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Douglass MS, Kaplowitz MR, Zhang Y, Fike CD. Impact of l-citrulline on nitric oxide signaling and arginase activity in hypoxic human pulmonary artery endothelial cells. Pulm Circ 2023; 13:e12221. [PMID: 37063746 PMCID: PMC10091859 DOI: 10.1002/pul2.12221] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Revised: 03/28/2023] [Accepted: 03/30/2023] [Indexed: 04/18/2023] Open
Abstract
Impaired nitric oxide (NO) signaling contributes to the development of pulmonary hypertension (PH). The l-arginine precursor, l-citrulline, improves NO signaling and has therapeutic potential in PH. However, there is evidence that l-citrulline might increase arginase activity, which in turn, has been shown to contribute to PH. Our major purpose was to determine if l-citrulline increases arginase activity in hypoxic human pulmonary artery endothelial cells (PAECs). In addition, to avoid potential adverse effects from high dose l-citrulline monotherapy, we evaluated whether the effect on NO signaling is greater using co-treatment with l-citrulline and another agent that improves NO signaling, folic acid, than either alone. Arginase activity was measured in human PAECs cultured under hypoxic conditions in the presence of l-citrulline (0-1 mM). NO production and endothelial nitric oxide synthase (eNOS) coupling, as assessed by eNOS dimer-to-monomer ratios, were measured in PAECs treated with l-citrulline and/or folic acid (0.2 μM). Arginase activity increased in hypoxic PAECs treated with 1 mM but not with either 0.05 or 0.1 mM l-citrulline. Co-treatment with folic acid and 0.1 mM l-citrulline increased NO production and eNOS dimer-to-monomer ratios more than treatment with either alone. The potential to increase arginase activity suggests that there might be plasma l-citrulline concentrations that should not be exceeded when using l-citrulline to treat PH. Rather than progressively increasing the dose of l-citrulline as a monotherapy, co-therapy with l-citrulline and folic acid merits consideration, due to the possibility of achieving efficacy at lower doses and minimizing side effects.
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Affiliation(s)
| | | | - Yongmei Zhang
- Department of PediatricsUniversity of UtahSalt Lake CityUtahUSA
| | - Candice D. Fike
- Department of PediatricsUniversity of UtahSalt Lake CityUtahUSA
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2
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Douglass M, Dikalova A, Kaplowitz MR, Zhang Y, Cunningham G, Summar M, Fike CD. Folic acid, either solely or combined with L-citrulline, improves NO signaling and ameliorates chronic hypoxia-induced pulmonary hypertension in newborn pigs. Physiol Rep 2021; 9:e15096. [PMID: 34762361 PMCID: PMC8582293 DOI: 10.14814/phy2.15096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Revised: 09/29/2021] [Accepted: 10/02/2021] [Indexed: 11/24/2022] Open
Abstract
Concomitant with developing pulmonary hypertension (PH), newborn piglets exposed to chronic hypoxia develop pulmonary vascular NO signaling impairments. PH is reduced and NO signaling is improved in chronically hypoxic piglets treated with the NO-arginine precursor, L-citrulline. Folic acid positively impacts NO signaling. We evaluated whether the effect on NO signaling and PH is greater using co-treatment with folic acid and L-citrulline than either alone. From day 3 to day 10 of hypoxia, piglets were treated solely with folic acid, solely with L-citrulline, or co-treated with both. Catheters were placed to measure in vivo hemodynamics. NO production was measured in vitro in dissected pulmonary arteries. Compared to normoxic piglets, pulmonary vascular resistance (PVR) was elevated and NO production was reduced in untreated hypoxic piglets. Regardless of treatment strategy, PVR was less in all three treated groups of hypoxic piglets when compared to the untreated hypoxic group. In addition, for all three groups of treated hypoxic piglets, NO production was higher than the untreated group. Improvements in PVR and NO production did not differ between piglets co-treated with folic acid and L-citrulline and those treated solely with either. Thus, the impact on NO production and PVR was not augmented by combining folic acid and L-citrulline treatments. Nonetheless, treatment with folic acid, either singly or when combined with L-citrulline, increases NO production and inhibits PH in chronically hypoxic newborn piglets. Folic acid merits consideration as a therapy for PH in human infants with chronic heart and lung conditions that are associated with chronic hypoxia.
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Affiliation(s)
- Matthew Douglass
- Department of PediatricsUniversity of Utah HealthSalt Lake CityUtahUSA
| | - Anna Dikalova
- Department of MedicineVanderbilt University Medical CenterNashvilleTennesseeUSA
| | - Mark R. Kaplowitz
- Department of PediatricsUniversity of Utah HealthSalt Lake CityUtahUSA
| | - Yongmei Zhang
- Department of PediatricsUniversity of Utah HealthSalt Lake CityUtahUSA
| | - Gary Cunningham
- Division of Genetics and MetabolismChildren’s National Medical CenterWashingtonDistrict of ColumbiaUSA
| | - Marshall Summar
- Division of Genetics and MetabolismChildren’s National Medical CenterWashingtonDistrict of ColumbiaUSA
| | - Candice D. Fike
- Department of PediatricsUniversity of Utah HealthSalt Lake CityUtahUSA
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Martínez-Banaclocha M. N-acetyl-cysteine in Schizophrenia: Potential Role on the Sensitive Cysteine Proteome. Curr Med Chem 2021; 27:6424-6439. [PMID: 33115390 DOI: 10.2174/0929867326666191015091346] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2019] [Revised: 09/11/2019] [Accepted: 10/02/2019] [Indexed: 12/14/2022]
Abstract
BACKGROUND N-acetyl-cysteine (NAC) has shown widespread utility in different psychiatric disorders, including a beneficial role in schizophrenic patients. Although the replenishment of glutathione and the antioxidant activity of NAC have been suggested as the mechanisms that improve such a wide range of disorders, none seems to be sufficiently specific to explain these intriguing effects. A sensitive cysteine proteome is emerging as a functional and structural network of interconnected Sensitive Cysteine-containing Proteins (SCCPs) that together with reactive species and the cysteine/ glutathione cycles can regulate the bioenergetic metabolism, the redox homeostasis and the cellular growth, differentiation and survival, acting through different pathways that are regulated by the same thiol radical in cysteine residues. OBJECTIVE Since this sensitive cysteine network has been implicated in the pathogenesis of Parkinson's and Alzheimer's diseases, I have reviewed if the proteins that play a role in schizophrenia can be classified as SCCPs. RESULTS The results show that the principal proteins playing a role in schizophrenia can be classified as SCCPs, suggesting that the sensitive cysteine proteome (cysteinet) is defective in this type of psychosis. CONCLUSION The present review proposes that there is a deregulation of the sensitive cysteine proteome in schizophrenia as the consequence of a functional imbalance among different SCCPs, which play different functions in neurons and glial cells. In this context, the role of NAC to restore and prevent schizophrenic disorders is discussed.
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Oxidative Stress Orchestrates MAPK and Nitric-Oxide Synthase Signal. Int J Mol Sci 2020; 21:ijms21228750. [PMID: 33228180 PMCID: PMC7699490 DOI: 10.3390/ijms21228750] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Revised: 11/17/2020] [Accepted: 11/17/2020] [Indexed: 12/15/2022] Open
Abstract
Reactive oxygen species (ROS) are not only harmful to cell survival but also essential to cell signaling through cysteine-based redox switches. In fact, ROS triggers the potential activation of mitogen-activated protein kinases (MAPKs). The 90 kDa ribosomal S6 kinase 1 (RSK1), one of the downstream mediators of the MAPK pathway, is implicated in various cellular processes through phosphorylating different substrates. As such, RSK1 associates with and phosphorylates neuronal nitric oxide (NO) synthase (nNOS) at Ser847, leading to a decrease in NO generation. In addition, the RSK1 activity is sensitive to inhibition by reversible cysteine-based redox modification of its Cys223 during oxidative stress. Aside from oxidative stress, nitrosative stress also contributes to cysteine-based redox modification. Thus, the protein kinases such as Ca2+/calmodulin (CaM)-dependent protein kinase I (CaMKI) and II (CaMKII) that phosphorylate nNOS could be potentially regulated by cysteine-based redox modification. In this review, we focus on the role of post-translational modifications in regulating nNOS and nNOS-phosphorylating protein kinases and communication among themselves.
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Dikalova A, Aschner JL, Kaplowitz MR, Cunningham G, Summar M, Fike CD. Combined l-citrulline and tetrahydrobiopterin therapy improves NO signaling and ameliorates chronic hypoxia-induced pulmonary hypertension in newborn pigs. Am J Physiol Lung Cell Mol Physiol 2020; 318:L762-L772. [PMID: 32073878 PMCID: PMC7191483 DOI: 10.1152/ajplung.00280.2019] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Revised: 02/05/2020] [Accepted: 02/12/2020] [Indexed: 01/21/2023] Open
Abstract
Newborn pigs with chronic hypoxia-induced pulmonary hypertension (PH) have evidence of endothelial nitric oxide synthase (eNOS) uncoupling. In this model, we showed that therapies that promote eNOS coupling, either tetrahydrobiopterin (BH4), a NOS cofactor, or l-citrulline, a NO-l-arginine precursor, inhibit PH. We wanted to determine whether cotreatment with l-citrulline and a BH4 compound, sapropterin dihydrochloride, improves NO signaling and chronic hypoxia-induced PH more markedly than either alone. Normoxic (control) and hypoxic piglets were studied. Some hypoxic piglets received sole treatment with l-citrulline or BH4, or were cotreated with l-citrulline and BH4, from day 3 through day 10 of hypoxia. Catheters were placed for hemodynamic measurements, and pulmonary arteries were dissected to assess eNOS dimer-to-monomer ratios and NO production. In untreated hypoxic piglets, pulmonary vascular resistance (PVR) was higher and NO production and eNOS dimer-to-monomer ratios were lower than in normoxic piglets. Compared with the untreated hypoxic group, PVR was lower in hypoxic piglets cotreated with l-citrulline and BH4 and in those treated with l-citrulline alone but not for those treated solely with BH4. NO production and eNOS dimer-to-monomer ratios were greater for all three treated hypoxic groups compared with the untreated group. Notably, greater improvements in PVR, eNOS dimer-to-monomer ratios, and NO production were found in hypoxic piglets cotreated with l-citrulline and BH4 than in piglets treated with either alone. Cotreatment with l-citrulline and BH4 more effectively improves NO signaling and inhibits chronic hypoxia-induced PH than either treatment alone. Combination therapies may offer enhanced therapeutic capacity for challenging clinical conditions, such as chronic neonatal PH.
