1
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Campelo D, Lautier T, Urban P, Esteves F, Bozonnet S, Truan G, Kranendonk M. The Hinge Segment of Human NADPH-Cytochrome P450 Reductase in Conformational Switching: The Critical Role of Ionic Strength. Front Pharmacol 2017; 8:755. [PMID: 29163152 PMCID: PMC5670117 DOI: 10.3389/fphar.2017.00755] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2017] [Accepted: 10/04/2017] [Indexed: 11/18/2022] Open
Abstract
NADPH-cytochrome P450 reductase (CPR) is a redox partner of microsomal cytochromes P450 and is a prototype of the diflavin reductase family. CPR contains 3 distinct functional domains: a FMN-binding domain (acceptor reduction), a linker (hinge), and a connecting/FAD domain (NADPH oxidation). It has been demonstrated that the mechanism of CPR exhibits an important step in which it switches from a compact, closed conformation (locked state) to an ensemble of open conformations (unlocked state), the latter enabling electron transfer to redox partners. The conformational equilibrium between the locked and unlocked states has been shown to be highly dependent on ionic strength, reinforcing the hypothesis of the presence of critical salt interactions at the interface between the FMN and connecting FAD domains. Here we show that specific residues of the hinge segment are important in the control of the conformational equilibrium of CPR. We constructed six single mutants and two double mutants of the human CPR, targeting residues G240, S243, I245 and R246 of the hinge segment, with the aim of modifying the flexibility or the potential ionic interactions of the hinge segment. We measured the reduction of cytochrome c at various salt concentrations of these 8 mutants, either in the soluble or membrane-bound form of human CPR. All mutants were found capable of reducing cytochrome c yet with different efficiency and their maximal rates of cytochrome c reduction were shifted to lower salt concentration. In particular, residue R246 seems to play a key role in a salt bridge network present at the interface of the hinge and the connecting domain. Interestingly, the effects of mutations, although similar, demonstrated specific differences when present in the soluble or membrane-bound context. Our results demonstrate that the electrostatic and flexibility properties of the hinge segment are critical for electron transfer from CPR to its redox partners.
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Affiliation(s)
- Diana Campelo
- Center for Toxicogenomics and Human Health (ToxOmics), Genetics, Oncology and Human Toxicology, NOVA Medical School, Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisboa, Portugal
| | - Thomas Lautier
- LISBP, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France
| | - Philippe Urban
- LISBP, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France
| | - Francisco Esteves
- Center for Toxicogenomics and Human Health (ToxOmics), Genetics, Oncology and Human Toxicology, NOVA Medical School, Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisboa, Portugal
| | - Sophie Bozonnet
- LISBP, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France
| | - Gilles Truan
- LISBP, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France
| | - Michel Kranendonk
- Center for Toxicogenomics and Human Health (ToxOmics), Genetics, Oncology and Human Toxicology, NOVA Medical School, Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisboa, Portugal
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2
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Wang R, Wang B, Zheng B, Ma P, Gou R, Guo Y, Chen F, Li H, Wang Y, Pu J, Tang L. The FNR modules contribute to control nitric oxide synthase catalysis revealed by chimera enzymes. Mol Med Rep 2017; 16:9263-9269. [PMID: 29039476 DOI: 10.3892/mmr.2017.7745] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 09/28/2017] [Indexed: 11/05/2022] Open
Abstract
The reductase domains of neuronal NOS, endothelial NOS and two constitutive nitric oxide synthase (cNOS) share higher sequence similarity (>60%). In order to evaluate the role of ferredoxin‑NADP+ reductase (FNR) module in adjusting NOS catalytic activities, chimeras were by interchanging the FNR‑like module between endothelial NOS and neuronal NOS in the present study. The assays of steady‑state enzymatic activities for cytochrome c and ferricyanide reduction, NO synthesis and NADPH oxidation were performed spectrophotometrically. The two NOS FNR modules transferred their ferricyanide reductase character to the chimera enzymes. Results showed that the FNR module was important in adjusting electrons flow through the reductase domain and out of the FMN module. Results indicated that the FNR module was critical in controlling the electron transfer capacities of the FMN module.
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Affiliation(s)
- Ruiqiang Wang
- Department of Nephrology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Biyue Wang
- Department of Nephrology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Bowen Zheng
- Department of Nephrology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Pupu Ma
- Department of Nephrology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Rong Gou
- Department of Nephrology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Yuanyuan Guo
- Department of Nephrology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Fengmei Chen
- Department of Nephrology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Hua Li
- Department of Gerontology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Yi Wang
- Department of Gerontology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Juanjuan Pu
- Department of Gerontology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
| | - Lin Tang
- Department of Nephrology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, P.R. China
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3
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Costas-Insua C, Merino-Gracia J, Aicart-Ramos C, Rodríguez-Crespo I. Subcellular Targeting of Nitric Oxide Synthases Mediated by Their N-Terminal Motifs. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2017; 111:165-195. [PMID: 29459031 DOI: 10.1016/bs.apcsb.2017.07.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
From a catalytic point of view, the three mammalian nitric oxide synthases (NOSs) function in an almost identical way. The N-terminal oxygenase domain catalyzes the conversion of l-arginine to l-citrulline plus ·NO in two sequential oxidation steps. Once l-arginine binds to the active site positioned above the heme moiety, two consecutive monooxygenation reactions take place. In the first step, l-arginine is hydroxylated to make Nω-hydroxy-l-arginine in a process that requires 1 molecule of NADPH and 1 molecule of O2 per mol of l-arginine reacted. In the second step, Nω-hydroxy-l-arginine, never leaving the active site, is oxidized to ·NO plus l-citrulline and 1 molecule of O2 and 0.5 molecules of NADPH are consumed. Since nitric oxide is an important signaling molecule that participates in a number of biological processes, including neurotransmission, vasodilation, and immune response, synthesis and release of ·NO in vivo must be exquisitely regulated both in time and in space. Hence, NOSs have evolved introducing in their amino acid sequences subcellular targeting motifs, most of them located at their N-termini. Deletion studies performed on recombinant, purified NOSs have revealed that part of the N-terminus of all three NOS can be eliminated with the resulting mutant enzymes still being catalytically active. Likewise, NOS isoforms lacking part of their N-terminus when transfected in cells render mislocalized, active proteins. In this review we will comment on the current knowledge of these subcellular targeting signals present in nNOS, iNOS, and eNOS.
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4
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Aicart-Ramos C, Rodríguez-Crespo I. Binding of PDZ domains to the carboxy terminus of inducible nitric oxide synthase boosts electron transfer and NO synthesis. FEBS Lett 2015; 589:2207-12. [PMID: 26183564 DOI: 10.1016/j.febslet.2015.07.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2015] [Revised: 06/29/2015] [Accepted: 07/02/2015] [Indexed: 10/23/2022]
Abstract
iNOS lacks any phosphorylatable residue at its C-terminus despite displaying a 25-residue extension known to block electron transfer and activity. We report that C-terminal deletions of iNOS increased the cytochrome c reduction rate. Moreover, the interaction of the iNOS C-terminus with the PDZ domains of EBP50 or CAP70 resulted not only in augmented reductase activity and greater NO synthesis but also anticipated the formation of the air-stable semiquinone generated after NADPH addition. Hence, the C-terminus of iNOS regulates the activity of the enzyme, albeit, unlike nNOS and eNOS, displacement of the autoinhibitory element occurs upon binding to proteins with PDZ domains.
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Affiliation(s)
- Clara Aicart-Ramos
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040, Spain
| | - Ignacio Rodríguez-Crespo
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040, Spain.
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5
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Leferink NGH, Hay S, Rigby SEJ, Scrutton NS. Towards the free energy landscape for catalysis in mammalian nitric oxide synthases. FEBS J 2014; 282:3016-29. [PMID: 25491181 DOI: 10.1111/febs.13171] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2014] [Revised: 12/05/2014] [Accepted: 12/05/2014] [Indexed: 01/30/2023]
Abstract
The general requirement for conformational sampling in biological electron transfer reactions catalysed by multi-domain redox systems has been emphasized in recent years. Crucially, we lack insight into the extent of the conformational space explored and the nature of the energy landscapes associated with these reactions. The nitric oxide synthases (NOS) produce the signalling molecule NO through a series of complex electron transfer reactions. There is accumulating evidence that protein domain dynamics and calmodulin binding are implicated in regulating electron flow from NADPH, through the FAD and FMN cofactors, to the haem oxygenase domain, where NO is generated. Simple models based on static crystal structures of the isolated reductase domain have suggested a role for large-scale motions of the FMN-binding domain in shuttling electrons from the reductase domain to the oxygenase domain. However, detailed insight into the higher-order domain architecture and dynamic structural transitions in NOS enzymes during enzyme turnover is lacking. In this review, we discuss the recent advances made towards mapping the catalytic free energy landscapes of NOS enzymes through integration of both structural techniques (e.g. cryo-electron microscopy) and biophysical techniques (e.g. pulsed-electron paramagnetic resonance). The general picture that emerges from these experiments is that NOS enzymes exist in an equilibrium of conformations, comprising a 'rugged' or 'frustrated' energy landscape, with a key regulatory role for calmodulin in driving vectorial electron transfer by altering the conformational equilibrium. A detailed understanding of these landscapes may provide new opportunities for discovery of isoform-specific inhibitors that bind at the dynamic interfaces of these multi-dimensional energy landscapes.
