013; 533:88-94. [PMID: 23507581 DOI: 10.1016/j.abb.2013.03.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Revised: 03/06/2013] [Accepted: 03/07/2013] [Indexed: 10/27/2022]
Abstract
Nitric oxide synthases (NOSs) synthesize nitric oxide (NO), a signaling molecule, from l-arginine, utilizing electrons from NADPH. NOSs are flavo-hemo proteins, with two flavin molecules (FAD and FMN) and one heme per monomer, which require the binding of calcium/calmodulin (Ca(2+)/CaM) to produce NO. It is therefore important to understand the molecular factors influencing CaM binding from a structure/function perspective. A crystal structure of the CaM-bound iNOS FMN-binding domain predicted a salt bridge between R536 of human iNOS and E47 of CaM. To characterize the interaction between the homologous Arg of rat nNOS (R753) and murine iNOS (R530) with CaM, the Arg was mutated to Ala and, in iNOS, to Glu. The mutation weakens the interaction between nNOS and CaM, decreasing affinity by ~3-fold. The rate of electron transfer from FMN is greatly attenuated; however, little effect on electron transfer from FAD is observed. The mutated proteins showed reduced FMN binding, from 20% to 60%, suggesting an influence of this residue on FMN incorporation. The weakened FMN binding may be due to conformational changes caused by the arginine mutation. Our data show that this Arg residue plays an important role in CaM binding and influences FMN binding.
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Affiliation(s)
- Satya Prakash Panda
- Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
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21
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Iyanagi T, Xia C, Kim JJP. NADPH-cytochrome P450 oxidoreductase: prototypic member of the diflavin reductase family. Arch Biochem Biophys 2012; 528:72-89. [PMID: 22982532 PMCID: PMC3606592 DOI: 10.1016/j.abb.2012.09.002] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2012] [Revised: 09/01/2012] [Accepted: 09/03/2012] [Indexed: 12/31/2022]
Abstract
NADPH-cytochrome P450 oxidoreductase (CYPOR) and nitric oxide synthase (NOS), two members of the diflavin oxidoreductase family, are multi-domain enzymes containing distinct FAD and FMN domains connected by a flexible hinge. FAD accepts a hydride ion from NADPH, and reduced FAD donates electrons to FMN, which in turn transfers electrons to the heme center of cytochrome P450 or NOS oxygenase domain. Structural analysis of CYPOR, the prototype of this enzyme family, has revealed the exact nature of the domain arrangement and the role of residues involved in cofactor binding. Recent structural and biophysical studies of CYPOR have shown that the two flavin domains undergo large domain movements during catalysis. NOS isoforms contain additional regulatory elements within the reductase domain that control electron transfer through Ca(2+)-dependent calmodulin (CaM) binding. The recent crystal structure of an iNOS Ca(2+)/CaM-FMN construct, containing the FMN domain in complex with Ca(2+)/CaM, provided structural information on the linkage between the reductase and oxgenase domains of NOS, making it possible to model the holo iNOS structure. This review summarizes recent advances in our understanding of the dynamics of domain movements during CYPOR catalysis and the role of the NOS diflavin reductase domain in the regulation of NOS isozyme activities.