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Affiliation(s)
- Anna Dikalova
- Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Judy L Aschner
- Department of Pediatrics, Albert Einstein College of Medicine, New York, New York
- Department of Pediatrics, Hackensack Meridian Health School of Medicine at Seton Hall University, Nutley, New Jersey
| | - Mark R Kaplowitz
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, Tennessee
- Department of Pediatrics, University of Utah Health, Salt Lake City, Utah
| | - Gary Cunningham
- Division of Genetics and Metabolism, Children's National Medical Center, Washington, District of Columbia
| | - Marshall Summar
- Division of Genetics and Metabolism, Children's National Medical Center, Washington, District of Columbia
| | - Candice D Fike
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, Tennessee
- Department of Pediatrics, University of Utah Health, Salt Lake City, Utah
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6
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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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7
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Fike CD, Dikalova A, Kaplowitz MR, Cunningham G, Summar M, Aschner JL. Rescue Treatment with L-Citrulline Inhibits Hypoxia-Induced Pulmonary Hypertension in Newborn Pigs. Am J Respir Cell Mol Biol 2015; 53:255-64. [PMID: 25536367 DOI: 10.1165/rcmb.2014-0351oc] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Infants with cardiopulmonary disorders associated with hypoxia develop pulmonary hypertension. We previously showed that initiation of oral L-citrulline before and continued throughout hypoxic exposure improves nitric oxide (NO) production and ameliorates pulmonary hypertension in newborn piglets. Rescue treatments, initiated after the onset of pulmonary hypertension, better approximate clinical strategies. Mechanisms by which L-citrulline improves NO production merit elucidation. The objective of this study was to determine whether starting L-citrulline after the onset of pulmonary hypertension inhibits disease progression and improves NO production by recoupling endothelial NO synthase (eNOS). Hypoxic and normoxic (control) piglets were studied. Some hypoxic piglets received oral L-citrulline starting on Day 3 of hypoxia and continuing throughout the remaining 7 days of hypoxic exposure. Catheters were placed for hemodynamic measurements, and pulmonary arteries were dissected to assess NO production and eNOS dimer-to-monomer ratios (a measure of eNOS coupling). Pulmonary vascular resistance was lower in L-citrulline-treated hypoxic piglets than in untreated hypoxic piglets but was higher than in normoxic controls. NO production and eNOS dimer-to-monomer ratios were greater in pulmonary arteries from L-citrulline-treated than from untreated hypoxic animals but were lower than in normoxic controls. When started after disease onset, oral L-citrulline treatment improves NO production by recoupling eNOS and inhibits the further development of chronic hypoxia-induced pulmonary hypertension in newborn piglets. Oral L-citrulline may be a novel strategy to halt or reverse pulmonary hypertension in infants suffering from cardiopulmonary conditions associated with hypoxia.
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Affiliation(s)
- Candice D Fike
- 1 Department of Pediatrics, Vanderbilt University Medical Center, Nashville, Tennessee.,2 Monroe Carell Jr. Children's Hospital at Vanderbilt, Nashville, Tennessee
| | - Anna Dikalova
- 1 Department of Pediatrics, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Mark R Kaplowitz
- 1 Department of Pediatrics, Vanderbilt University Medical Center, Nashville, Tennessee
| | - Gary Cunningham
- 3 Division of Genetics and Metabolism, Children's National Medical Center, Washington, District of Columbia; and
| | - Marshall Summar
- 3 Division of Genetics and Metabolism, Children's National Medical Center, Washington, District of Columbia; and
| | - Judy L Aschner
- 4 Department of Pediatrics, Albert Einstein College of Medicine and the Children's Hospital at Montefiore, New York, New York
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8
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Konradi J, Mollenhauer M, Baldus S, Klinke A. Redox-sensitive mechanisms underlying vascular dysfunction in heart failure. Free Radic Res 2015; 49:721-42. [DOI: 10.3109/10715762.2015.1027200] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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9
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Molecular modeling and simulation of the human eNOS reductase domain, an enzyme involved in the release of vascular nitric oxide. J Mol Model 2014; 20:2470. [DOI: 10.1007/s00894-014-2470-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2014] [Accepted: 09/14/2014] [Indexed: 01/19/2023]
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10
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Chreifi G, Li H, McInnes C, Gibson CL, Suckling CJ, Poulos TL. Communication between the zinc and tetrahydrobiopterin binding sites in nitric oxide synthase. Biochemistry 2014; 53:4216-23. [PMID: 24819538 PMCID: PMC4082377 DOI: 10.1021/bi5003986] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2014] [Revised: 05/10/2014] [Indexed: 01/02/2023]
Abstract
The nitric oxide synthase (NOS) dimer is stabilized by a Zn(2+) ion coordinated to four symmetry-related Cys residues exactly along the dimer 2-fold axis. Each of the two essential tetrahydrobiopterin (H4B) molecules in the dimer interacts directly with the heme, and each H4B molecule is ~15 Å from the Zn(2+). We have determined the crystal structures of the bovine endothelial NOS dimer oxygenase domain bound to three different pterin analogues, which reveal an intimate structural communication between the H4B and Zn(2+) sites. The binding of one of these compounds, 6-acetyl-2-amino-7,7-dimethyl-7,8-dihydro-4(3H)-pteridinone (1), to the pterin site and Zn(2+) binding are mutually exclusive. Compound 1 both directly and indirectly disrupts hydrogen bonding between key residues in the Zn(2+) binding motif, resulting in destabilization of the dimer and a complete disruption of the Zn(2+) site. Addition of excess Zn(2+) stabilizes the Zn(2+) site at the expense of weakened binding of 1. The unique structural features of 1 that disrupt the dimer interface are extra methyl groups that extend into the dimer interface and force a slight opening of the dimer, thus resulting in disruption of the Zn(2+) site. These results illustrate a very delicate balance of forces and structure at the dimer interface that must be maintained to properly form the Zn(2+), pterin, and substrate binding sites.
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Affiliation(s)
- Georges Chreifi
- Departments of Molecular Biology and Biochemistry, Chemistry, and Pharmaceutical
Sciences, University of California, Irvine, California 92697-3900, United States
| | - Huiying Li
- Departments of Molecular Biology and Biochemistry, Chemistry, and Pharmaceutical
Sciences, University of California, Irvine, California 92697-3900, United States
| | - Craig
R. McInnes
- WestCHEM,
Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, Scotland, U.K.
| | - Colin L. Gibson
- WestCHEM,
Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, Scotland, U.K.
| | - Colin J. Suckling
- WestCHEM,
Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, Scotland, U.K.
| | - Thomas L. Poulos
- Departments of Molecular Biology and Biochemistry, Chemistry, and Pharmaceutical
Sciences, University of California, Irvine, California 92697-3900, United States
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11
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Bendall JK, Douglas G, McNeill E, Channon KM, Crabtree MJ. Tetrahydrobiopterin in cardiovascular health and disease. Antioxid Redox Signal 2014; 20:3040-77. [PMID: 24294830 PMCID: PMC4038990 DOI: 10.1089/ars.2013.5566] [Citation(s) in RCA: 164] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Revised: 11/01/2013] [Accepted: 12/02/2013] [Indexed: 01/03/2023]
Abstract
Tetrahydrobiopterin (BH4) functions as a cofactor for several important enzyme systems, and considerable evidence implicates BH4 as a key regulator of endothelial nitric oxide synthase (eNOS) in the setting of cardiovascular health and disease. BH4 bioavailability is determined by a balance of enzymatic de novo synthesis and recycling, versus degradation in the setting of oxidative stress. Augmenting vascular BH4 levels by pharmacological supplementation has been shown in experimental studies to enhance NO bioavailability. However, it has become more apparent that the role of BH4 in other enzymatic pathways, including other NOS isoforms and the aromatic amino acid hydroxylases, may have a bearing on important aspects of vascular homeostasis, inflammation, and cardiac function. This article reviews the role of BH4 in cardiovascular development and homeostasis, as well as in pathophysiological processes such as endothelial and vascular dysfunction, atherosclerosis, inflammation, and cardiac hypertrophy. We discuss the therapeutic potential of BH4 in cardiovascular disease states and attempt to address how this modulator of intracellular NO-redox balance may ultimately provide a powerful new treatment for many cardiovascular diseases.
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Affiliation(s)
- Jennifer K Bendall
- Division of Cardiovascular Medicine, British Heart Foundation Centre of Research Excellence, University of Oxford , John Radcliffe Hospital, Oxford, United Kingdom
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12
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Sodium-coupled neutral amino acid transporter 1 (SNAT1) modulates L-citrulline transport and nitric oxide (NO) signaling in piglet pulmonary arterial endothelial cells. PLoS One 2014; 9:e85730. [PMID: 24454923 PMCID: PMC3893279 DOI: 10.1371/journal.pone.0085730] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 11/30/2013] [Indexed: 01/22/2023] Open
Abstract
RATIONALE There is evidence that impairments in nitric oxide (NO) signaling contribute to chronic hypoxia-induced pulmonary hypertension. The L-arginine-NO precursor, L-citrulline, has been shown to ameliorate pulmonary hypertension. Sodium-coupled neutral amino acid transporters (SNATs) are involved in the transport of L-citrulline into pulmonary arterial endothelial cells (PAECs). The functional link between the SNATs, L-citrulline, and NO signaling has not yet been explored. OBJECTIVE We tested the hypothesis that changes in SNAT1 expression and transport function regulate NO production by modulating eNOS coupling in newborn piglet PAECs. METHODS AND RESULTS A silencing RNA (siRNA) technique was used to assess the contribution of SNAT1 to NO production and eNOS coupling (eNOS dimer-to-monomer ratios) in PAECs from newborn piglets cultured under normoxic and hypoxic conditions in the presence and absence of L-citrulline. SNAT1 siRNA reduced basal NO production in normoxic PAECs and prevented L-citrulline-induced elevations in NO production in both normoxic and hypoxic PAECs. SNAT1 siRNA reduced basal eNOS dimer-to-monomer ratios in normoxic PAECs and prevented L-citrulline-induced increases in eNOS dimer-to-monomer ratios in hypoxic PAECs. CONCLUSIONS SNAT1 mediated L-citrulline transport modulates eNOS coupling and thus regulates NO production in hypoxic PAECs from newborn piglets. Strategies that increase SNAT1-mediated transport and supply of L-citrulline may serve as novel therapeutic approaches to enhance NO production in patients with pulmonary vascular disease.