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Affiliation(s)
- Nicole G H Leferink
- Manchester Institute of Biotechnology and Faculty of Life Sciences, The University of Manchester, UK
| | - Sam Hay
- Manchester Institute of Biotechnology and Faculty of Life Sciences, The University of Manchester, UK
| | - Stephen E J Rigby
- Manchester Institute of Biotechnology and Faculty of Life Sciences, The University of Manchester, UK
| | - Nigel S Scrutton
- Manchester Institute of Biotechnology and Faculty of Life Sciences, The University of Manchester, UK
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6
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Volkmann N, Martásek P, Roman LJ, Xu XP, Page C, Swift M, Hanein D, Masters BS. Holoenzyme structures of endothelial nitric oxide synthase - an allosteric role for calmodulin in pivoting the FMN domain for electron transfer. J Struct Biol 2014; 188:46-54. [PMID: 25175399 DOI: 10.1016/j.jsb.2014.08.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2014] [Accepted: 08/18/2014] [Indexed: 01/26/2023]
Abstract
While the three-dimensional structures of heme- and flavin-binding domains of the NOS isoforms have been determined, the structures of the holoenzymes remained elusive. Application of electron cryo-microscopy and structural modeling of the bovine endothelial nitric oxide synthase (eNOS) holoenzyme produced detailed models of the intact holoenzyme in the presence and absence of Ca(2+)/calmodulin (CaM). These models accommodate the cross-electron transfer from the reductase in one monomer to the heme in the opposite monomer. The heme domain acts as the anchoring dimeric structure for the entire enzyme molecule, while the FMN domain is activated by CaM to move flexibly to bridge the distance between the reductase and oxygenase domains. Our results indicate that the key regulatory role of CaM involves the stabilization of structural intermediates and precise positioning of the pivot for the FMN domain tethered shuttling motion to accommodate efficient and rapid electron transfer in the homodimer of eNOS.
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Affiliation(s)
- Niels Volkmann
- Bioinformatics and Systems Biology Program, Sanford Burnham Medical Research Institute, La Jolla, CA 92075, USA.
| | - Pavel Martásek
- Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA; Department of Pediatrics, First School of Medicine, Charles University, 12109 Prague, Czech Republic
| | - Linda J Roman
- Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
| | - Xiao-Ping Xu
- Bioinformatics and Systems Biology Program, Sanford Burnham Medical Research Institute, La Jolla, CA 92075, USA
| | - Christopher Page
- Bioinformatics and Systems Biology Program, Sanford Burnham Medical Research Institute, La Jolla, CA 92075, USA
| | - Mark Swift
- Bioinformatics and Systems Biology Program, Sanford Burnham Medical Research Institute, La Jolla, CA 92075, USA
| | - Dorit Hanein
- Bioinformatics and Systems Biology Program, Sanford Burnham Medical Research Institute, La Jolla, CA 92075, USA.
| | - Bettie Sue Masters
- Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
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7
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Panda SP, Li W, Venkatakrishnan P, Chen L, Astashkin AV, Masters BSS, Feng C, Roman LJ. Differential calmodulin-modulatory and electron transfer properties of neuronal nitric oxide synthase mu compared to the alpha variant. FEBS Lett 2013; 587:3973-8. [PMID: 24211446 DOI: 10.1016/j.febslet.2013.10.032] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2013] [Revised: 10/23/2013] [Accepted: 10/24/2013] [Indexed: 10/26/2022]
Abstract
Neuronal nitric oxide synthase μ (nNOSμ) contains 34 additional residues in an autoregulatory element compared to nNOSα. Cytochrome c and flavin reductions in the absence of calmodulin (CaM) were faster in nNOSμ than nNOSα, while rates in the presence of CaM were smaller. The magnitude of stimulation by CaM is thus notably lower in nNOSμ. No difference in NO production was observed, while electron transfer between the FMN and heme moieties and formation of an inhibitory ferrous-nitrosyl complex were slower in nNOSμ. Thus, the insert affects electron transfer rates, modulation of electron flow by CaM, and heme-nitrosyl complex formation.
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Affiliation(s)
- Satya P Panda
- Department of Biochemistry, University of Texas Health Science Center in San Antonio, San Antonio, TX 78229, USA
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8
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Feng C, Chen L, Li W, Elmore BO, Fan W, Sun X. Dissecting regulation mechanism of the FMN to heme interdomain electron transfer in nitric oxide synthases. J Inorg Biochem 2013; 130:130-40. [PMID: 24084585 DOI: 10.1016/j.jinorgbio.2013.09.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Revised: 08/12/2013] [Accepted: 09/05/2013] [Indexed: 11/25/2022]
Abstract
Nitric oxide synthase (NOS), a flavo-hemoprotein, is responsible for biosynthesis of nitric oxide (NO) in mammals. Three NOS isoforms, iNOS, eNOS and nNOS (inducible, endothelial, and neuronal NOS), achieve their biological functions by tight control of interdomain electron transfer (IET) process through 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 O2 activation at the catalytic heme site. Emerging evidence indicates that calmodulin (CaM) activates NO synthesis in eNOS and nNOS by 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 FMN and heme domains in the three NOS isoforms. In the absence of a structure of full-length NOS, an integrated approach of spectroscopic, rapid kinetic and mutagenesis methods is required to unravel regulation mechanism of the FMN-heme IET process. This is to investigate the roles of the FMN domain motions and the docking between the primary functional FMN and heme domains in regulating NOS activity. The recent developments in this area that are driven by the combined approach are the focuses of this review. A better understanding of the roles of interdomain FMN/heme interactions and CaM binding may serve as a basis for the rational design of new selective modulators of the NOS enzymes.
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Affiliation(s)
- Changjian Feng
- Department of Pharmaceutical Sciences, University of New Mexico, Albuquerque, NM 87131, USA.
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9
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Paulsen C, Carroll KS. Cysteine-mediated redox signaling: chemistry, biology, and tools for discovery. Chem Rev 2013; 113:4633-79. [PMID: 23514336 PMCID: PMC4303468 DOI: 10.1021/cr300163e] [Citation(s) in RCA: 815] [Impact Index Per Article: 74.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2012] [Indexed: 02/06/2023]
Affiliation(s)
- Candice
E. Paulsen
- Department of Chemistry, The Scripps Research
Institute, Jupiter, Florida, 33458, United States
| | - Kate S. Carroll
- Department of Chemistry, The Scripps Research
Institute, Jupiter, Florida, 33458, United States
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10
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Charge-pairing interactions control the conformational setpoint and motions of the FMN domain in neuronal nitric oxide synthase. Biochem J 2013; 450:607-17. [PMID: 23289611 DOI: 10.1042/bj20121488] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The NOS (nitric oxide synthase; EC 1.14.13.39) enzymes contain a C-terminal flavoprotein domain [NOSred (reductase domain of NOS)] that binds FAD and FMN, and an N-terminal oxygenase domain that binds haem. Evidence suggests that the FMN-binding domain undergoes large conformational motions to shuttle electrons between the NADPH/FAD-binding domain [FNR (ferredoxin NADP-reductase)] and the oxygenase domain. Previously we have shown that three residues on the FMN domain (Glu762, Glu816 and Glu819) that make charge-pairing interactions with the FNR help to slow electron flux through nNOSred (neuronal NOSred). In the present study, we show that charge neutralization or reversal at each of these residues alters the setpoint [Keq(A)] of the NOSred conformational equilibrium to favour the open (FMN-deshielded) conformational state. Moreover, computer simulations of the kinetic traces of cytochrome c reduction by the mutants suggest that they have higher conformational transition rates (1.5-4-fold) and rates of interflavin electron transfer (1.5-2-fold) relative to wild-type nNOSred. We conclude that the three charge-pairing residues on the FMN domain govern electron flux through nNOSred by stabilizing its closed (FMN-shielded) conformational state and by retarding the rate of conformational switching between its open and closed conformations.
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11
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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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12
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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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13
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Abstract
Diflavin reductases are essential proteins capable of splitting the two-electron flux from reduced pyridine nucleotides to a variety of one electron acceptors. The primary sequence of diflavin reductases shows a conserved domain organization harboring two catalytic domains bound to the FAD and FMN flavins sandwiched by one or several non-catalytic domains. The catalytic domains are analogous to existing globular proteins: the FMN domain is analogous to flavodoxins while the FAD domain resembles ferredoxin reductases. The first structural determination of one member of the diflavin reductases family raised some questions about the architecture of the enzyme during catalysis: both FMN and FAD were in perfect position for interflavin transfers but the steric hindrance of the FAD domain rapidly prompted more complex hypotheses on the possible mechanisms for the electron transfer from FMN to external acceptors. Hypotheses of domain reorganization during catalysis in the context of the different members of this family were given by many groups during the past twenty years. This review will address the recent advances in various structural approaches that have highlighted specific dynamic features of diflavin reductases.