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Affiliation(s)
- Takashi Iyanagi
- Department of Biochemistry, Medical College of Wisconsin, USA
- Department of Life Science, The Himeji Institute of Technology, University of Hyogo, Japan
| | - Chuanwu Xia
- Department of Biochemistry, Medical College of Wisconsin, USA
| | - Jung-Ja P. Kim
- Department of Biochemistry, Medical College of Wisconsin, USA
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22
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Haque MM, Fadlalla MA, Aulak KS, Ghosh A, Durra D, Stuehr DJ. Control of electron transfer and catalysis in neuronal nitric-oxide synthase (nNOS) by a hinge connecting its FMN and FAD-NADPH domains. J Biol Chem 2012; 287:30105-16. [PMID: 22722929 PMCID: PMC3436266 DOI: 10.1074/jbc.m112.339697] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2012] [Revised: 06/13/2012] [Indexed: 01/19/2023] Open
Abstract
In nitric-oxide synthases (NOSs), two flexible hinges connect the FMN domain to the rest of the enzyme and may guide its interactions with partner domains for electron transfer and catalysis. We investigated the role of the FMN-FAD/NADPH hinge in rat neuronal NOS (nNOS) by constructing mutants that either shortened or lengthened this hinge by 2, 4, and 6 residues. Shortening the hinge progressively inhibited electron flux through the calmodulin (CaM)-free and CaM-bound nNOS to cytochrome c, whereas hinge lengthening relieved repression of electron flux in CaM-free nNOS and had no impact or slowed electron flux through CaM-bound nNOS to cytochrome c. How hinge length influenced heme reduction depended on whether enzyme flavins were pre-reduced with NADPH prior to triggering heme reduction. Without pre-reduction, changing the hinge length was deleterious; with pre-reduction, the hinge shortening was deleterious, and hinge lengthening increased heme reduction rates beyond wild type. Flavin fluorescence and stopped-flow kinetic studies on CaM-bound enzymes suggested hinge lengthening slowed the domain-domain interaction needed for FMN reduction. All hinge length changes lowered NO synthesis activity and increased uncoupled NADPH consumption. We conclude that several aspects of catalysis are sensitive to FMN-FAD/NADPH hinge length and that the native hinge allows a best compromise among the FMN domain interactions and associated electron transfer events to maximize NO synthesis and minimize uncoupled NADPH consumption.
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Affiliation(s)
- Mohammad Mahfuzul Haque
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - Mohammed A. Fadlalla
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - Kulwant S. Aulak
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - Arnab Ghosh
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - Deborah Durra
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - Dennis J. Stuehr
- From the Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
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23
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Lobe-specific calcium binding in calmodulin regulates endothelial nitric oxide synthase activation. PLoS One 2012; 7:e39851. [PMID: 22768143 PMCID: PMC3387242 DOI: 10.1371/journal.pone.0039851] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Accepted: 05/31/2012] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Human endothelial nitric oxide synthase (eNOS) requires calcium-bound calmodulin (CaM) for electron transfer but the detailed mechanism remains unclear. METHODOLOGY/PRINCIPAL FINDINGS Using a series of CaM mutants with E to Q substitution at the four calcium-binding sites, we found that single mutation at any calcium-binding site (B1Q, B2Q, B3Q and B4Q) resulted in ∼2-3 fold increase in the CaM concentration necessary for half-maximal activation (EC50) of citrulline formation, indicating that each calcium-binding site of CaM contributed to the association between CaM and eNOS. Citrulline formation and cytochrome c reduction assays revealed that in comparison with nNOS or iNOS, eNOS was less stringent in the requirement of calcium binding to each of four calcium-binding sites. However, lobe-specific disruption with double mutations in calcium-binding sites either at N- (B12Q) or at C-terminal (B34Q) lobes greatly diminished both eNOS oxygenase and reductase activities. Gel mobility shift assay and flavin fluorescence measurement indicated that N- and C-lobes of CaM played distinct roles in regulating eNOS catalysis; the C-terminal EF-hands in its calcium-bound form was responsible for the binding of canonical CaM-binding domain, while N-terminal EF-hands in its calcium-bound form controlled the movement of FMN domain. Limited proteolysis studies further demonstrated that B12Q and B34Q induced different conformational change in eNOS. CONCLUSIONS Our results clearly demonstrate that CaM controls eNOS electron transfer primarily through its lobe-specific calcium binding.
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24
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Li W, Fan W, Chen L, Elmore BO, Piazza M, Guillemette JG, Feng C. Role of an isoform-specific serine residue in FMN-heme electron transfer in inducible nitric oxide synthase. J Biol Inorg Chem 2012; 17:675-85. [PMID: 22407542 DOI: 10.1007/s00775-012-0887-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Accepted: 02/26/2012] [Indexed: 01/30/2023]
Abstract
In the crystal structure of a calmodulin (CaM)-bound FMN domain of human inducible nitric oxide synthase (NOS), the CaM-binding region together with CaM forms a hinge, and pivots on an R536(NOS)/E47(CaM) pair (Xia et al. J Biol Chem 284:30708-30717, 2009). Notably, isoform-specific human inducible NOS S562 and C563 residues form hydrogen bonds with the R536 residue through their backbone oxygens. In this study, we investigated the roles of the S562 and C563 residues in the NOS FMN-heme interdomain electron transfer (IET), the rates of which can be used to probe the interdomain FMN/heme alignment. Human inducible NOS S562K and C563R mutants of an oxygenase/FMN (oxyFMN) construct were made by introducing charged residues at these sites as found in human neuronal NOS and endothelial NOS isoforms, respectively. The IET rate constant of the S562K mutant is notably decreased by one third, and its flavin fluorescence intensity per micromole per liter is diminished by approximately 24 %. These results suggest that a positive charge at position 562 destabilizes the hydrogen-bond-mediated NOS/CaM alignment, resulting in slower FMN-heme IET in the mutant. On the other hand, the IET rate constant of the C563R mutant is similar to that of the wild-type, indicating that the mutational effect is site-specific. Moreover, the human inducible NOS oxyFMN R536E mutant was constructed to disrupt the bridging CaM/NOS interaction, and its FMN-heme IET rate was decreased by 96 %. These results demonstrated a new role of the isoform-specific serine residue of the key CaM/FMN(NOS) bridging site in regulating the FMN-heme IET (possibly by tuning the alignment of the FMN and heme domains).