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13
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N-methyl-D-aspartate receptor-dependent denitrosylation of neuronal nitric oxide synthase increase the enzyme activity. PLoS One 2012; 7:e52788. [PMID: 23285183 PMCID: PMC3532120 DOI: 10.1371/journal.pone.0052788] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2012] [Accepted: 11/21/2012] [Indexed: 11/19/2022] Open
Abstract
Our laboratory once reported that neuronal nitric oxide synthase (nNOS) S-nitrosylation was decreased in rat hippocampus during cerebral ischemia-reperfusion, but the underlying mechanism was unclear. In this study, we show that nNOS activity is dynamically regulated by S-nitrosylation. We found that overexpressed nNOS in HEK293 (human embryonic kidney) cells could be S-nitrosylated by exogenous NO donor GSNO and which is associated with the enzyme activity decrease. Cys331, one of the zinc-tetrathiolate cysteines, was identified as the key site of nNOS S-nitrosylation. In addition, we also found that nNOS is highly S-nitrosylated in resting rat hippocampal neurons and the enzyme undergos denitrosylation during the process of rat brain ischemia/reperfusion. Intrestingly, the process of nNOS denitrosylation is coupling with the decrease of nNOS phosphorylation at Ser847, a site associated with nNOS activation. Further more, we document that nNOS denitrosylation could be suppressed by pretreatment of neurons with MK801, an antagonist of NMDAR, GSNO, EGTA, BAPTA, W-7, an inhibitor of calmodulin as well as TrxR1 antisense oligonucleotide (AS-ODN) respectively. Taken together, our data demonstrate that the denitrosylation of nNOS induced by calcium ion influx is a NMDAR-dependent process during the early stage of ischemia/reperfusion, which is majorly mediated by thioredoxin-1 (Trx1) system. nNOS dephosphorylation may be induced by the enzyme denitrosylation, which suggest that S-nitrosylation/denitrosylation of nNOS may be an important mechanism in regulating the enzyme activity.
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14
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Förstermann U, Sessa WC. Nitric oxide synthases: regulation and function. Eur Heart J 2012; 33:829-37, 837a-837d. [PMID: 21890489 PMCID: PMC3345541 DOI: 10.1093/eurheartj/ehr304] [Citation(s) in RCA: 2610] [Impact Index Per Article: 217.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2011] [Revised: 07/14/2011] [Accepted: 07/28/2011] [Indexed: 02/06/2023] Open
Abstract
Nitric oxide (NO), the smallest signalling molecule known, is produced by three isoforms of NO synthase (NOS; EC 1.14.13.39). They all utilize l-arginine and molecular oxygen as substrates and require the cofactors reduced nicotinamide-adenine-dinucleotide phosphate (NADPH), flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN), and (6R-)5,6,7,8-tetrahydrobiopterin (BH(4)). All NOS bind calmodulin and contain haem. Neuronal NOS (nNOS, NOS I) is constitutively expressed in central and peripheral neurons and some other cell types. Its functions include synaptic plasticity in the central nervous system (CNS), central regulation of blood pressure, smooth muscle relaxation, and vasodilatation via peripheral nitrergic nerves. Nitrergic nerves are of particular importance in the relaxation of corpus cavernosum and penile erection. Phosphodiesterase 5 inhibitors (sildenafil, vardenafil, and tadalafil) require at least a residual nNOS activity for their action. Inducible NOS (NOS II) can be expressed in many cell types in response to lipopolysaccharide, cytokines, or other agents. Inducible NOS generates large amounts of NO that have cytostatic effects on parasitic target cells. Inducible NOS contributes to the pathophysiology of inflammatory diseases and septic shock. Endothelial NOS (eNOS, NOS III) is mostly expressed in endothelial cells. It keeps blood vessels dilated, controls blood pressure, and has numerous other vasoprotective and anti-atherosclerotic effects. Many cardiovascular risk factors lead to oxidative stress, eNOS uncoupling, and endothelial dysfunction in the vasculature. Pharmacologically, vascular oxidative stress can be reduced and eNOS functionality restored with renin- and angiotensin-converting enzyme-inhibitors, with angiotensin receptor blockers, and with statins.
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Affiliation(s)
- Ulrich Förstermann
- Department of Pharmacology, Johannes Gutenberg University Medical Center, 55101 Mainz, Germany.
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15
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Clapp KM, Peng HM, Morishima Y, Lau M, Walker VJ, Pratt WB, Osawa Y. C331A mutant of neuronal nitric-oxide synthase is labilized for Hsp70/CHIP (C terminus of HSC70-interacting protein)-dependent ubiquitination. J Biol Chem 2010; 285:33642-51. [PMID: 20729196 DOI: 10.1074/jbc.m110.159178] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
It is established that suicide inactivation of neuronal nitric-oxide synthase (nNOS) by drugs and other xenobiotics leads to ubiquitination and proteasomal degradation of the enzyme. The exact mechanism is not known, although it is widely thought that the covalent alteration of the active site during inactivation triggers the degradation. A mechanism that involves recognition of the altered nNOS by Hsp70 and its cochaperone CHIP, an E3-ubiquitin ligase, has been proposed. To further address how alterations of the active site trigger ubiquitination of nNOS, we examined a C331A nNOS mutant, which was reported to have impaired ability to bind L-arginine and tetrahydrobiopterin. We show here that C331A nNOS is highly susceptible to ubiquitination by a purified system containing ubiquitinating enzymes and chaperones, by the endogenous ubiquitinating system in reticulocyte lysate fraction II, and by intact HEK293 cells. The involvement of the altered heme cleft in regulating ubiquitination is confirmed by the finding that the slowly reversible inhibitor of nNOS, N(G)-nitro-L-arginine, but not its inactive D-isomer, protects the C331A nNOS from ubiquitination in all these experimental systems. We also show that both Hsp70 and CHIP play a major role in the ubiquitination of C331A nNOS, although Hsp90 protects from ubiquitination. Thus, these studies further strengthen the link between the mobility of the substrate-binding cleft and chaperone-dependent ubiquitination of nNOS. These results support a general model of chaperone-mediated protein quality control and lead to a novel mechanism for substrate stabilization based on nNOS interaction with the chaperone machinery.
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Affiliation(s)
- Kelly M Clapp
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA
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16
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Förstermann U. Nitric oxide and oxidative stress in vascular disease. Pflugers Arch 2010; 459:923-39. [PMID: 20306272 DOI: 10.1007/s00424-010-0808-2] [Citation(s) in RCA: 493] [Impact Index Per Article: 35.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2010] [Accepted: 02/16/2010] [Indexed: 02/07/2023]
Abstract
Endothelium-derived nitric oxide (NO) is a paracrine factor that controls vascular tone, inhibits platelet function, prevents adhesion of leukocytes, and reduces proliferation of the intima. An enhanced inactivation and/or reduced synthesis of NO is seen in conjunction with risk factors for cardiovascular disease. This condition, referred to as endothelial dysfunction, can promote vasospasm, thrombosis, vascular inflammation, and proliferation of vascular smooth muscle cells. Vascular oxidative stress with an increased production of reactive oxygen species (ROS) contributes to mechanisms of vascular dysfunction. Oxidative stress is mainly caused by an imbalance between the activity of endogenous pro-oxidative enzymes (such as NADPH oxidase, xanthine oxidase, or the mitochondrial respiratory chain) and anti-oxidative enzymes (such as superoxide dismutase, glutathione peroxidase, heme oxygenase, thioredoxin peroxidase/peroxiredoxin, catalase, and paraoxonase) in favor of the former. Also, small molecular weight antioxidants may play a role in the defense against oxidative stress. Increased ROS concentrations reduce the amount of bioactive NO by chemical inactivation to form toxic peroxynitrite. Peroxynitrite-in turn-can "uncouple" endothelial NO synthase to become a dysfunctional superoxide-generating enzyme that contributes to vascular oxidative stress. Oxidative stress and endothelial dysfunction can promote atherogenesis. Therapeutically, drugs in clinical use such as ACE inhibitors, AT(1) receptor blockers, and statins have pleiotropic actions that can improve endothelial function. Also, dietary polyphenolic antioxidants can reduce oxidative stress, whereas clinical trials with antioxidant vitamins C and E failed to show an improved cardiovascular outcome.
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Affiliation(s)
- Ulrich Förstermann
- Department of Pharmacology, Johannes Gutenberg University Medical Center, Obere Zahlbacher Strasse 67, 55101, Mainz, Germany.