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Affiliation(s)
- Louise Aigrain
- Gene Machines Group, Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK; E-Mail:
| | - Fataneh Fatemi
- Institut de Chimie des Substances Naturelles, CNRS, UPR 2301, Centre de Recherche de Gif, 1 Av. de la Terrasse, 91198 Gif-sur-Yvette Cedex, France; E-Mails: (F.F.); (O.F.); (E.L.)
| | - Oriane Frances
- Institut de Chimie des Substances Naturelles, CNRS, UPR 2301, Centre de Recherche de Gif, 1 Av. de la Terrasse, 91198 Gif-sur-Yvette Cedex, France; E-Mails: (F.F.); (O.F.); (E.L.)
| | - Ewen Lescop
- Institut de Chimie des Substances Naturelles, CNRS, UPR 2301, Centre de Recherche de Gif, 1 Av. de la Terrasse, 91198 Gif-sur-Yvette Cedex, France; E-Mails: (F.F.); (O.F.); (E.L.)
| | - Gilles Truan
- Université de Toulouse; INSA, UPS, INP; LISBP, 135 Avenue de Rangueil, F-31077 Toulouse, France
- INRA, UMR792 Ingénierie des Systèmes Biologiques et des Procédés, F-31400 Toulouse, France
- CNRS, UMR5504, F-31400 Toulouse, France
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +33-567048813; Fax: +33-567048814
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14
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Kaplánek R, Martásek P, Grüner B, Panda S, Rak J, Masters BSS, Král V, Roman LJ. Nitric oxide synthases activation and inhibition by metallacarborane-cluster-based isoform-specific affectors. J Med Chem 2012; 55:9541-8. [PMID: 23075390 DOI: 10.1021/jm300805x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A small library of boron-cluster- and metallacarborane-cluster-based ligands was designed, prepared, and tested for isoform-selective activation or inhibition of the three nitric oxide synthase isoforms. On the basis of the concept of creating a hydrophobic analogue of a natural substrate, a stable and nontoxic basic boron cluster system, previously used for boron neutron capture therapy, was modified by the addition of positively charged moieties to its periphery, providing hydrophobic and nonclassical hydrogen bonding interactions with the protein. Several of these compounds show efficacy for inhibition of NO synthesis with differential effects on the various nitric oxide synthase isoforms.
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Affiliation(s)
- Robert Kaplánek
- Department of Analytical Chemistry, Institute of Chemical Technology in Prague, Technická 5, 166 28 Prague 6, Czech Republic
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15
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Wang ZQ, Tejero J, Wei CC, Haque MM, Santolini J, Fadlalla M, Biswas A, Stuehr DJ. Arg375 tunes tetrahydrobiopterin functions and modulates catalysis by inducible nitric oxide synthase. J Inorg Biochem 2012; 108:203-15. [PMID: 22173094 PMCID: PMC3306459 DOI: 10.1016/j.jinorgbio.2011.11.015] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2011] [Revised: 11/12/2011] [Accepted: 11/14/2011] [Indexed: 10/15/2022]
Abstract
NO synthase enzymes (NOS) support unique single-electron transitions of a bound H(4)B cofactor during catalysis. Previous studies showed that both the pterin structure and surrounding protein residues impact H(4)B redox function during catalysis. A conserved Arg residue (Arg375 in iNOS) forms hydrogen bonds with the H(4)B ring. In order to understand the role of this residue in modulating the function of H(4)B and overall NO synthesis of the enzyme, we generated and characterized three mutants R375D, R375K and R375N of the oxygenase domain of inducible NOS (iNOSoxy). The mutations affected the dimer stability of iNOSoxy and its binding affinity toward substrates and H(4)B to varying degrees. Optical spectra of the ferric, ferrous, ferrous dioxy, ferrous-NO, ferric-NO, and ferrous-CO forms of each mutant were similar to the wild-type. However, mutants displayed somewhat lower heme midpoint potentials and faster ferrous heme-NO complex reactivity with O(2). Unlike the wild-type protein, mutants could not oxidize NOHA to nitrite in a H(2)O(2)-driven reaction. Mutation could potentially change the ferrous dioxy decay rate, H(4)B radical formation rate, and the amount of the Arg hydroxylation during single turnover Arg hydroxylation reaction. All mutants were able to form heterodimers with the iNOS G450A full-length protein and displayed lower NO synthesis activities and uncoupled NADPH consumption. We conclude that the conserved residue Arg375 (1) regulates the tempo and extent of the electron transfer between H(4)B and ferrous dioxy species and (2) controls the reactivity of the heme-based oxidant formed after electron transfer from H(4)B during steady state NO synthesis and H(2)O(2)-driven NOHA oxidation. Thus, Arg375 modulates the redox function of H(4)B and is important in controlling the catalytic function of NOS enzymes.
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Affiliation(s)
- Zhi-Qiang Wang
- Department of Chemistry and Biochemistry, Kent State University at Tuscarawas, New Philadelphia, Ohio, 44663
| | - Jesús Tejero
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio, 44195
| | - Chin-Chuan Wei
- Department of Chemistry, Southern Illinois University Edwardsville, Edwardsville, IL, 62026
| | - Mohammad Mahfuzul Haque
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio, 44195
| | - Jerome Santolini
- iBiTec-S; LSOD, C. E. A. Saclay; 91191 Gif-sur-Yvette Cedex, France
| | - Mohammed Fadlalla
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio, 44195
| | - Ashis Biswas
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio, 44195
| | - Dennis J. Stuehr
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio, 44195
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16
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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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17
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Smith BC, Fernhoff NB, Marletta MA. Mechanism and kinetics of inducible nitric oxide synthase auto-S-nitrosation and inactivation. Biochemistry 2012; 51:1028-40. [PMID: 22242685 DOI: 10.1021/bi201818c] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Nitric oxide (NO), the product of the nitric oxide synthase (NOS) reaction, was previously shown to result in S-nitrosation of the NOS Zn(2+)-tetrathiolate and inactivation of the enzyme. To probe the potential physiological significance of NOS S-nitrosation, we determined the inactivation time scale of the inducible NOS isoform (iNOS) and found it directly correlates with an increase in the level of iNOS S-nitrosation. A kinetic model of NOS inactivation in which arginine is treated as a suicide substrate was developed. In this model, NO synthesized at the heme cofactor is partitioned between release into solution (NO release pathway) and NOS S-nitrosation followed by NOS inactivation (inactivation pathway). Experimentally determined progress curves of NO formation were fit to the model. The NO release pathway was perturbed through addition of the NO traps oxymyoglobin (MbO(2)) and β2 H-NOX, which yielded partition ratios between NO release and inactivation of ~100 at 4 μM MbO(2) and ~22000 at saturating trap concentrations. The results suggest that a portion of the NO synthesized at the heme cofactor reacts with the Zn(2+)-tetrathiolate without being released into solution. Perturbation of the inactivation pathway through addition of the reducing agent GSH or TCEP resulted in a concentration-dependent decrease in the level of iNOS S-nitrosation that directly correlated with protection from iNOS inactivation. iNOS inactivation was most responsive to physiological concentrations of GSH with an apparent K(m) value of 13 mM. NOS turnover that leads to NOS S-nitrosation might be a mechanism for controlling NOS activity, and NOS S-nitrosation could play a role in the physiological generation of nitrosothiols.
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Affiliation(s)
- Brian C Smith
- California Institute for Quantitative Biosciences, University of California, Berkeley, California 94720-3220, United States
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18
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19
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Tejero J, Haque MM, Durra D, Stuehr DJ. A bridging interaction allows calmodulin to activate NO synthase through a bi-modal mechanism. J Biol Chem 2010; 285:25941-9. [PMID: 20529840 DOI: 10.1074/jbc.m110.126797] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calmodulin (CaM) activates the nitric-oxide synthases (NOS) by a mechanism that is not completely understood. A recent crystal structure showed that bound CaM engages in a bridging interaction with the NOS FMN subdomain. We investigated its importance in neuronal NOS (nNOS) by mutating the two residues that primarily create the bridging interaction (Arg(752) in the FMN subdomain and Glu(47) in CaM). Mutations designed to completely destroy the bridging interaction prevented bound CaM from increasing electron flux through the FMN subdomain and diminished the FMN-to-heme electron transfer by 90%, whereas mutations that partly preserve the interaction had intermediate effects. The bridging interaction appeared to control FMN subdomain interactions with both its electron donor (NADPH-FAD subdomain) and electron acceptor (heme domain) partner subdomains in nNOS. We conclude that the Arg(752)-Glu(47) bridging interaction is the main feature that enables CaM to activate nNOS. The mechanism is bi-modal and links a single structural aspect of CaM binding to specific changes in nNOS protein conformational and electron transfer properties that are essential for catalysis.