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Affiliation(s)
- Wenbing Li
- Department of Pharmaceutical Sciences, College of Pharmacy, University of New Mexico, Albuquerque, NM 87131, USA
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25
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Feng C. Mechanism of Nitric Oxide Synthase Regulation: Electron Transfer and Interdomain Interactions. Coord Chem Rev 2012; 256:393-411. [PMID: 22523434 PMCID: PMC3328867 DOI: 10.1016/j.ccr.2011.10.011] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Nitric oxide synthase (NOS), a flavo-hemoprotein, tightly regulates nitric oxide (NO) synthesis and thereby its dual biological activities as a key signaling molecule for vasodilatation and neurotransmission at low concentrations, and also as a defensive cytotoxin at higher concentrations. Three NOS isoforms, iNOS, eNOS and nNOS (inducible, endothelial, and neuronal NOS), achieve their key biological functions by tight regulation of interdomain electron transfer (IET) process via interdomain interactions. In particular, the FMN-heme IET is essential in coupling electron transfer in the reductase domain with NO synthesis in the heme domain by delivery of electrons required for O(2) activation at the catalytic heme site. Compelling evidence indicates that calmodulin (CaM) activates NO synthesis in eNOS and nNOS through a conformational change of the FMN domain from its shielded electron-accepting (input) state to a new electron-donating (output) state, and that CaM is also required for proper alignment of the domains. Another exciting recent development in NOS enzymology is the discovery of importance of the the FMN domain motions in modulating reactivity and structure of the catalytic heme active site (in addition to the primary role of controlling the IET processes). In the absence of a structure of full-length NOS, an integrated approach of spectroscopic (e.g. pulsed EPR, MCD, resonance Raman), rapid kinetics (laser flash photolysis and stopped flow) and mutagenesis methods is critical to unravel the molecular details of the interdomain FMN/heme interactions. This is to investigate the roles of dynamic conformational changes of the FMN domain and the docking between the primary functional FMN and heme domains in regulating NOS activity. The recent developments in understanding of mechanisms of the NOS regulation that are driven by the combined approach are the focuses of this review. An improved understanding of the role of interdomain FMN/heme interaction and CaM binding may serve as the basis for the design of new selective inhibitors of NOS isoforms.
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Affiliation(s)
- Changjian Feng
- Department of Pharmaceutical Sciences, University of New Mexico, Albuquerque, NM 87131 (USA) , Tel: 505-925-4326
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Haque MM, Kenney C, Tejero J, Stuehr DJ. A kinetic model linking protein conformational motions, interflavin electron transfer and electron flux through a dual-flavin enzyme-simulating the reductase activity of the endothelial and neuronal nitric oxide synthase flavoprotein domains. FEBS J 2011; 278:4055-69. [PMID: 21848659 DOI: 10.1111/j.1742-4658.2011.08310.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
NADPH-dependent dual-flavin enzymes provide electrons in many redox reactions, although the mechanism responsible for regulating their electron flux remains unclear. We recently proposed a four-state kinetic model that links the electron flux through a dual-flavin enzyme to its rates of interflavin electron transfer and FMN domain conformational motion [Stuehr DJ et al. (2009) FEBS J276, 3959-3974]. In the present study, we ran computer simulations of the kinetic model to determine whether it could fit the experimentally-determined, pre-steady-state and steady-state traces of electron flux through the neuronal and endothelial NO synthase flavoproteins (reductase domains of neuronal nitric oxide synthase and endothelial nitric oxide synthase, respectively) to cytochrome c. We found that the kinetic model accurately fitted the experimental data. The simulations gave estimates for the ensemble rates of interflavin electron transfer and FMN domain conformational motion in the reductase domains of neuronal nitric oxide synthase and endothelial nitric oxide synthase, provided the minimum rate boundary values, and predicted the concentrations of the four enzyme species that cycle during catalysis. The findings of the present study suggest that the rates of interflavin electron transfer and FMN domain conformational motion are counterbalanced such that both processes may limit electron flux through the enzymes. Such counterbalancing would allow a robust electron flux at the same time as keeping the rates of interflavin electron transfer and FMN domain conformational motion set at relatively slow levels.