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Chen W, Druhan LJ, Chen CA, Hemann C, Chen YR, Berka V, Tsai AL, Zweier JL. Peroxynitrite induces destruction of the tetrahydrobiopterin and heme in endothelial nitric oxide synthase: transition from reversible to irreversible enzyme inhibition. Biochemistry 2010; 49:3129-37. [PMID: 20184376 PMCID: PMC2851177 DOI: 10.1021/bi9016632] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Endothelial nitric oxide synthase (eNOS) is an important regulator of vascular and cardiac function. Peroxynitrite (ONOO(-)) inactivates eNOS, but questions remain regarding the mechanisms of this process. It has been reported that inactivation is due to oxidation of the eNOS zinc-thiolate cluster, rather than the cofactor tetrahydrobiopterin (BH(4)); however, this remains highly controversial. Therefore, we investigated the mechanisms of ONOO(-)-induced eNOS dysfunction and their dose dependence. Exposure of human eNOS to ONOO(-) resulted in a dose-dependent loss of activity with a marked destabilization of the eNOS dimer. HPLC analysis indicated that both free and eNOS-bound BH(4) were oxidized during exposure to ONOO(-); however, full oxidation of protein-bound biopterin required higher ONOO(-) levels. Additionally, ONOO(-) triggered changes in the UV/visible spectrum and heme content of the enzyme. Preincubation of eNOS with BH(4) decreased dimer destabilization and heme alteration. Addition of BH(4) to the ONOO(-)-destabilized eNOS dimer only partially rescued enzyme function. In contrast to ONOO(-) treatment, incubation with the zinc chelator TPEN with removal of enzyme-bound zinc did not change the eNOS activity or stability of the SDS-resistant eNOS dimer, demonstrating that the dimer stabilization induced by BH(4) does not require zinc occupancy of the zinc-thiolate cluster. While ONOO(-) treatment was observed to induce loss of Zn binding, this cannot account for the loss of enzyme activity. Therefore, ONOO(-)-induced eNOS inactivation is primarily due to oxidation of BH(4) and irreversible destruction of the heme/heme center.
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Affiliation(s)
- Weiguo Chen
- Davis Heart & Lung Research Institute, Division of Cardiovascular Medicine, Department of Internal Medicine, College of Medicine, The Ohio State University, Columbus, Ohio 43210
| | - Lawrence J. Druhan
- Davis Heart & Lung Research Institute, Division of Cardiovascular Medicine, Department of Internal Medicine, College of Medicine, The Ohio State University, Columbus, Ohio 43210
| | - Chun-An Chen
- Davis Heart & Lung Research Institute, Division of Cardiovascular Medicine, Department of Internal Medicine, College of Medicine, The Ohio State University, Columbus, Ohio 43210
| | - Craig Hemann
- Davis Heart & Lung Research Institute, Division of Cardiovascular Medicine, Department of Internal Medicine, College of Medicine, The Ohio State University, Columbus, Ohio 43210
| | - Yeong-Renn Chen
- Davis Heart & Lung Research Institute, Division of Cardiovascular Medicine, Department of Internal Medicine, College of Medicine, The Ohio State University, Columbus, Ohio 43210
| | - Vladimir Berka
- Division of Hematology, Department of Internal Medicine, University of Texas Health Science Center at Houston, Houston, Texas 77030
| | - Ah-Lim Tsai
- Division of Hematology, Department of Internal Medicine, University of Texas Health Science Center at Houston, Houston, Texas 77030
| | - Jay L. Zweier
- Davis Heart & Lung Research Institute, Division of Cardiovascular Medicine, Department of Internal Medicine, College of Medicine, The Ohio State University, Columbus, Ohio 43210
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Fonseca FV, Ravi K, Wiseman D, Tummala M, Harmon C, Ryzhov V, Fineman JR, Black SM. Mass spectroscopy and molecular modeling predict endothelial nitric oxide synthase dimer collapse by hydrogen peroxide through zinc tetrathiolate metal-binding site disruption. DNA Cell Biol 2010; 29:149-60. [PMID: 20184449 PMCID: PMC2883531 DOI: 10.1089/dna.2009.0858] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2009] [Revised: 10/17/2009] [Accepted: 10/19/2009] [Indexed: 01/24/2023] Open
Abstract
Endothelial nitric oxide synthase (eNOS) is inhibited by hydrogen peroxide (H(2)O(2)), but the mechanism has not been determined. Thus, the purpose of this study was to delineate the mechanism by which H(2)O(2) inhibits eNOS activity. Using mass spectroscopy, we found that the tetrathiolate cysteine residues 94 and 99 were susceptible to oxidation by H(2)O(2). Molecular modeling predicted that these cysteic acid modifications would disrupt the van der Waals interactions and the hydrogen bonding network mediated by the tetrathiolate cysteines 94 and 99 resulting in changes in quaternary structure, zinc release, and dimer collapse. Using recombinant human eNOS (heNOS) to test the predictions of the molecular modeling we found that H(2)O(2) caused disruption of the heNOS dimer and this was accompanied by zinc release and decreased NO generation. We also found that H(2)O(2) increased the oxidation of tetrahydrobiopterin (BH(4)) to dihydrobiopterin (BH(2)), whereas preincubation of heNOS with excess BH(4) prevented the destruction of zinc tetrathiolate and dimer collapse and preserved activity. Interestingly, we found that the dimmer-stabilizing effect of BH(4) is due to its ability to act as a catalase mimetic. Further, we confirmed that, in ovine aortic endothelial cells, H(2)O(2) could also induce dimer collapse and that increasing cellular BH(4) levels could maintain eNOS in its dimeric form and NO signaling when cells were challenged with H(2)O(2). This study links the inhibitory action of H(2)O(2) on heNOS through the destruction of zinc tetrathiolate metal-binding site and dimer collapse both in vitro and in vivo.
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Affiliation(s)
- Fabio V. Fonseca
- Vascular Biology Center, Medical College of Georgia, Augusta, Georgia
| | - Kandasamy Ravi
- Cold Spring Harbor Laboratories, Cold Spring Harbor, New York
| | - Dean Wiseman
- Vascular Biology Center, Medical College of Georgia, Augusta, Georgia
| | - Monorama Tummala
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois
| | - Cynthia Harmon
- Department of Pediatrics, University of California, San Francisco, California
| | - Victor Ryzhov
- Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois
| | - Jeffrey R. Fineman
- Department of Pediatrics, University of California, San Francisco, California
- Department of Cardiovascular Research Institute, University of California, San Francisco, California
| | - Stephen M. Black
- Vascular Biology Center, Medical College of Georgia, Augusta, Georgia
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19
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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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20
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Schulz E, Jansen T, Wenzel P, Daiber A, Münzel T. Nitric oxide, tetrahydrobiopterin, oxidative stress, and endothelial dysfunction in hypertension. Antioxid Redox Signal 2008; 10:1115-26. [PMID: 18321209 DOI: 10.1089/ars.2007.1989] [Citation(s) in RCA: 299] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Endothelial dysfunction in the setting of cardiovascular risk factors such as hypercholesterolemia, diabetes mellitus, chronic smoking, as well hypertension, is, at least in part, dependent of the production of reactive oxygen species (ROS) and the subsequent decrease in vascular bioavailability of nitric oxide (NO). ROS-producing enzymes involved in increased oxidative stress within vascular tissue include NADPH oxidase, xanthine oxidase, and mitochondrial superoxide producing enzymes. Superoxide produced by the NADPH oxidase may react with NO, thereby stimulating the production of the NO/superoxide reaction product peroxynitrite. Peroxynitrite in turn has been shown to uncouple eNOS, therefore switching an antiatherosclerotic NO producing enzyme to an enzyme that may accelerate the atherosclerotic process by producing superoxide. Increased oxidative stress in the vasculature, however, is not restricted to the endothelium and also occurs within the smooth muscle cell layer. Increased superoxide production has important consequences with respect to signaling by the soluble guanylate cyclase and the cGMP-dependent kinase I, which activity and expression is regulated in a redox-sensitive fashion. The present review will summarize current concepts concerning eNOS uncoupling, with special focus on the role of tetrahydrobiopterin in mediating eNOS uncoupling.
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Affiliation(s)
- Eberhard Schulz
- II Medizinische Klinik, Mainz, Kardiologie, Angiologie und Internistische Intensivmedizin, Mainz, Germany
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21
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Oxidative stress in vascular disease: causes, defense mechanisms and potential therapies. ACTA ACUST UNITED AC 2008; 5:338-49. [DOI: 10.1038/ncpcardio1211] [Citation(s) in RCA: 413] [Impact Index Per Article: 25.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2007] [Accepted: 02/01/2008] [Indexed: 02/07/2023]
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22
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Hardy M, Rockenbauer A, Vásquez-Vivar J, Felix C, Lopez M, Srinivasan S, Avadhani N, Tordo P, Kalyanaraman B. Detection, characterization, and decay kinetics of ROS and thiyl adducts of mito-DEPMPO spin trap. Chem Res Toxicol 2007; 20:1053-60. [PMID: 17559235 PMCID: PMC4455887 DOI: 10.1021/tx700101d] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report here the detection and characterization of spin adducts formed from the trapping of reactive oxygen species (superoxide and hydroxyl radicals) and glutathiyl and carbon-centered radicals by a newly synthesized nitrone, Mito-DEPMPO. This is a cationic nitrone spin trap with a triphenyl phosphonium cation conjugated to the DEPMPO analogue. The Mito-DEPMPO-OOH adduct, formed from the trapping of superoxide by Mito-DEPMPO, was enzymatically generated using xanthine/xanthine oxidase and neuronal nitric oxide synthase, and chemically generated by KO2 in 18-crown-6. The Mito-DEPMPO-OOH adduct exhibits an eight-line EPR spectrum with partial asymmetry arising from the alternate line-width effect. The half-life of the Mito-DEPMPO-OOH adduct is 2-2.5-times greater than that of the DEPMPO-OOH. The Mito-DEPMPO-SG adduct, formed from the trapping of glutathiyl radicals by Mito-DEPMPO, is 3-times more persistent than the analogue DEPMPO-SG adduct. In this study, we describe the EPR characterization of spin adducts formed from Mito-DEPMPO. The EPR parameters of Mito-DEPMPO adducts are distinctly different and highly characteristic. The detection of superoxide from an intact mitochondrion was feasible with Mito-DEPMPO but not with DEPMPO. We conclude that Mito-DEPMPO nitrone and its analogues are more effective than most nitrone spin traps for trapping superoxide, hydroxyl, and thiyl radicals formed in biological systems, including mitochondria.
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Affiliation(s)
| | | | | | | | | | | | | | | | - B. Kalyanaraman
- To whom correspondence should be addressed. Phone: 414-456-4129. Fax: 414-456-6512.