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Affiliation(s)
- Jesús Tejero
- Department of Pathobiology, Lerner Research Institute, The Cleveland Clinic, Cleveland, Ohio 44195, USA
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20
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Liu XD, Mazumdar T, Xu Y, Getzoff ED, Eissa NT. Identification of a flavin mononucleotide module residue critical for activity of inducible nitrite oxide synthase. THE JOURNAL OF IMMUNOLOGY 2009; 183:5977-82. [PMID: 19828635 DOI: 10.4049/jimmunol.0902274] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Inducible NO synthase (iNOS) contains an amino-terminal oxygenase domain, a carboxy-terminal reductase domain, and an intervening calmodulin-binding domain. For the synthesis of NO, iNOS is active as a homodimer formed by oxygenase domains, while the reductase domain is required to transfer electrons from NADPH. In this study, we identify glutamate 658 in the FMN domain of human iNOS to be a critical residue for iNOS activity and we explore the underlying mechanism for such role. Mutation of glutamate to aspartate almost abolished iNOS activity and reduced dimer formation. Substitution of this residue with noncharged alanine and glutamine, or positively charged lysine did not affect dimer formation and maintained around 60% of iNOS activity. These results suggest that the negative charge specific to glutamate plays an important role in iNOS activity.
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Affiliation(s)
- Xian-De Liu
- Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA
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21
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Xia C, Misra I, Iyanagi T, Kim JJP. Regulation of interdomain interactions by calmodulin in inducible nitric-oxide synthase. J Biol Chem 2009; 284:30708-17. [PMID: 19737939 DOI: 10.1074/jbc.m109.031682] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nitric-oxide synthases (NOSs) catalyze the conversion of l-arginine to nitric oxide and citrulline. There are three NOS isozymes, each with a different physiological role: neuronal NOS, endothelial NOS, and inducible NOS (iNOS). NOSs consist of an N-terminal oxygenase domain and a C-terminal reductase domain, linked by a calmodulin (CaM)-binding region. CaM is required for NO production, but unlike other NOS isozymes, iNOS binds CaM independently of the exogenous Ca(2+) concentration. We have co-expressed CaM and the FMN domain of human iNOS, which includes the CaM-binding region. The Ca(2+)-bound protein complex (CaCaMxFMN) forms an air-stable semiquinone when reduced with NADPH and reduces cytochrome c when reconstituted with the iNOS FAD/NADPH domain. We have solved the crystal structure of the CaCaMxFMN complex in four different conformations, each with a different relative orientation, between the FMN domain and the bound CaM. The CaM-binding region together with bound CaM forms a hinge, pivots on the conserved Arg(536), and regulates electron transfer from FAD to FMN and from FMN to heme by adjusting the relative orientation and distance among the three cofactors. In addition, the relative orientations of the N- and C-terminal lobes of CaM are also different among the four conformations, suggesting that the flexibility between the two halves of CaM also contributes to the fine tuning of the orientation/distance between the redox centers. The data demonstrate a possible mode for precise control of electron transfer by altering the distance and orientation of redox centers in a protein displaying domain movement.
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Affiliation(s)
- Chuanwu Xia
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
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22
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Stuehr DJ, Tejero J, Haque MM. Structural and mechanistic aspects of flavoproteins: electron transfer through the nitric oxide synthase flavoprotein domain. FEBS J 2009; 276:3959-74. [PMID: 19583767 DOI: 10.1111/j.1742-4658.2009.07120.x] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Nitric oxide synthases belong to a family of dual-flavin enzymes that transfer electrons from NAD(P)H to a variety of heme protein acceptors. During catalysis, their FMN subdomain plays a central role by acting as both an electron acceptor (receiving electrons from FAD) and an electron donor, and is thought to undergo large conformational movements and engage in two distinct protein-protein interactions in the process. This minireview summarizes what we know about the many factors regulating nitric oxide synthase flavoprotein domain function, primarily from the viewpoint of how they impact electron input/output and conformational behaviors of the FMN subdomain.
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Affiliation(s)
- Dennis J Stuehr
- Department of Pathobiology, Lerner Research Institute, Cleveland, OH 44195, USA.
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23
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Feng C, Tollin G. Regulation of interdomain electron transfer in the NOS output state for NO production. Dalton Trans 2009:6692-700. [PMID: 19690675 DOI: 10.1039/b902884f] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
There is still much that is unknown about how nitric oxide (NO) biosynthesis by NO synthase (NOS) isoform is tightly regulated at the molecular level. This is remarkable because deviated NO production in vivo has been implicated in an increasing number of diseases that currently lack effective treatments, including stroke and cancer. Given the significant public health burden of these diseases, the NOS enzyme family is a key target for development of new pharmaceuticals. Three NOS isoforms, inducible, endothelial and neuronal NOS (iNOS, eNOS and nNOS, respectively), achieve their key biological functions via stringent regulations of interdomain electron transfer (IET) processes. Unlike iNOS, eNOS and nNOS isoforms are controlled by calmodulin (CaM) binding through facilitating catalytically significant IET processes. The CaM-modulated NOS output state is an IET-competent complex between the flavin mononucleotide (FMN) domain and the catalytic heme domain. The output state facilitates the catalytically essential FMN-heme IET, and thereby enables NO production by NOS. Due to lack of reliable techniques for specifically determining the inter-domain FMN-heme interactions and their direct effects on the catalytic heme center, the molecular mechanism that underlies the output state formation remains elusive. The recent developments in our understanding of mechanisms of the NOS output state formation that are driven by a combination of molecular biology, laser flash photolysis, and spectroscopic techniques are the subject of this perspective.
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Affiliation(s)
- Changjian Feng
- College of Pharmacy, University of New Mexico, Albuquerque, NM 87131, USA.
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24
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Affiliation(s)
- Bettie Sue Siler Masters
- Department of Biochemistry, The University of Texas Health Science Center, San Antonio, Texas 78229, USA.
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25
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Fleming I. Biology of Nitric Oxide Synthases. Microcirculation 2008. [DOI: 10.1016/b978-0-12-374530-9.00003-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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26
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Nishino Y, Yamamoto K, Kimura S, Kikuchi A, Shiro Y, Iyanagi T. Mechanistic studies on the intramolecular one-electron transfer between the two flavins in the human endothelial NOS reductase domain. Arch Biochem Biophys 2007; 465:254-65. [PMID: 17610838 DOI: 10.1016/j.abb.2007.05.021] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2007] [Revised: 05/27/2007] [Accepted: 05/30/2007] [Indexed: 10/23/2022]
Abstract
The object of this study was to clarify the mechanism of electron transfer in the human endothelial nitric oxide synthase (eNOS) reductase domain using recombinant eNOS reductase domains; the FAD/NADPH domain containing FAD- and NADPH-binding sites and the FAD/FMN domain containing FAD/NADPH-, FMN-, and a calmodulin-binding sites. In the presence of molecular oxygen or menadione, the reduced FAD/NADPH domain is oxidized via the neutral (blue) semiquinone (FADH(*)), which has a characteristic absorption peak at 520 nm. The FAD/NADPH and FAD/FMN domains have high activity for ferricyanide, but the FAD/FMN domain has low activity for cytochrome c. In the presence or absence of calcium/calmodulin (Ca(2+)/CaM), reduction of the oxidized flavins (FAD-FMN) and air-stable semiquinone (FAD-FMNH(*)) with NADPH occurred in at least two phases in the absorbance change at 457nm. In the presence of Ca(2+)/CaM, the reduction rate of both phases was significantly increased. In contrast, an absorbance change at 596nm gradually increased in two phases, but the rate of the fast phase was decreased by approximately 50% of that in the presence of Ca(2+)/CaM. The air-stable semiquinone form was rapidly reduced by NADPH, but a significant absorbance change at 520 nm was not observed. These findings indicate that the conversion of FADH(2)-FMNH(*) to FADH(*)-FMNH(2) is unfavorable. Reduction of the FAD moiety is activated by CaM, but the formation rate of the active intermediate, FADH(*)-FMNH(2) is extremely low. These events could cause a lowering of enzyme activity in the catalytic cycle.
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Affiliation(s)
- Yoshitaka Nishino
- Graduate School of Life Science, Himeji Institute of Technology, University of Hyogo, Kouto 3-2-1, Kamigori, Hyogo 678-1297, Japan
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27
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Navarro-Lérida I, Martínez-Moreno M, Ventoso I, Álvarez-Barrientos A, Rodríguez-Crespo I. Binding of CAP70 to inducible nitric oxide synthase and implications for the vectorial release of nitric oxide in polarized cells. Mol Biol Cell 2007; 18:2768-77. [PMID: 17507652 PMCID: PMC1924814 DOI: 10.1091/mbc.e06-12-1102] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
In this article we analyze the mechanisms by which the C-terminal four amino acids of inducible nitric oxide synthase (NOS2) interact with proteins that contain PDZ (PSD-95/DLG/ZO-1) domains resulting in the translocation of NOS2 to the cellular apical domain. It has been reported that human hepatic NOS2 associates to EBP50, a protein with two PDZ domains present in epithelial cells. We describe herein that NOS2 binds through its four carboxy-terminal residues to CAP70, a protein that contains four PDZ modules that is targeted to apical membranes. Interestingly, this interaction augments both the cytochrome c reductase and .NO-synthase activities of NOS2. Binding of CAP70 to NOS2 also results in an increase in the population of active NOS2 dimers. In addition, CAP70 participates in the correct subcellular targeting of NOS2 in a process that is also dependent on the acylation state of the N-terminal end of NOS2. Hence, nonpalmitoylated NOS2 is unable to progress toward the apical side of the cell despite its interaction with either EBP50 or CAP70. Likewise, if we abrogate the interaction of NOS2 with either EBP50 or CAP70 by fusing the GFP reporter to the carboxy-terminal end of NOS2 palmitoylation is not sufficient to confer an apical targeting.