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Affiliation(s)
- Mohammad M Haque
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, OH 44195, USA
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Wu G, Berka V, Tsai AL. Binding kinetics of calmodulin with target peptides of three nitric oxide synthase isozymes. J Inorg Biochem 2011; 105:1226-37. [PMID: 21763233 DOI: 10.1016/j.jinorgbio.2011.06.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2011] [Revised: 05/09/2011] [Accepted: 06/15/2011] [Indexed: 11/17/2022]
Abstract
Efficient electron transfer from reductase domain to oxygenase domain in nitric oxide synthase (NOS) is dependent on the binding of calmodulin (CaM). Rate constants for the binding of CaM to NOS target peptides was only determined previously by surface plasmon resonance (SPR) (Biochemistry 35, 8742-8747, 1996) suggesting that the binding of CaM to NOSs is slow and does not support the fast electron transfer in NOSs measured in previous and this studies. To resolve this contradiction, the binding rates of holo Alexa 350 labeled T34C/T110W CaM (Alexa-CaM) to target peptides from three NOS isozymes were determined using fluorescence stopped-flow. All three target peptides exhibited fast k(on) constants at 4.5°C: 6.6×10(8)M(-1)s(-1) for nNOS(726-749), 2.9×10(8)M(-1)s(-1) for eNOS(492-511) and 6.1×10(8)M(-1)s(-1) for iNOS(507-531), 3-4 orders of magnitude faster than those determined previously by SPR. Dissociation rates of NOS target peptides from Alexa-CaM/peptide complexes were measured by Ca(2+) chelation with ETDA: 3.7s(-1) for nNOS(726-749), 4.5s(-1) for eNOS(492-511), and 0.063s(-1) for iNOS(507-531). Our data suggest that the binding of CaM to NOS is fast and kinetically competent for efficient electron transfer and is unlikely rate-limiting in NOS catalysis. Only iNOS(507-531) was able to bind apo Alexa-CaM, but in a very different conformation from its binding to holo Alexa-CaM.
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Affiliation(s)
- Gang Wu
- Department of Internal Medicine, University of Texas Health Science Center at Houston, Houston, Texas 77030, USA.
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Feng C, Fan W, Dupont A, Guy Guillemette J, Ghosh DK, Tollin G. Electron transfer in a human inducible nitric oxide synthase oxygenase/FMN construct co-expressed with the N-terminal globular domain of calmodulin. FEBS Lett 2010; 584:4335-8. [PMID: 20868689 DOI: 10.1016/j.febslet.2010.09.028] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2010] [Revised: 09/16/2010] [Accepted: 09/16/2010] [Indexed: 11/26/2022]
Abstract
The FMN-heme intraprotein electron transfer (IET) kinetics in a human inducible NOS (iNOS) oxygenase/FMN (oxyFMN) construct co-expressed with NCaM, a truncated calmodulin (CaM) construct that includes only its N-terminal globular domain consisting of residues 1-75, were determined by laser flash photolysis. The IET rate constant is significantly decreased by nearly fourfold (compared to the iNOS oxyFMN co-expressed with full length CaM). This supports an important role of full length CaM in proper interdomain FMN/heme alignment in iNOS. The IET process was not observed with added excess EDTA, suggesting that Ca(2+) depletion results in the FMN domain moving away from the heme domain. The results indicate that a Ca(2+)-dependent reorganization of the truncated CaM construct could cause a major modification of the NCaM/iNOS association resulting in a loss of the IET.
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Affiliation(s)
- Changjian Feng
- College of Pharmacy, University of New Mexico, Albuquerque, NM 87131, USA.
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