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23
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Förstermann U. Janus-faced role of endothelial NO synthase in vascular disease: uncoupling of oxygen reduction from NO synthesis and its pharmacological reversal. Biol Chem 2007; 387:1521-33. [PMID: 17132097 DOI: 10.1515/bc.2006.190] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Endothelial NO synthase (eNOS) is the predominant enzyme responsible for vascular NO synthesis. A functional eNOS transfers electrons from NADPH to its heme center, where L-arginine is oxidized to L-citrulline and NO. Common conditions predisposing to atherosclerosis, such as hypertension, hypercholesterolemia, diabetes mellitus and smoking, are associated with enhanced production of reactive oxygen species (ROS) and reduced amounts of bioactive NO in the vessel wall. NADPH oxidases represent major sources of ROS in cardiovascular pathophysiology. NADPH oxidase-derived superoxide avidly interacts with eNOS-derived NO to form peroxynitrite (ONOO(-)), which oxidizes the essential NOS cofactor (6R-)5,6,7,8-tetrahydrobiopterin (BH(4)). As a consequence, oxygen reduction uncouples from NO synthesis, thereby rendering NOS to a superoxide-producing pro-atherosclerotic enzyme. Supplementation with BH(4) corrects eNOS dysfunction in several animal models and in patients. Administration of high local doses of the antioxidant L-ascorbic acid (vitamin C) improves endothelial function, whereas large-scale clinical trials do not support a strong role for oral vitamin C and/or E in reducing cardiovascular disease. Statins, angiotensin-converting enzyme inhibitors and AT1 receptor blockers have the potential of reducing vascular oxidative stress. Finally, novel approaches are being tested to block pathways leading to oxidative stress (e.g. protein kinase C) or to upregulate antioxidant enzymes.
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Affiliation(s)
- Ulrich Förstermann
- Department of Pharmacology, Johannes Gutenberg University, D-55101 Mainz, Germany.
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24
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Abstract
Nitric oxide (NO*) is an important protective molecule in the vasculature, and endothelial NO* synthase (eNOS) is responsible for most of the vascular NO* produced. A functional eNOS oxidizes its substrate L-arginine to L-citrulline and NO*. This normal function of eNOS requires dimerization of the enzyme, the presence of the substrate L-arginine, and the essential cofactor (6R)-5,6,7,8-tetrahydro-L-biopterin (BH4), one of the most potent naturally occurring reducing agents. Cardiovascular risk factors such as hypertension, hypercholesterolemia, diabetes mellitus, or chronic smoking stimulate the production of reactive oxygen species in the vascular wall. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases represent major sources of this reactive oxygen species and have been found upregulated and activated in animal models of hypertension, diabetes, and sedentary lifestyle and in patients with cardiovascular risk factors. Superoxide (O2*-) reacts avidly with vascular NO* to form peroxynitrite (ONOO-). The cofactor BH4 is highly sensitive to oxidation by ONOO-. Diminished levels of BH4 promote O2*- production by eNOS (referred to as eNOS uncoupling). This transformation of eNOS from a protective enzyme to a contributor to oxidative stress has been observed in several in vitro models, in animal models of cardiovascular diseases, and in patients with cardiovascular risk factors. In many cases, supplementation with BH4 has been shown to correct eNOS dysfunction in animal models and patients. In addition, folic acid and infusions of vitamin C are able to restore eNOS functionality, most probably by enhancing BH4 levels as well.
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Affiliation(s)
- Ulrich Förstermann
- Department of Pharmacology, Johannes Gutenberg University, Mainz, Germany.
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25
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Jagnandan D, Sessa WC, Fulton D. Intracellular location regulates calcium-calmodulin-dependent activation of organelle-restricted eNOS. Am J Physiol Cell Physiol 2005; 289:C1024-33. [PMID: 15917301 DOI: 10.1152/ajpcell.00162.2005] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mislocalization of endothelial nitric oxide (NO) synthase (eNOS) in response to oxidized low-density lipoprotein, cholesterol depletion, elevated blood pressure, and bound eNOS interacting protein/NOS traffic inducer is associated with reduced NO release via unknown mechanisms. The proper targeting of eNOS to the plasma membrane or intracellular organelles is an important regulatory step controlling enzyme activity. Previous studies have shown that plasma membrane eNOS is constitutively phosphorylated on serine 1179 and highly active. In contrast, the activity of eNOS targeted to intracellular organelles is more complex. The cis-Golgi eNOS is fully activated by Akt-dependent phosphorylation. However, eNOS targeted to the trans-Golgi is decidedly less active in response to all modes of activation, including mutation to the phosphomimetic aspartic acid. In this study, we establish that when expressed within other intracellular organelles, such as the mitochondria and nucleus, the activity of eNOS is also greatly reduced. To address the mechanisms underlying the impaired catalytic activity of eNOS within these locations, we generated subcellular-targeted constructs that express a calcium-independent NOS isoform, iNOS. With the use of organelle specific (plasma membrane, cis- vs. trans-Golgi, plasma membrane, and Golgi, nucleus, and mitochondria) targeting motifs fused to the wild-type iNOS, we measured NO release from intact cells. With the exception of the Golgi lumen, our results showed no impairment in the ability of targeted iNOS to synthesize NO. Confirmation of correct targeting was obtained through confocal microscopy using identical constructs fused to the green fluorescent protein. We conclude that the reduced activation of eNOS within discrete cytoplasmic regions of the Golgi, the mitochondria and the nucleus is primarily due to insufficient access to calcium-calmodulin.
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Affiliation(s)
- Davin Jagnandan
- Vascular Biology Center and Department of Pharmacology, Medical College of Georgia, 1459 Laney Walker Blvd., Augusta Georgia 30912, USA
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27
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Suzuki T, Kurita H, Ichinose H. GTP cyclohydrolase I utilizes metal-free GTP as its substrate. EUROPEAN JOURNAL OF BIOCHEMISTRY 2004; 271:349-55. [PMID: 14717702 DOI: 10.1046/j.1432-1033.2003.03933.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
GTP cyclohydrolase I (GCH) is the rate-limiting enzyme for the synthesis of tetrahydrobiopterin and its activity is important in the regulation of monoamine neurotransmitters such as dopamine, norepinephrine and serotonin. We have studied the action of divalent cations on the enzyme activity of purified recombinant human GCH expressed in Escherichia coli. First, we showed that the enzyme activity is dependent on the concentration of Mg-free GTP. Inhibition of the enzyme activity by Mg2+, as well as by Mn2+, Co2+ or Zn2+, was due to the reduction of the availability of metal-free GTP substrate for the enzyme, when a divalent cation was present at a relatively high concentration with respect to GTP. We next examined the requirement of Zn2+ for enzyme activity by the use of a protein refolding assay, because the recombinant enzyme contained approximately one zinc atom per subunit of the decameric protein. Only when Zn2+ was present was the activity of the denatured enzyme effectively recovered by incubation with a chaperone protein. These are the first data demonstrating that GCH recognizes Mg-free GTP and requires Zn2+ for its catalytic activity. We suggest that the cellular concentration of divalent cations can modulate GCH activity, and thus tetrahydrobiopterin biosynthesis as well.
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Affiliation(s)
- Takahiro Suzuki
- Department of Life Science, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, Japan
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28
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Panda K, Adak S, Aulak KS, Santolini J, McDonald JF, Stuehr DJ. Distinct influence of N-terminal elements on neuronal nitric-oxide synthase structure and catalysis. J Biol Chem 2003; 278:37122-31. [PMID: 12847099 DOI: 10.1074/jbc.m304456200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nitric oxide (NO) is a signal molecule produced in animals by three different NO synthases. Of these, only NOS I (neuronal nitric-oxide synthase; nNOS) is expressed as catalytically active N-terminally truncated forms that are missing either an N-terminal leader sequence required for protein-protein interactions or are missing the leader sequence plus three core structural motifs that in other NOS are required for dimer assembly and catalysis. To understand how the N-terminal elements impact nNOS structure-function, we generated, purified, and extensively characterized variants that were missing the N-terminal leader sequence (Delta296nNOS) or missing the leader sequence plus the three core motifs (Delta349nNOS). Eliminating the leader sequence had no impact on nNOS structure or catalysis. In contrast, additional removal of the core elements weakened but did not destroy the dimer interaction, slowed ferric heme reduction and reactivity of a hemedioxy intermediate, and caused a 10-fold poorer affinity toward substrate l-arginine. This created an nNOS variant with slower and less coupled NO synthesis that is predisposed to generate reactive oxygen species along with NO. Our findings help justify the existence of nNOS N-terminal splice variants and identify specific catalytic changes that create functional differences among them.
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Affiliation(s)
- Koustubh Panda
- Department of Immunology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195, USA
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29
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Vanin AF, Huisman A, van Faassen EE. Iron dithiocarbamate as spin trap for nitric oxide detection: pitfalls and successes. Methods Enzymol 2003; 359:27-42. [PMID: 12481557 DOI: 10.1016/s0076-6879(02)59169-2] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- Anatoly F Vanin
- Institute of Chemical Physics, Russian Academy of Sciences, 119991 Moscow, Russia
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30
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Bird LE, Ren J, Zhang J, Foxwell N, Hawkins AR, Charles IG, Stammers DK. Crystal structure of SANOS, a bacterial nitric oxide synthase oxygenase protein from Staphylococcus aureus. Structure 2002; 10:1687-96. [PMID: 12467576 DOI: 10.1016/s0969-2126(02)00911-5] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Prokaryotic genes related to the oxygenase domain of mammalian nitric oxide synthases (NOSs) have recently been identified. Although they catalyze the same reaction as the eukaryotic NOS oxygenase domain, their biological function(s) are unknown. In order to explore rationally the biochemistry and evolution of the prokaryotic NOS family, we have determined the crystal structure of SANOS, from methicillin-resistant Staphylococcus aureus (MRSA), to 2.4 A. Haem and S-ethylisothiourea (SEITU) are bound at the SANOS active site, while the intersubunit site, occupied by the redox cofactor tetrahydrobiopterin (H(4)B) in mammalian NOSs, has NAD(+) bound in SANOS. In common with all bacterial NOSs, SANOS lacks the N-terminal extension responsible for stable dimerization in mammalian isoforms, but has alternative interactions to promote dimer formation.