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Affiliation(s)
- Inmaculada Navarro-Lérida
- *Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - Mónica Martínez-Moreno
- *Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - Iván Ventoso
- Centro de Biología Molecular “Severo Ochoa,” Consejo Superior de Investigaciones Científicas-Universidad Autónoma, Facultad de Ciencias, Cantoblanco, Universidad Autónoma de Madrid, 28049 Madrid, Spain; and
| | | | - Ignacio Rodríguez-Crespo
- *Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
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Panda SP, Gao YT, Roman LJ, Martásek P, Salerno JC, Masters BSS. The role of a conserved serine residue within hydrogen bonding distance of FAD in redox properties and the modulation of catalysis by Ca2+/calmodulin of constitutive nitric-oxide synthases. J Biol Chem 2006; 281:34246-57. [PMID: 16966328 DOI: 10.1074/jbc.m601041200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The crystal structure of the neuronal nitric-oxide synthase (nNOS) NADPH/FAD binding domain indicated that Ser-1176 is within hydrogen bonding distance of Asp-1393 and the O4 atom of FAD and is also near the N5 atom of FAD (3.7 A). This serine residue is conserved in most of the ferredoxin-NADP+ reductase family of proteins and is important in electron transfer. In the present study, the homologous serines of both nNOS (Ser-1176) and endothelial nitric-oxide synthase (eNOS) (Ser-942) were mutated to threonine and alanine. Both substitutions yielded proteins that exhibited decreased rates of electron transfer through the flavin domains, in the presence and absence of Ca2+/CaM, as measured by reduction of potassium ferricyanide and cytochrome c. Rapid kinetics measurements of flavin reduction of all the mutants also showed a decrease in the rate of flavin reduction, in the absence and presence of Ca2+/CaM, as compared with the wild type proteins. The serine to alanine substitution caused both nNOS and eNOS to synthesize NO more slowly; however, the threonine mutants gave equal or slightly higher rates of NO production compared with the wild type enzymes. The midpoint redox potential measurements of all the redox centers revealed that wild type and threonine mutants of both nNOS and eNOS are very similar. However, the redox potentials of the FMN/FMNH* couple for alanine substitutions of both nNOS and eNOS are >100 mV higher than those of wild type proteins and are positive. These data presented here suggest that hydrogen bonding of the hydroxyl group of serine or threonine with the isoalloxazine ring of FAD and with the amino acids in its immediate milieu, particularly nNOS Asp-1393, affects the redox potentials of various flavin states, influencing the rate of electron transfer.
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Affiliation(s)
- Satya Prakash Panda
- Department of Biochemistry, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900, USA
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29
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Roman LJ, Masters BSS. Electron Transfer by Neuronal Nitric-oxide Synthase Is Regulated by Concerted Interaction of Calmodulin and Two Intrinsic Regulatory Elements. J Biol Chem 2006; 281:23111-8. [PMID: 16782703 DOI: 10.1074/jbc.m603671200] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The nitric-oxide synthases (NOSs) are modular, cofactor-containing enzymes, divided into a heme-containing oxygenase domain and an FMN- and FAD-containing reductase domain. The domains are connected by a calmodulin (CaM)-binding sequence, occupancy of which is required for nitric oxide (NO) production. Two additional CaM-modulated regulatory elements are present in the reductase domains of the constitutive isoforms, the autoregulatory region (AR) and the C-terminal tail region. Deletion of the AR reduces CaM stimulation of electron flow through the reductase domain from 10-fold in wild-type nNOS to 2-fold in the mutant. Deletion of the C terminus yields an enzyme with greatly enhanced reductase activity in the absence of CaM but with activity equivalent to that of wild-type enzyme in its presence. A mutant in which both the AR and C terminus were deleted completely loses CaM modulation through the reductase domain. Thus, transduction of the CaM effect through the reductase domain of nNOS is dependent on these elements. Formation of nitric oxide is, however, still stimulated by CaM in all three mutants. A CaM molecule in which the N-terminal lobe was replaced by the C-terminal lobe (CaM-CC) supported NO synthesis by the deletion mutants but not by wild-type nNOS. We propose a model in which the AR, the C-terminal tail, and CaM interact directly to regulate the conformational state of the reductase domain of nNOS.
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Affiliation(s)
- Linda J Roman
- Department of Biochemistry, the University of Texas Health Science Center, San Antonio, Texas 78229, USA.
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30
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Jones RJ, Gao YT, Simone TM, Salerno JC, Smith SME. NADPH analog binding to constitutive nitric oxide activates electron transfer and NO synthesis. Nitric Oxide 2006; 14:228-37. [PMID: 16412670 DOI: 10.1016/j.niox.2005.09.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2005] [Revised: 09/09/2005] [Accepted: 09/28/2005] [Indexed: 10/25/2022]
Abstract
We report here that NADPH analogs such as 2'5'ADP, ATP, and 2'AMP paradoxically activate constitutive calcium/calmodulin regulated nitric oxide synthases (cNOS), including the endothelial isoform (eNOS) and the neuronal isoform (nNOS). These activators compete with NADPH by filling the binding site of the adenine moiety of NADPH, but do not occupy the entire NADPH binding domain. Effects of these analogs on cNOS's include increasing the electron transfer rate to external acceptors, as assessed by cytochrome c reductase activity in the absence of calmodulin. In addition, NO synthase activity in the presence of calmodulin (with or without added calcium) was increased by the addition of NADPH analogs. In contrast, the same NADPH analogs inhibit iNOS, the calcium insensitive inducible isoform, which lacks control elements found in constitutive isoforms. Because ATP and ADP are among the effective activators of cNOS isoforms, these effects may be physiologically relevant.
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Affiliation(s)
- Rachel J Jones
- Biology Department, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
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31
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Masters BSS. The journey from NADPH-cytochrome P450 oxidoreductase to nitric oxide synthases. Biochem Biophys Res Commun 2005; 338:507-19. [PMID: 16246311 DOI: 10.1016/j.bbrc.2005.09.165] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2005] [Accepted: 09/29/2005] [Indexed: 11/17/2022]
Abstract
This mini-review will reflect the perspective of its author on two fields of research, which have merged as the result of the insights of investigators whose work has influenced both areas immeasurably. It cannot be overlooked, however, that the research activities of many during a period of over five decades have produced the chemical and biological bases for the exciting discoveries now encompassing the cytochromes P450 and their redox partners, and the three isoforms of nitric oxide synthase as they function in their respective biological milieux. Following the remarkable discovery that, indeed, molecular oxygen can be adducted to organic molecules by enzymatic systems and that such processes require a supply of reducing equivalents, it is the purpose of this review to provide a chart, with some of its detours, of the road that followed in the pursuit of interesting biological phenomena involving these two major oxygenation systems. It is not intended to be a balanced review and apologies must be offered in advance to those whose contributions may be overlooked or simply were not directly germane to the development of the author's journey.
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Affiliation(s)
- Bettie Sue Siler Masters
- Department of Biochemistry, The University of Texas Health Science Center at San Antonio, Texas 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
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Stuehr DJ, Wei CC, Wang Z, Hille R. Exploring the redox reactions between heme and tetrahydrobiopterin in the nitric oxide synthases. Dalton Trans 2005:3427-35. [PMID: 16234921 DOI: 10.1039/b506355h] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The NO synthases (NOSs) catalyze a two-step oxidation of L-arginine (Arg) to generate nitric oxide (NO) plus L-citrulline. Because NOSs are the only hemeproteins known to contain tetrahydrobiopterin (H4B) as a bound cofactor, the function and role of H4B in their heme-based oxygen activation and catalysis is of current interest. Distinct oxidative and reductive transitions of bound H4B cofactor occur during catalysis and are associated with distinct redox transitions of the NOS heme and flavin prosthetic groups. In this perspective, we discuss the redox transitions of H4B and heme with regard to their kinetics, regulation, role in the catalytic mechanism, and how and why they may be linked.
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Affiliation(s)
- Dennis J Stuehr
- Lerner Research Institute, Cleveland Clinic, Ohio State University, USA
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33
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Yamamoto K, Kimura S, Shiro Y, Iyanagi T. Interflavin one-electron transfer in the inducible nitric oxide synthase reductase domain and NADPH-cytochrome P450 reductase. Arch Biochem Biophys 2005; 440:65-78. [PMID: 16009330 DOI: 10.1016/j.abb.2005.05.027] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2005] [Revised: 05/26/2005] [Accepted: 05/30/2005] [Indexed: 10/25/2022]
Abstract
In this study, we have analyzed interflavin electron transfer reactions from FAD to FMN in both the full-length inducible nitric oxide synthase (iNOS) and its reductase domain. Comparison is made with the interflavin electron transfer in NADPH-cytochrome P450 reductase (CPR). For the analysis of interflavin electron transfer and the flavin intermediates observed during catalysis we have used menadione (MD), which can accept an electron from both the FAD and FMN sites of the enzyme. A characteristic absorption peak at 630 and 520 nm can identify each FAD and FMN semiquinone species, which is derived from CPR and iNOS, respectively. The charge transfer complexes of FAD with NADP+ or NADPH were monitored at 750 nm. In the presence of MD, the air-stable neutral (blue) semiquinone form (FAD-FMNH*) was observed as a major intermediate during the catalytic cycle in both the iNOS reductase domain and full-length enzyme, and its formation occurred without any lag phase indicating rapid interflavin electron transfer following the reduction of FAD by NADPH. These data also strongly suggest that the low level reactivity of a neutral (blue) FMN semiquinone radical with electron acceptors enables one-electron transfer in the catalytic cycle of both the FAD-FMN pairs in CPR and iNOS. On the basis of these data, we propose a common model for the catalytic cycle of both CaM-bound iNOS reductase domain and CPR.