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Affiliation(s)
- Louise E Bird
- Division of Structural Biology, The Wellcome Trust Centre for Human Genetics, Henry Wellcome Building of Genomic Medicine, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, United Kingdom
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31
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Panda K, Rosenfeld RJ, Ghosh S, Meade AL, Getzoff ED, Stuehr DJ. Distinct dimer interaction and regulation in nitric-oxide synthase types I, II, and III. J Biol Chem 2002; 277:31020-30. [PMID: 12048205 DOI: 10.1074/jbc.m203749200] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Homodimer formation activates all nitric-oxide synthases (NOSs). It involves the interaction between two oxygenase domains (NOSoxy) that each bind heme and (6R)-tetrahydrobiopterin (H4B) and catalyze NO synthesis from L-Arg. Here we compared three NOSoxy isozymes regarding dimer strength, interface composition, and the ability of L-Arg and H4B to stabilize the dimer, promote its formation, and protect it from proteolysis. Urea dissociation studies indicated that the relative dimer strengths were NOSIIIoxy >> NOSIoxy > NOSIIoxy (endothelial NOSoxy (eNOSoxy) >> neuronal NOSOXY (nNOSoxy) > inducible NOSoxy (iNOSoxy)). Dimer strengths of the full-length NOSs had the same rank order as judged by their urea-induced loss of NO synthesis activity. NOSoxy dimers containing L-Arg plus H4B exhibited the greatest resistance to urea-induced dissociation followed by those containing either molecule and then by those containing neither. Analysis of crystallographic structures of eNOSoxy and iNOSoxy dimers showed more intersubunit contacts and buried surface area in the dimer interface of eNOSoxy than iNOSoxy, thus revealing a potential basis for their different stabilities. L-Arg plus H4B promoted dimerization of urea-generated iNOSoxy and nNOSoxy monomers, which otherwise was minimal in their absence, and also protected both dimers against trypsin proteolysis. In these respects, L-Arg alone was more effective than H4B alone for nNOSoxy, whereas for iNOSoxy the converse was true. The eNOSoxy dimer was insensitive to proteolysis under all conditions. Our results indicate that the three NOS isozymes, despite their general structural similarity, differ markedly in their strengths, interfaces, and in how L-Arg and H4B influence their formation and stability. These distinguishing features may provide a basis for selective control and likely help to regulate each NOS in its particular biologic milieu.
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Affiliation(s)
- Koustubh Panda
- Department of Immunology, Lerner Research Institute, The Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195, USA
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Huisman A, Vos I, van Faassen EE, Joles JA, Gröne HJ, Martasek P, van Zonneveld AJ, Vanin AF, Rabelink TJ. Anti-inflammatory effects of tetrahydrobiopterin on early rejection in renal allografts: modulation of inducible nitric oxide synthase. FASEB J 2002; 16:1135-7. [PMID: 12039851 DOI: 10.1096/fj.01-0890fje] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Oxidative stress contributes to the development of early transplant failure. As nitric oxide synthases (NOS) can act as sources of superoxide, we investigated the effect of the NOS cofactor tetrahydrobiopterin (BH4) on oxyradical production and early rejection in a rat kidney transplantation model. Allograft transplantation (Brown Norway to Lewis) showed more renal superoxide production and monocyte infiltration when compared with isografts (Lewis to Lewis). Administration of the stable BH4 precursor sepiapterin had no effect on superoxide production in the isografts (51+/-10 vs. 69+/-17 cps/10 mg protein), but led to a marked decrease in superoxide production in the allografts (116+/-11 vs. 60+/-6 cps/10 mg protein; P<0.05) and was accompanied by a reduction in periarterial macrophage infiltration (3.3+/-0.7 vs. 1.3+/-0.3 cells/vessel; P<0.05) and an increase in NO production (78+/-22 vs. 173+/-12 AU/g kidney) (P<0.01). In vitro experiments confirm that iNOS can produce superoxide mainly from the heme domain, whereas BH4 administration can reverse this superoxide production in the presence of adequate anti-oxidant defense. Our findings support the hypothesis that BH4 can be used to modulate the function of the inflammatory iNOS isoform and suggest a potential therapeutic role for sepiapterin in early allograft rejection.
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Affiliation(s)
- Albert Huisman
- Department of Vascular Medicine, University Medical Center, Utrecht, The Netherlands
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Gorren ACF, Schmidt K, Mayer B. Binding of L-arginine and imidazole suggests heterogeneity of rat brain neuronal nitric oxide synthase. Biochemistry 2002; 41:7819-29. [PMID: 12056914 DOI: 10.1021/bi025675o] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Nitric oxide synthase (NOS) is inhibited by imidazole, which binds to the heme in a low-spin complex absorbing at 428 nm. Conversion by L-arginine of this complex into a high-spin species absorbing at 395 nm is a common method to determine the binding parameters of Arg. However, both Arg-competitive and noncompetitive inhibition of NOS by imidazole has been reported, and optical studies with neuronal NOS provided no evidence for imidazole affecting Arg binding. We investigated the cause for these paradoxical observations with recombinant rat brain neuronal NOS. Imidazole bound to nNOS with a K(d)(app) of 50 microM; tetrahydrobiopterin (BH4) lowered the affinity of nNOS for imidazole 4-fold. The enzyme behaved heterogeneously with respect to Arg binding. Most of nNOS (65-80%) showed competition between Arg and imidazole. In the presence of BH4, a K(d)(Arg) of 1 microM could be estimated for this fraction, as well as apparent association and dissociation rate constants of 2.5 x 10(6) M(-1) x s(-1) and 2.5 s(-1). A second fraction of nNOS (20-30%) exhibited little or no competition. Consequently, Arg binding did not cause dissociation of the imidazole complex for this fraction, and complete generation of the high-spin state by Arg could not be achieved in the presence of imidazole. A third fraction (< or =10%) bound Arg with low affinity (K(d) 1-2 mM). Because of this heterogeneity, titration curves with Arg became almost uninterpretable. We propose that this heterogeneous response of nNOS toward Arg and imidazole is underlying the apparently conflicting results reported in the literature.
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Affiliation(s)
- Antonius C F Gorren
- Institut für Pharmakologie und Toxikologie, Karl-Franzens-Universität Graz, Universitätsplatz 2, A-8010 Graz, Austria.
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Zou MH, Shi C, Cohen RA. Oxidation of the zinc-thiolate complex and uncoupling of endothelial nitric oxide synthase by peroxynitrite. J Clin Invest 2002. [DOI: 10.1172/jci0214442] [Citation(s) in RCA: 434] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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Zou MH, Shi C, Cohen RA. Oxidation of the zinc-thiolate complex and uncoupling of endothelial nitric oxide synthase by peroxynitrite. J Clin Invest 2002; 109:817-26. [PMID: 11901190 PMCID: PMC150913 DOI: 10.1172/jci14442] [Citation(s) in RCA: 200] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2001] [Accepted: 02/08/2002] [Indexed: 01/08/2023] Open
Abstract
Nitric oxide (NO) is produced by NO synthase (NOS) in many cells and plays important roles in the neuronal, muscular, cardiovascular, and immune systems. In various disease conditions, all three types of NOS (neuronal, inducible, and endothelial) are reported to generate oxidants through unknown mechanisms. We present here the first evidence that peroxynitrite (ONOO(-)) releases zinc from the zinc-thiolate cluster of endothelial NOS (eNOS) and presumably forms disulfide bonds between the monomers. As a result, disruption of the otherwise SDS-resistant eNOS dimers occurs under reducing conditions. eNOS catalytic activity is exquisitely sensitive to ONOO(-), which decreases NO synthesis and increases superoxide anion (O(2)(.-)) production by the enzyme. The reducing cofactor tetrahydrobiopterin is not oxidized, nor does it prevent oxidation of eNOS by the same low concentrations of OONO(-). Furthermore, eNOS derived from endothelial cells exposed to elevated glucose produces more O(2)(.-), and, like eNOS purified from diabetic LDL receptor-deficient mice, contains less zinc and fewer SDS-resistant dimers. Hence, eNOS exposure to oxidants including ONOO(-) causes increased enzymatic uncoupling and generation of O(2)(.-) in diabetes, contributing further to endothelial cell oxidant stress. Regulation of the zinc-thiolate center of NOS by ONOO(-) provides a novel mechanism for modulation of the enzyme function in disease.
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Affiliation(s)
- Ming-Hui Zou
- Vascular Biology Unit, Whitaker Cardiovascular Institute, Department of Medicine, Boston University School of Medicine, 650 Albany Street, Boston, MA 02118, USA.
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36
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Yoneyama H, Yamamoto A, Kosaka H. Neuronal nitric oxide synthase generates superoxide from the oxygenase domain. Biochem J 2001; 360:247-53. [PMID: 11696014 PMCID: PMC1222224 DOI: 10.1042/0264-6021:3600247] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
When l-arginine is depleted, neuronal nitric oxide synthase (nNOS) has been reported to generate superoxide. A flavoprotein module construct of nNOS has been demonstrated to be sufficient for superoxide production. In contrast, nNOS was reported not to be involved in superoxide formation, because such formation occurred with a mixture of the boiled enzyme and redox-active cofactors. We aimed to resolve these controversial issues by examining superoxide generation, without the addition of redox-active cofactors, by recombinant wild-type nNOS and by C415A-nNOS, which has a mutation in the haem proximal site. In a superoxide-sensitive adrenochrome assay, the initial lag period of C415A-nNOS was increased 2-fold compared with that of native nNOS. With ESR using the spin trap 5,5-dimethyl-1-pyrroline-N-oxide, prominent signals of the superoxide adduct were obtained with wild-type nNOS, whereas an enzyme preparation boiled for 5 min did not produce superoxide. Higher concentrations of NaCN (10 mM) decreased superoxide formation by 63%. Although the activity of the reductase domain was intact, superoxide generation from C415A-nNOS was decreased markedly, to only 10% of that of the wild-type enzyme. These results demonstrate that nNOS truly catalyses superoxide formation, that this involves the oxygenase domain, and that full-length nNOS hinders the reductase domain from producing superoxide.