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Affiliation(s)
- Keita Yamamoto
- Graduate School of Life Science, Himeji Institute of Technology, University of Hyogo, 3-2-1 Kouto, Kamigori-cho, Hyogo 678-1297, Japan
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34
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Jáchymová M, Martásek P, Panda S, Roman LJ, Panda M, Shea TM, Ishimura Y, Kim JJP, Masters BSS. Recruitment of governing elements for electron transfer in the nitric oxide synthase family. Proc Natl Acad Sci U S A 2005; 102:15833-8. [PMID: 16249336 PMCID: PMC1276075 DOI: 10.1073/pnas.0506522102] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
At least three building blocks are responsible for the molecular basis of the modulation of electron transfer in nitric oxide synthase (NOS) isoforms: the calmodulin-binding sequence, the C-terminal extension, and the autoregulatory loop in the reductase domain. We have attempted to impart the control conferred by the C termini of NOS to cytochrome P450 oxidoreductase (CYPOR), which contains none of these regulatory elements. The effect of these C termini on the properties of CYPOR sheds light on the possible evolutionary origin of NOS and addresses the recruitment of new peptides on the development of new functions for CYPOR. The C termini of NOSs modulate flavoprotein-mediated electron transfer to various electron acceptors. The reduction of the artificial electron acceptors cytochrome c, 2,6-dichlorophenolindophenol, and ferricyanide was inhibited by the addition of any of these C termini to CYPOR, whereas the reduction of molecular O(2) was increased. This suggests a shift in the rate-limiting step, indicating that the NOS C termini interrupt electron flux between flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) and/or the electron acceptors. The modulation of CYPOR by the addition of the NOS C termini is also supported by flavin reoxidation and fluorescence-quenching studies and antibody recognition of the C-terminal extension. These experiments support the origin of the NOS enzymes from modules consisting of a heme domain and CYPOR or ferredoxin-NADP(+) reductase- and flavodoxin-like subdomains that constitute CYPOR, followed by further recruitment of smaller modulating elements into the flavin-binding domains.
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Affiliation(s)
- M Jáchymová
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, TX 78229-3900, USA
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35
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Weaver J, Porasuphatana S, Tsai P, Pou S, Roman LJ, Rosen GM. A comparative study of neuronal and inducible nitric oxide synthases: generation of nitric oxide, superoxide, and hydrogen peroxide. Biochim Biophys Acta Gen Subj 2005; 1726:302-8. [PMID: 16216417 DOI: 10.1016/j.bbagen.2005.08.012] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2005] [Revised: 08/31/2005] [Accepted: 08/31/2005] [Indexed: 11/15/2022]
Abstract
Nitric oxide synthases (NOS) independent of the isozyme, produce nitric oxide (.NO), superoxide (O2.-), and hydrogen peroxide (H2O2). Since .NO has been implicated in many physiological processes, the importance of O2.- and H2O2 in regulating cell signaling by .NO cannot be overlooked. Before addressing these questions, we investigated the production of .NO, O2.-, and H2O2 by purified NOS. NOS 1 and NOS 2 were chosen, as the flux of .NO from each isozyme supports differential biological activity. We found that the initial rate and sustained production of .NO was considerably greater for NOS 2 as compared to NOS 1. In the absence of L-arginine, however, NOS 1 generation of O2.- and H2O2 was found to be substantially greater than that measured for NOS 2. Differences between NOS 1 and NOS 2 production of .NO, O2.-, and H2O2 may define the specific physiologic function of each isozyme.
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Affiliation(s)
- John Weaver
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, MD 21201, USA
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36
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Tiso M, Konas DW, Panda K, Garcin ED, Sharma M, Getzoff ED, Stuehr DJ. C-terminal tail residue Arg1400 enables NADPH to regulate electron transfer in neuronal nitric-oxide synthase. J Biol Chem 2005; 280:39208-19. [PMID: 16150731 DOI: 10.1074/jbc.m507775200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The neuronal nitric-oxide synthase (nNOS) flavoprotein domain (nNOSr) contains regulatory elements that repress its electron flux in the absence of bound calmodulin (CaM). The repression also requires bound NADP(H), but the mechanism is unclear. The crystal structure of a CaM-free nNOSr revealed an ionic interaction between Arg(1400) in the C-terminal tail regulatory element and the 2'-phosphate group of bound NADP(H). We tested the role of this interaction by substituting Ser and Glu for Arg(1400) in nNOSr and in the full-length nNOS enzyme. The CaM-free nNOSr mutants had cytochrome c reductase activities that were less repressed than in wild-type, and this effect could be mimicked in wild-type by using NADH instead of NADPH. The nNOSr mutants also had faster flavin reduction rates, greater apparent K(m) for NADPH, and greater rates of flavin auto-oxidation. Single-turnover cytochrome c reduction data linked these properties to an inability of NADP(H) to cause shielding of the FMN module in the CaM-free nNOSr mutants. The full-length nNOS mutants had no NO synthesis in the CaM-free state and had lower steady-state NO synthesis activities in the CaM-bound state compared with wild-type. However, the mutants had faster rates of ferric heme reduction and ferrous heme-NO complex formation. Slowing down heme reduction in R1400E nNOS with CaM analogues brought its NO synthesis activity back up to normal level. Our studies indicate that the Arg(1400)-2'-phosphate interaction is a means by which bound NADP(H) represses electron transfer into and out of CaM-free nNOSr. This interaction enables the C-terminal tail to regulate a conformational equilibrium of the FMN module that controls its electron transfer reactions in both the CaM-free and CaM-bound forms of nNOS.
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Affiliation(s)
- Mauro Tiso
- Department of Immunology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA
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37
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Konas DW, Zhu K, Sharma M, Aulak KS, Brudvig GW, Stuehr DJ. The FAD-shielding residue Phe1395 regulates neuronal nitric-oxide synthase catalysis by controlling NADP+ affinity and a conformational equilibrium within the flavoprotein domain. J Biol Chem 2004; 279:35412-25. [PMID: 15180983 DOI: 10.1074/jbc.m400872200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phe(1395) stacks parallel to the FAD isoalloxazine ring in neuronal nitric-oxide synthase (nNOS) and is representative of conserved aromatic amino acids found in structurally related flavoproteins. This laboratory previously showed that Phe(1395) was required to obtain the electron transfer properties and calmodulin (CaM) response normally observed in wild-type nNOS. Here we characterized the F1395S mutant of the nNOS flavoprotein domain (nNOSr) regarding its physical properties, NADP(+) binding characteristics, flavin reduction kinetics, steady-state and pre-steady-state cytochrome c reduction kinetics, and ability to shield its FMN cofactor in response to CaM or NADP(H) binding. F1395S nNOSr bound NADP(+) with 65% more of the nicotinamide ring in a productive conformation with FAD for hydride transfer and had an 8-fold slower rate of NADP(+) dissociation. CaM stimulated the rates of NADPH-dependent flavin reduction in wild-type nNOSr but not in the F1395S mutant, which had flavin reduction kinetics similar to those of CaM-free wild-type nNOSr. CaM-free F1395S nNOSr lacked repression of cytochrome c reductase activity that is typically observed in nNOSr. The combined results from pre-steady-state and EPR experiments revealed that this was associated with a lesser degree of FMN shielding in the NADP(+)-bound state as compared with wild type. We conclude that Phe(1395) regulates nNOSr catalysis in two ways. It facilitates NADP(+) release to prevent this step from being rate-limiting, and it enables NADP(H) to properly regulate a conformational equilibrium involving the FMN subdomain that controls reactivity of the FMN cofactor in electron transfer.