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Affiliation(s)
- H Yoneyama
- The Second Department of Physiology, Kagawa Medical University, Miki-cho, Kita-gun, Kagawa 761-0793, Japan
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37
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Scheele JS, Bruner E, Zemojtel T, Martásek P, Roman LJ, Masters BS, Sharma VS, Magde D. Kinetics of CO and NO ligation with the Cys(331)-->Ala mutant of neuronal nitric-oxide synthase. J Biol Chem 2001; 276:4733-6. [PMID: 11067850 DOI: 10.1074/jbc.m007461200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nitric-oxide synthases (NOS) catalyze the conversion of l-arginine to NO, which then stimulates many physiological processes. In the active form, each NOS is a dimer; each strand has both a heme-binding oxygenase domain and a reductase domain. In neuronal NOS (nNOS), there is a conserved cysteine motif (CX(4)C) that participates in a ZnS(4) center, which stabilizes the dimer interface and/or the flavoprotein-heme domain interface. Previously, the Cys(331) --> Ala mutant was produced, and it proved to be inactive in catalysis and to have structural defects that disrupt the binding of l-Arg and tetrahydrobiopterin (BH(4)). Because binding l-Arg and BH(4) to wild type nNOS profoundly affects CO binding with little effect on NO binding, ligand binding to the mutant was characterized as follows. 1) The mutant initially has behavior different from native protein but reminiscent of isolated heme domain subchains. 2) Adding l-Arg and BH(4) has little effect immediately but substantial effect after extended incubation. 3) Incubation for 12 h restores behavior similar but not quite identical to that of wild type nNOS. Such incubation was shown previously to restore most but not all catalytic activity. These kinetic studies substantiate the hypothesis that zinc content is related to a structural rather than a catalytic role in maintaining active nNOS.
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Affiliation(s)
- J S Scheele
- Department of Medicine, University of Freiburg, D-79106 Freiburg, Germany
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38
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Smith SM, Sham C, Roman L, Martasek P, Salerno JC. Titration of low K(d) binding sites: binding of arginine analogs to nitric oxide synthases. Nitric Oxide 2001; 5:442-52. [PMID: 11587559 DOI: 10.1006/niox.2001.0372] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Spectrophotometrically monitored ligand titration is an important method for the determination of equilibrium dissociation constants (K(d)) from nitric oxide synthases (NOS). Low K(d) sites such as the tetrahydrobiopterin and arginine binding sites present difficulties in that experiments often require enzyme concentrations of the same magnitude as the K(d). An analytical method based on computer simulation is described that allows the estimation of K(d) values without an independent means of monitoring free ligand or without an accurate prior determination of the number of binding sites. The K(d) for arginine is approximately 0.5 microM for the tetrahydrobiopterin replete neuronal and inducible isoforms (nNOS and iNOS), while the endothelial isoform has a slightly higher K(d) (1.5 microM). N-OH-arginine (an intermediate) binds to nNOS with a K(d) of around 0.2 microM, while the inhibitors N-methyl-arginine and N-nitro-arginine bind more tightly; our best K(d) estimates are 100 nM or lower.
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Affiliation(s)
- S M Smith
- Biology Department, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
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39
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Lee SJ, Beckingham K, Stull JT. Mutations at lysine 525 of inducible nitric-oxide synthase affect its Ca2+-independent activity. J Biol Chem 2000; 275:36067-72. [PMID: 10978319 DOI: 10.1074/jbc.m003935200] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calmodulin binding to inducible nitric-oxide synthase may play an important role in its Ca(2+)-independent activity. Studies of inducible nitric-oxide synthase chimeras containing the calmodulin binding sequence of neuronal or endothelial nitric-oxide synthases show that the calmodulin binding sequence of inducible nitric-oxide synthase is necessary but not sufficient for the Ca(2+)-independent activity. The mutations at lysine 525 located at the C terminus of the calmodulin binding sequence of inducible nitric-oxide synthase were examined for the effects on the Ca(2+)-independent activity with chimeras containing the oxygenase or reductase domains of inducible or neuronal nitric-oxide synthases. Results show that the Ca(2+)-independent binding of calmodulin is not solely responsible for maximal Ca(2+)-independent activity of inducible nitric-oxide synthase. Lysine 525 of inducible nitric-oxide synthase may also play an important role in coordinating the maximal Ca(2+)-independent activity.
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Affiliation(s)
- S J Lee
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9040, USA.
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40
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Hemmens B, Goessler W, Schmidt K, Mayer B. Role of bound zinc in dimer stabilization but not enzyme activity of neuronal nitric-oxide synthase. J Biol Chem 2000; 275:35786-91. [PMID: 10954720 DOI: 10.1074/jbc.m005976200] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nitric-oxide synthases (NOS) are homodimeric proteins and can form an intersubunit Zn(4S) cluster. We have measured zinc bound to NOS purified from pig brain (0.6 mol/mol of NOS) and baculovirus-expressed rat neuronal NOS (nNOS) (0.49 +/- 0.13 mol/mol of NOS), by on-line gel-filtration/inductively coupled plasma mass spectrometry. Cobalt, manganese, molybdenum, nickel, and vanadium were all undetectable. Baculovirus-expressed nNOS also bound up to 2. 00 +/- 0.58 mol of copper/mol of NOS. Diethylenetriaminepentaacetic acid (DTPA) reduced the bound zinc to 0.28 +/- 0.07 and the copper to 0.97 +/- 0.24 mol/mol of NOS. Desalting of samples into thiol-free buffer did not affect the zinc content but completely eliminated the bound copper (</=0.02 mol/mol of NOS). Most (> or =75%) of the bound zinc was released from baculovirus-expressed rat nNOS by p-chloromercuriphenylsulfonic acid (PMPS). PMPS-treated nNOS was strongly (90 +/- 5%) inactivated. To isolate functional effects of zinc release from other effects of PMPS, PMPS-substituted thiols were unblocked by excess reduced thiol in the presence of DTPA, which hindered reincorporation of zinc. The resulting enzyme contained 0.12 +/- 0.05 mol of zinc but had a specific activity of 426 +/- 46 nmol of citrulline.mg(-1).min(-1), corresponding to 93 +/- 10% of non-PMPS-treated controls. PMPS also caused dissociation of nNOS dimers under native conditions, an effect that was blocked by the pteridine cofactor tetrahydrobiopterin (H(4)biopterin). H(4)biopterin did not affect zinc release. Even in the presence of H(4)biopterin, PMPS prevented conversion of NOS dimers to an SDS-resistant form. We conclude that zinc binding is a prerequisite for formation of SDS-resistant NOS dimers but is not essential for catalysis.
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Affiliation(s)
- B Hemmens
- Institut für Pharmakologie und Toxikologie, Karl-Franzens-Universität Graz, Universitätsplatz 2, and Institut für Chemie, Karl-Franzens-Universität Graz, Universitätsplatz 1, Graz A-8010, Austria
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41
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Yumoto T, Sagami I, Daff S, Shimizu T. Roles of the heme proximal side residues tryptophan409 and tryptophan421 of neuronal nitric oxide synthase in the electron transfer reaction. J Inorg Biochem 2000; 82:163-70. [PMID: 11132623 DOI: 10.1016/s0162-0134(00)00142-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Nitric oxide synthase (NOS) has an oxygenase domain with a thiol-coordinated heme active side similar to cytochrome P450. In contrast to cytochrome P450, however, conserved aromatic amino acids are situated in the heme proximal side of NOS. For example, in endothelial NOS (eNOS), the indole-ring nitrogen of Trp180 hydrogen-binds to the thiol of Cys186, the internal axial ligand to the heme. And, the aromatic side chain of Trp192 forms a bridge between this residue and the protein. Trp180 and Trp192 of eNOS correspond to Trp409 and Trp421 of neuronal NOS (nNOS), respectively. In order to understand the roles of the aromatic amino acids in catalysis, we generated Trp409His, Trp409Leu, Trp421His and Trp421Leu mutants of nNOS and determined their catalytic parameters. The Trp409Leu mutant was very poorly expressed in E. coli and was easily denatured during purification procedures. The NO formation activities of the Trp409His and Trp421Leu mutants were 11 and 25 micromol/min per micromol heme, respectively, and are lower than that (44 micromol/min per micromol heme) of the wild type. The activity (46 micromol/min per micromol heme) of the Trp421His mutant was comparable to that of the wild-type enzyme. However, NADPH oxidation rates of Trp421His (230 micromol/min per micromol heme) and Trp421Leu (104 micromol/min per microol heme) in the presence of L-Arg were much larger than those observed for the wild type (65 micromol/min per micromol heme) and the Trp409His mutant (43 micromol/min per micromol heme). The cytochrome c reduction rate of the Trp421His mutant was 6-fold larger than that of the wild type. The heme reduction rate with NADPH for the Trp421His mutant (0.09 min(-1)) was much lower than that (1.0 min(-1)) of the wild type. Taken together, it appears that Trp421 may be involved in inter-domain/inter-subunit electron transfer reactions.
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Affiliation(s)
- T Yumoto
- Institute for Chemical Reaction Science, Tohoku University, Sendai, Japan
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42
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Montgomery HJ, Romanov V, Guillemette JG. Removal of a putative inhibitory element reduces the calcium-dependent calmodulin activation of neuronal nitric-oxide synthase. J Biol Chem 2000; 275:5052-8. [PMID: 10671547 DOI: 10.1074/jbc.275.7.5052] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Neuronal nitric-oxide synthase (NOS) and endothelial NOS are constitutive NOS isoforms that are activated by binding calmodulin in response to elevated intracellular calcium. In contrast, the inducible NOS isoform binds calmodulin at low basal levels of calcium in resting cells. Primary sequence comparisons show that each constitutive NOS isozyme contains a polypeptide segment within its reductase domain, which is absent in the inducible NOS enzyme. To study a possible link between the presence of these additional polypeptide segments in constitutive NOS enzymes and their calcium-dependent calmodulin activation, three deletion mutants were created. The putative inhibitory insert was removed from the FMN binding regions of the neuronal NOS holoenzyme and from two truncated neuronal NOS reductase enzymes in which the calmodulin binding region was either included or deleted. All three mutant enzymes showed reduced incorporation of FMN and required reconstitution with exogenous FMN for activity. The combined removal of both the calmodulin binding domain and the putative inhibitory insert did not result in a calmodulin-independent neuronal NOS reductase. Thus, although the putative inhibitory element has an effect on the calcium-dependent calmodulin activation of neuronal NOS, it does not have the properties of the typical autoinhibitory domain found in calmodulin-activated enzymes.