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Affiliation(s)
- David W Konas
- Department of Immunology, The Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA
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38
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Panda K, Adak S, Konas D, Sharma M, Stuehr DJ. A conserved aspartate (Asp-1393) regulates NADPH reduction of neuronal nitric-oxide synthase: implications for catalysis. J Biol Chem 2004; 279:18323-33. [PMID: 14966111 DOI: 10.1074/jbc.m310391200] [Citation(s) in RCA: 17] [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
Nitric-oxide synthases (NOSs) are flavo-heme enzymes whose electron transfer reactions are controlled by calmodulin (CaM). The NOS flavoprotein domain includes a ferredoxin-NADP(+) reductase (FNR)-like module that contains NADPH- and FAD-binding sites. FNR-like modules in related flavoproteins have three conserved residues that regulate electron transfer between bound NAD(P)H and FAD. To investigate the function of one of these residues in neuronal NOS (nNOS), we generated and characterized mutants that had Val, Glu, or Asn substituted for the conserved Asp-1393. All three mutants exhibited normal composition, spectral properties, and binding of cofactors, substrates, and CaM. All had slower NADPH-dependent cytochrome c and ferricyanide reductase activities, which were associated with proportionally slower rates of NADPH-dependent flavin reduction in the CaM-free and CaM-bound states. Rates of NO synthesis were also proportionally slower in the mutants and were associated with slower rates of CaM-dependent ferric heme reduction. However, a D1393V mutant whose flavins had been prereduced with NADPH had a normal rate of heme reduction. This indicated that the kinetic defect was restricted to flavin reduction step(s) in the mutants and suggested that this limited their catalytic activities. Together, our results show the following. 1) The presence and positioning of the Asp-1393 carboxylate side chain are critical to enable NADPH-dependent reduction of the nNOS flavoprotein. 2) Control of flavin reduction is important because it ensures that the rate of heme reduction is sufficiently fast to enable NO synthesis by nNOS.
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Affiliation(s)
- Koustubh Panda
- Department of Immunology, Lerner Research Institute, The Cleveland Clinic, Cleveland, Ohio 44195, USA
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39
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Chen PF, Wu KK. Structural elements contribute to the calcium/calmodulin dependence on enzyme activation in human endothelial nitric-oxide synthase. J Biol Chem 2003; 278:52392-400. [PMID: 14561757 DOI: 10.1074/jbc.m305469200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Two regions, located at residues 594-606/614-645 and residues 1165-1178, are present in the reductase domain of human endothelial nitric-oxide synthase (eNOS) but absent in its counterpart, inducible nitric-oxide synthase (iNOS). We previously demonstrated that removing residues 594-606/614-645 resulted in an enzyme (Delta45) containing an intrinsic calmodulin (CaM) purified from an Sf9/baculovirus expression system (Chen, P.-F., and Wu, K.K. (2000) J. Biol. Chem. 275, 13155-13163). Here we have further elucidated the differential requirement of Ca2+/CaM for enzyme activation between eNOS and iNOS by either deletion of residues 1165-1178 (Delta14) or combined deletions of residues 594-606/614-645 and 1165-1178 (Delta45/ Delta14) from eNOS to mimic iNOS. We measured the catalytic rates using purified proteins completely free of CaM. Steady-state analysis indicated that the Delta45 supported NO synthesis in the absence of CaM at 60% of the rate in its presence, consistent with our prior result that CaM-bound Delta45 retained 60% of its activity in the presence of 10 mm EGTA. Mutant Delta14 displayed a 1.5-fold reduction of EC50 for Ca2+/CaM-dependence in l-citrulline formation, and a 2-4-fold increase in the rates of NO synthesis, NADPH oxidation, and cytochrome c reduction relative to the wild type. The basal rates of double mutant Delta45/Delta14 in NO production, NADPH oxidation, and cytochrome c reduction were 3-fold greater than those of CaM-stimulated wild-type eNOS. Interestingly, all three activities of Delta45/ Delta14 were suppressed rather than enhanced by Ca2+/CaM, indicating a complete Ca2+/CaM independence for those reactions. The results suggest that the Ca2+/CaM-dependent catalytic activity of eNOS appears to be conferred mainly by these two structural elements, and the interdomain electron transfer from reductase to oxygenase domain does not require Ca2+/CaM when eNOS lacks these two segments.
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Affiliation(s)
- Pei-Feng Chen
- Vascular Biology Research Center and Division of Hematology, Department of Internal Medicine, The University of Texas Health Science Center at Houston, Houston, Texas 77225, USA.
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40
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Knudsen GM, Nishida CR, Mooney SD, Ortiz de Montellano PR. Nitric-oxide synthase (NOS) reductase domain models suggest a new control element in endothelial NOS that attenuates calmodulin-dependent activity. J Biol Chem 2003; 278:31814-24. [PMID: 12805387 DOI: 10.1074/jbc.m303267200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Inducible (iNOS) and constitutive (eNOS, nNOS) nitric-oxide synthases differ in their Ca2+-calmodulin (CaM) dependence. iNOS binds CaM irreversibly but eNOS and nNOS, which bind CaM reversibly, have inserts in their reductase domains that regulate electron transfer. These include the 43-45-amino acid autoinhibitory element (AI) that attenuates electron transfer in the absence of CaM, and the C-terminal 20-40-amino acid tail that attenuates electron transfer in a CaM-independent manner. We constructed models of the reductase domains of the three NOS isoforms to predict the structural basis for CaM-dependent regulation. We have identified and characterized a loop (CD2A) within the NOS connecting domain that is highly conserved by isoform and that, like the AI element, is within direct interaction distance of the CaM binding region. The eNOS CD2A loop (eCD2A) has the sequence 834KGSPGGPPPG843, and is truncated to 809ESGSY813 (iCD2A) in iNOS. The eCD2A contributes to the Ca2+ dependence of CaM-bound activity to a level similar to that of the AI element. The eCD2A plays an autoinhibitory role in the control of NO, and CaM-dependent and -independent reductase activity, but this autoinhibitory function is masked by the dominant AI element. Finally, the iCD2A is involved in determining the salt dependence of NO activity at a post-flavin reduction level. Electrostatic interactions between the CD2A loop and the CaM-binding region, and CaM itself, provide a structural means for the CD2A to mediate CaM regulation of intra-subunit electron transfer within the active NOS complex.
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Affiliation(s)
- Giselle M Knudsen
- Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94143-2280, USA
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41
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Roman LJ, McLain J, Masters BSS. Chimeric enzymes of cytochrome P450 oxidoreductase and neuronal nitric-oxide synthase reductase domain reveal structural and functional differences. J Biol Chem 2003; 278:25700-7. [PMID: 12730215 DOI: 10.1074/jbc.m212309200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The nitric-oxide synthases (NOSs) are comprised of an oxygenase domain and a reductase domain bisected by a calmodulin (CaM) binding region. The NOS reductase domains share approximately 60% sequence similarity with the cytochrome P450 oxidoreductase (CYPOR), which transfers electrons to microsomal cytochromes P450. The crystal structure of the neuronal NOS (nNOS) connecting/FAD binding subdomains reveals that the structure of the nNOS-connecting subdomain diverges from that of CYPOR, implying different alignments of the flavins in the two enzymes. We created a series of chimeric enzymes between nNOS and CYPOR in which the FMN binding and the connecting/FAD binding subdomains are swapped. A chimera consisting of the nNOS heme domain and FMN binding subdomain and the CYPOR FAD binding subdomain catalyzed significantly increased rates of cytochrome c reduction in the absence of CaM and of NO synthesis in its presence. Cytochrome c reduction by this chimera was inhibited by CaM. Other chimeras consisting of the nNOS heme domain, the CYPOR FMN binding subdomain, and the nNOS FAD binding subdomain with or without the tail region also catalyzed cytochrome c reduction, were not modulated by CaM, and could not transfer electrons into the heme domain. A chimera consisting of the heme domain of nNOS and the reductase domain of CYPOR reduced cytochrome c and ferricyanide at rates 2-fold higher than that of native CYPOR, suggesting that the presence of the heme domain affected electron transfer through the reductase domain. These data demonstrate that the FMN subdomain of CYPOR cannot effectively substitute for that of nNOS, whereas the FAD subdomains are interchangeable. The differences among these chimeras most likely result from alterations in the alignment of the flavins within each enzyme construct.
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Affiliation(s)
- Linda J Roman
- Department of Biochemistry, The University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA.
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42
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Guan ZW, Iyanagi T. Electron transfer is activated by calmodulin in the flavin domain of human neuronal nitric oxide synthase. Arch Biochem Biophys 2003; 412:65-76. [PMID: 12646269 DOI: 10.1016/s0003-9861(03)00009-2] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The objective of this study was to clarify the mechanism of electron transfer in the human neuronal nitric oxide synthase (nNOS) flavin domain using the recombinant human nNOS flavin domains, the FAD/NADPH domain (contains FAD- and NADPH-binding sites), and the FAD/FMN domain (the flavin domain including a calmodulin-binding site). The reduction by NADPH of the two domains was studied by rapid-mixing, stopped-flow spectroscopy. For the FAD/NADPH domain, the results indicate that FAD is reduced by NADPH to generate the two-electron-reduced form (FADH(2)) and the reoxidation of the reduced FAD proceeds via a neutral (blue) semiquinone with molecular oxygen or ferricyanide, indicating that the reduced FAD is oxidized in two successive one-electron steps. The neutral (blue) semiquinone form, as an intermediate in the air-oxidation, was unstable in the presence of O(2). The purified FAD/NADPH domain prepared under our experimental conditions was activated by NADP(+) but not NAD(+). These results indicate that this domain exists in two states; an active state and a resting state, and the enzyme in the resting state can be activated by NADP(+). For the FAD/FMN domain, the reduction of the FAD-FMN pair of the oxidized enzyme with NADPH proceeded by both one-electron equivalent and two-electron equivalent mechanisms. The formation of semiquinones from the FAD-FMN pair was greatly increased in the presence of Ca(2+)/CaM. The air-stable semiquinone form, FAD-FMNH(.), was further rapidly reduced by NADPH with an increase at 520 nm, which is a characteristic peak of the FAD semiquinone. Results presented here indicate that intramolecular one-electron transfer from FAD to FMN is activated by the binding of Ca(2+)/CaM.