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Affiliation(s)
- H J Montgomery
- Department of Chemistry and the Guelph Waterloo Centre for Graduate Work in Chemistry and Biochemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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43
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Masters BS. Structural Variations to Accommodate Functional Themes of the Isoforms of NO Synthases. Nitric Oxide 2000. [DOI: 10.1016/b978-012370420-7/50007-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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44
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45
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Structures of gas-generating heme enzymes: Nitric oxide synthase and heme oxygenase. ADVANCES IN INORGANIC CHEMISTRY 2000. [DOI: 10.1016/s0898-8838(00)51005-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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46
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Sono M, Ledbetter AP, McMillan K, Roman LJ, Shea TM, Masters BS, Dawson JH. Essential thiol requirement to restore pterin- or substrate-binding capability and to regenerate native enzyme-type high-spin heme spectra in the Escherichia coli-expressed tetrahydrobiopterin-free oxygenase domain of neuronal nitric oxide synthase. Biochemistry 1999; 38:15853-62. [PMID: 10625450 DOI: 10.1021/bi991580j] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nitric oxide (NO) synthases (NOS) are thiolate-ligated heme-, tetrahydrobiopterin (BH(4))-, and flavin-containing monooxygenases which catalyze the NADPH-dependent conversion of L-arginine (L-Arg) to NO AND citrulline. NOS consists of two domains: an N-terminal oxygenase (heme- and BH(4)-bound) domain and a C-terminal reductase (FMN- and FAD-bound) domain. In this study, we have spectroscopically examined the binding of L-Agr and BH(4) to the dimeric, BH(4)-free ferric neuronal NOS (NNOS) oxygenase domain expressed in Escherichia coli separately from the reductase domain. Addition of L-Arg or its analogue inhibitors (N(G)()-methyl-L-Arg, N(G)()-nitro-L-Arg) and BH(4), together with dithiothreitol (DTT), to the pterin-free ferric low-spin oxygenase domain (gamma(MAX): 419, 538, 568 NM) and incubation for 2-3 days at 4 degrees C converted the domain to a native enzyme-type, predominantly high-spin state (gamma(MAX): approximately 395, approximately 512, approximately 650 NM). 7,8-Dihydrobiopterin and other thiols (E.G., beta-mercaptoethanol, cysteine, and glutathione, with less effectiveness) can replace BH(4) and DTT, respectively. the UV-visible absorption spectrum of L-Arg-bound ferric full length NNOS, which exhibits a relatively intense band at approximately 650 NM (epsilon equals 7.5-8 MM(-)(1) CM(-)(1)) due to the presence of a neutral flavin semiquinone, can then be quantitatively reconstructed by combining the spectra of equimolar amounts of the oxygenase and reductase domains. Of particular note, the heme spin-state conversion does not occur in the absence of a thiol even after prolonged (35-48 H) incubation of the oxygenase domain with BH(4) and/or L-Arg under anaerobic conditions. Thus, DTT (or other thiols) plays a significant role(s) beyond keeping BH(4) in its reduced form, In restoring the pterin- and/or substrate-binding capability of the E. coli-expressed, BH(4) free, dimeric NNOS oxygenase domain. Our results in combination with recently available X-ray crystallography and site-directed mutagenesis data suggest that the observed DTT effects arise from the involvement of an intersubunit disulfide bond or its rearrangement in the NOS dimer.
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Affiliation(s)
- M Sono
- Department of Chemistry and Biochemistry and School of Medicine, University of South Carolina, Columbia, South Carolina 29208, USA.
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47
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Vásquez-Vivar J, Hogg N, Martásek P, Karoui H, Pritchard KA, Kalyanaraman B. Tetrahydrobiopterin-dependent inhibition of superoxide generation from neuronal nitric oxide synthase. J Biol Chem 1999; 274:26736-42. [PMID: 10480877 DOI: 10.1074/jbc.274.38.26736] [Citation(s) in RCA: 144] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The binding of calcium/calmodulin stimulates electron transfer between the reductase and oxygenase domains of neuronal nitric oxide synthase (nNOS). Here, we demonstrate using electron spin resonance spin-trapping with 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide that pterin-free nNOS generates superoxide from the reductase and the oxygenase domain by a calcium/calmodulin-dependent mechanism. Tetrahydrobiopterin (BH(4)) diminishes the formation of superoxide by a mechanism that does not cause inhibition of NADPH consumption. In contrast, BH(4) analogs 7,8-dihydrobiopterin and sepiapterin do not affect superoxide yields. L-Arginine alone inhibits the generation of superoxide by nNOS but not by C331A-nNOS mutant that has a low affinity for L-arginine. A greater decrease in superoxide yields is observed when nNOS is preincubated with L-arginine. This effect is in accordance with the slow binding rates of L-arginine to NOS in the absence of BH(4). L-Arginine alone or in combination with BH(4) decreases the rates of NADPH consumption. The effect of L-arginine on superoxide yields, however, was less dramatic than that caused by BH(4) as much higher concentrations of L-arginine are necessary to attain the same inhibition. In combination, L-arginine and BH(4) inhibit the formation of superoxide generation and stimulate the formation of L-citrulline. We conclude that, in contrast to L-arginine, BH(4) does not inhibit the generation of superoxide by controlling electron transfer through the enzyme but by stimulating the formation of the heme-peroxo species.
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Affiliation(s)
- J Vásquez-Vivar
- Department of Pathology, Cardiovascular Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA
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48
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Shimanuki T, Sato H, Daff S, Sagami I, Shimizu T. Crucial role of Lys(423) in the electron transfer of neuronal nitric-oxide synthase. J Biol Chem 1999; 274:26956-61. [PMID: 10480907 DOI: 10.1074/jbc.274.38.26956] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [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 composed of an oxygenase domain having cytochrome P450-type heme active site and a reductase domain having FAD- and FMN-binding sites. To investigate the route of electron transfer from the reductase domain to the heme, we generated mutants at Lys(423) in the heme proximal site of neuronal NOS and examined the catalytic activities, electron transfer rates, and NADPH oxidation rates. A K423E mutant showed no NO formation activity (<0.1 nmol/min/nmol heme), in contrast with that (72 nmol/min/nmol heme) of the wild type enzyme. The electron transfer rate (0.01 min(-1)) of the K423E on addition of excess NADPH was much slower than that (>10 min(-1)) of the wild type enzyme. From the crystal structure of the oxygenase domain of endothelial NOS, Lys(423) of neuronal NOS is likely to interact with Trp(409) which lies in contact with the heme plane and with Cys(415), the axial ligand. It is also exposed to solvent and lies in the region where the heme is closest to the protein surface. Thus, it seems likely that ionic interactions between Lys(423) and the reductase domain may help to form a flavin to heme electron transfer pathway.
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Affiliation(s)
- T Shimanuki
- Institute for Chemical Reaction Science, Tohoku University, Sendai 980-8577, Japan
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49
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Rodríguez-Crespo I, Nishida CR, Knudsen GM, de Montellano PR. Mutation of the five conserved histidines in the endothelial nitric-oxide synthase hemoprotein domain. No evidence for a non-heme metal requirement for catalysis. J Biol Chem 1999; 274:21617-24. [PMID: 10419469 DOI: 10.1074/jbc.274.31.21617] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Five conserved histidine residues are found in the human endothelial nitric-oxide synthase (NOS) heme domain: His-420, His-421, and His-461 are close to the heme, whereas His-146 and His-214 are some distance away. To investigate whether the histidines form a non-heme iron-binding site, we have expressed the H146A, H214A, H420A, H421A, and H461A mutants. The H420A mutant could not be isolated, and the H146A and H421A mutants were inactive. The H214A mutant resembled the wild-type enzyme in all respects. The H461A mutant had a low-spin heme, but high concentrations of L-Arg and tetrahydrobiopterin led to partial recovery of activity. Laser atomic emission showed that the only significant metal in NOS other than calcium and iron is zinc. The activities of the NOS isoforms were not increased by incubation with Fe(2+), but were inhibited by high Fe(2+) or Zn(2+) concentrations. The histidine mutations altered the ability of the protein to dimerize and to bind heme. However, the protein metal content, the inability of exogenous Fe(2+) to increase catalytic activity, and the absence of evidence that the conserved histidines form a metal site provide no support for a catalytic role for a non-heme redox-active metal.
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Affiliation(s)
- I Rodríguez-Crespo
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain
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Li H, Raman CS, Glaser CB, Blasko E, Young TA, Parkinson JF, Whitlow M, Poulos TL. Crystal structures of zinc-free and -bound heme domain of human inducible nitric-oxide synthase. Implications for dimer stability and comparison with endothelial nitric-oxide synthase. J Biol Chem 1999; 274:21276-84. [PMID: 10409685 DOI: 10.1074/jbc.274.30.21276] [Citation(s) in RCA: 152] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The crystal structures of the heme domain of human inducible nitric-oxide synthase (NOS-2) in zinc-free and -bound states have been solved. In the zinc-free structure, two symmetry-related cysteine residues form a disulfide bond. In the zinc-bound state, these same two cysteine residues form part of a zinc-tetrathiolate (ZnS(4)) center indistinguishable from that observed in the endothelial isoform (NOS-3). As in NOS-3, ZnS(4) plays a key role in stabilizing intersubunit contacts and in maintaining the integrity of the cofactor (tetrahydrobiopterin) binding site of NOS-2. A comparison of NOS-2 and NOS-3 structures illustrates the conservation of quaternary structure, tertiary topology, and substrate and cofactor binding sites, in addition to providing insights on isoform-specific inhibitor design. The structural comparison also reveals that pterin binding does not preferentially stabilize the dimer interface of NOS-2 over NOS-3.
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Affiliation(s)
- H Li
- Department of Molecular Biology and Biochemistry, University of California at Irvine, Irvine, California 92697, USA
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