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Affiliation(s)
- Zhi-Wen Guan
- Department of Life Science, Faculty of Science, Himeji Institute of Technology, Harima Science Garden City, Hyogo 678-1279, Japan
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43
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Adak S, Sharma M, Meade AL, Stuehr DJ. A conserved flavin-shielding residue regulates NO synthase electron transfer and nicotinamide coenzyme specificity. Proc Natl Acad Sci U S A 2002; 99:13516-21. [PMID: 12359874 PMCID: PMC129705 DOI: 10.1073/pnas.192283399] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nitric oxide synthases (NOSs) are flavoheme enzymes that contain a ferredoxin:NADP(+)-reductase (FNR) module for binding NADPH and FAD and are unusual because their electron transfer reactions are controlled by the Ca(2+)-binding protein calmodulin. A conserved aromatic residue in the FNR module of NOS shields the isoalloxazine ring of FAD and is known to regulate NADPH binding affinity and specificity in related flavoproteins. We mutated Phe-1395 (F1395) in neuronal NOS to Tyr and Ser and tested their effects on nucleotide coenzyme specificity, catalytic activities, and electron transfer in the absence or presence of calmodulin. We found that the aromatic side chain of F1395 controls binding specificity with respect to NADH but does not greatly affect affinity for NADPH. Measures of flavin and heme reduction kinetics, ferricyanide and cytochrome c reduction, and NO synthesis established that the aromatic side chain of F1395 is required to repress electron transfer into and out of the flavins of neuronal NOS in the calmodulin-free state, and is also required for calmodulin to fully relieve this repression. We speculate that the phenyl side chain of F1395 is part of a conformational trigger mechanism that negatively or positively controls NOS electron transfer depending on the presence of calmodulin. Such use of the conserved aromatic residue broadens our understanding of flavoprotein structure and regulation.
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Affiliation(s)
- Subrata Adak
- Department of Immunology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
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44
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Craig DH, Chapman SK, Daff S. Calmodulin activates electron transfer through neuronal nitric-oxide synthase reductase domain by releasing an NADPH-dependent conformational lock. J Biol Chem 2002; 277:33987-94. [PMID: 12089147 DOI: 10.1074/jbc.m203118200] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Neuronal nitric-oxide synthase (nNOS) is activated by the Ca(2+)-dependent binding of calmodulin (CaM) to a characteristic polypeptide linker connecting the oxygenase and reductase domains. Calmodulin binding also activates the reductase domain of the enzyme, increasing the rate of reduction of external electron acceptors such as cytochrome c. Several unusual structural features appear to control this activation mechanism, including an autoinhibitory loop, a C-terminal extension, and kinase-dependent phosphorylation sites. Pre-steady state reduction and oxidation time courses for the nNOS reductase domain indicate that CaM binding triggers NADP(+) release, which may exert control over steady-state turnover. In addition, the second order rate constant for cytochrome c reduction in the absence of CaM was found to be highly dependent on the presence of NADPH. It appears that NADPH induces a conformational change in the nNOS reductase domain, restricting access to the FMN by external electron acceptors. CaM binding reverses this effect, causing a 30-fold increase in the second order rate constant. The results show a startling interplay between the two ligands, which both exert control over the conformation of the domain to influence its electron transfer properties. In the full-length enzyme, NADPH binding will probably close the conformational lock in vivo, preventing electron transfer to the oxygenase domain and the resultant stimulation of nitric oxide synthesis.
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Affiliation(s)
- Daniel H Craig
- Department of Chemistry, University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JJ, Scotland, United Kingdom
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45
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Nishida CR, Knudsen G, Straub W, Ortiz de Montellano PR. Electron supply and catalytic oxidation of nitrogen by cytochrome P450 and nitric oxide synthase. Drug Metab Rev 2002; 34:479-501. [PMID: 12214661 DOI: 10.1081/dmr-120005648] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Cytochrome P450 and nitric oxide synthase (NOS) oxidize nitrogen atoms, although the substrates and transformations are highly restricted for NOS. The first reaction catalyzed by NOS is mediated by a P450-like ferryl species, although it is generated by a distinct process in which a tetrahydrobiopterin molecule in NOS serves as a transient electron donor. The second NOS reaction appears to be mediated by an iron dioxygen precursor of the ferryl species. The transient tetrahydrobiopterin radical formed in these reactions is quenched by electron transfer from the NOS flavin domain. Electron transfer from the flavins is controlled by the binding of calmodulin, the presence of peptide inserts in the flavin domain, the substrate structure, and phosphorylation of the enzyme.
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Affiliation(s)
- Clinton R Nishida
- Department of Pharmaceutical Chemistry, University of California, San Francisco 94143-0446, USA
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46
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Lane P, Gross SS. Disabling a C-terminal autoinhibitory control element in endothelial nitric-oxide synthase by phosphorylation provides a molecular explanation for activation of vascular NO synthesis by diverse physiological stimuli. J Biol Chem 2002; 277:19087-94. [PMID: 11839759 DOI: 10.1074/jbc.m200258200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Calmodulin-dependent activation of endothelial nitric-oxide synthase is generally considered to follow a transient increase in intracellular calcium levels. However, a number of physiological stimuli (e.g. endothelial shear-stress, insulin) are known to activate endothelial nitric oxide (eNOS) via a non-classical, "calcium-independent" pathway. Recent findings demonstrate that such stimuli elicit the phosphorylation of a C-terminal residue in eNOS (Ser(1179) in the bovine isoform), rendering eNOS active at resting levels of intracellular calcium. However, the mechanistic basis for this mode of eNOS activation remains unknown. Protein modeling led us to consider that the C terminus of eNOS may fulfill an autoinhibitory function that can be disrupted by phosphorylation of serine 1179. To test this possibility we contrasted the phenotype of wild type bovine eNOS with that of a mutant lacking C-terminal residues 1179-1205 (CDelta27 eNOS). Despite no observed difference in calmodulin affinity, CDelta27 eNOS exhibited a 5-fold reduction in EC(50) for calcium and a 2-4-fold increase in maximal catalytic activities. In these phenotypic properties, CDelta27 accurately mimics phospho-Ser(1179) wild type eNOS. We conclude that the C terminus imposes a significant barrier to the activation of eNOS by calmodulin binding and that this barrier can be functionally disabled by Ser(1179) phosphorylation-elicited enzyme activation.
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Affiliation(s)
- Paul Lane
- Department of Pharmacology and the Program in Biochemistry and Structural Biology, Weill Medical College of Cornell University, New York, New York 10021, USA
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Rozhkova EA, Fujimoto N, Sagami I, Daff SN, Shimizu T. Interactions between the isolated oxygenase and reductase domains of neuronal nitric-oxide synthase: assessing the role of calmodulin. J Biol Chem 2002; 277:16888-94. [PMID: 11884406 DOI: 10.1074/jbc.m200642200] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nitric-oxide synthase (NOS) is a fusion protein composed of an oxygenase domain with a heme-active site and a reductase domain with an NADPH binding site and requires Ca(2+)/calmodulin (CaM) for NO formation activity. We studied NO formation activity in reconstituted systems consisting of the isolated oxygenase and reductase domains of neuronal NOS with and without the CaM binding site. Reductase domains with 33-amino acid C-terminal truncations were also examined. These were shown to have faster cytochrome c reduction rates in the absence of CaM. N(G)-hydroxy-l-Arg, an intermediate in the physiological NO synthesis reaction, was found to be a viable substrate. Turnover rates for N(G)-hydroxy-l-Arg in the absence of Ca(2+)/CaM in most of the reconstituted systems were 2.3-3.1 min(-1). Surprisingly, the NO formation activities with CaM binding sites on either reductase or oxygenase domains were decreased dramatically on addition of Ca(2+)/CaM. However, NADPH oxidation and cytochrome c reduction rates were increased by the same procedure. Activation of the reductase domains by CaM addition or by C-terminal deletion failed to increase the rate of NO synthesis. Therefore, both mechanisms appear to be less important than the domain-domain interaction, which is controlled by CaM binding in wild-type neuronal NOS, but not in the reconstituted systems.
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Affiliation(s)
- Elena A Rozhkova
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan
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Roman LJ, Martásek P, Masters BSS. Intrinsic and extrinsic modulation of nitric oxide synthase activity. Chem Rev 2002; 102:1179-90. [PMID: 11942792 DOI: 10.1021/cr000661e] [Citation(s) in RCA: 163] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Linda J Roman
- Department of Biochemistry, The University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
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Affiliation(s)
- Gerald M Rosen
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, MD 21201, USA
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Sagami I, Sato Y, Noguchi T, Miyajima M, Rozhkova E, Daff S, Shimizu T. Electron transfer in nitric-oxide synthase. Coord Chem Rev 2002. [DOI: 10.1016/s0010-8545(01)00446-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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