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Biophysical and structural investigation of the regulation of human GTP cyclohydrolase I by its regulatory protein GFRP. J Struct Biol 2020; 213:107691. [PMID: 33387654 DOI: 10.1016/j.jsb.2020.107691] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2020] [Revised: 12/22/2020] [Accepted: 12/24/2020] [Indexed: 11/23/2022]
Abstract
GTP Cyclohydrolase I (GCH1) catalyses the conversion of guanosine triphosphate (GTP) to dihydroneopterin triphosphate (H2NTP), the initiating step in the biosynthesis of tetrahydrobiopterin (BH4). BH4 functions as co-factor in neurotransmitter biosynthesis. BH4 homeostasis is a promising target to treat pain disorders in patients. The function of mammalian GCH1s is regulated by a metabolic sensing mechanism involving a regulator protein, GCH1 feedback regulatory protein (GFRP). Dependent on the relative cellular concentrations of effector ligands, BH4 and phenylalanine, GFRP binds GCH1 to form inhibited or activated complexes, respectively. We determined high-resolution structures of the ligand-free and -bound human GFRP and GCH1-GFRP complexes by X-ray crystallography. Highly similar binding modes of the substrate analogue 7-deaza-GTP to active and inhibited GCH1-GFRP complexes confirm a novel, dissociation rate-controlled mechanism of non-competitive inhibition to be at work. Further, analysis of all structures shows that upon binding of the effector molecules, the conformations of GCH1 or GFRP are altered and form highly complementary surfaces triggering a picomolar interaction of GFRP and GCH1 with extremely slow koff values, while GCH1-GFRP complexes rapidly disintegrate in absence of BH4 or phenylalanine. Finally, comparing behavior of full-length and N-terminally truncated GCH1 we conclude that the disordered GCH1 N-terminus does not have impact on complex formation and enzymatic activity. In summary, this comprehensive and methodologically diverse study helps to provide a better understanding of the regulation of GCH1 by GFRP and could thus stimulate research on GCH1 modulating drugs.
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2
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Ebenhoch R, Prinz S, Kaltwasser S, Mills DJ, Meinecke R, Rübbelke M, Reinert D, Bauer M, Weixler L, Zeeb M, Vonck J, Nar H. A hybrid approach reveals the allosteric regulation of GTP cyclohydrolase I. Proc Natl Acad Sci U S A 2020; 117:31838-31849. [PMID: 33229582 PMCID: PMC7750480 DOI: 10.1073/pnas.2013473117] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Guanosine triphosphate (GTP) cyclohydrolase I (GCH1) catalyzes the conversion of GTP to dihydroneopterin triphosphate (H2NTP), the initiating step in the biosynthesis of tetrahydrobiopterin (BH4). Besides other roles, BH4 functions as cofactor in neurotransmitter biosynthesis. The BH4 biosynthetic pathway and GCH1 have been identified as promising targets to treat pain disorders in patients. The function of mammalian GCH1s is regulated by a metabolic sensing mechanism involving a regulator protein, GCH1 feedback regulatory protein (GFRP). GFRP binds to GCH1 to form inhibited or activated complexes dependent on availability of cofactor ligands, BH4 and phenylalanine, respectively. We determined high-resolution structures of human GCH1-GFRP complexes by cryoelectron microscopy (cryo-EM). Cryo-EM revealed structural flexibility of specific and relevant surface lining loops, which previously was not detected by X-ray crystallography due to crystal packing effects. Further, we studied allosteric regulation of isolated GCH1 by X-ray crystallography. Using the combined structural information, we are able to obtain a comprehensive picture of the mechanism of allosteric regulation. Local rearrangements in the allosteric pocket upon BH4 binding result in drastic changes in the quaternary structure of the enzyme, leading to a more compact, tense form of the inhibited protein, and translocate to the active site, leading to an open, more flexible structure of its surroundings. Inhibition of the enzymatic activity is not a result of hindrance of substrate binding, but rather a consequence of accelerated substrate binding kinetics as shown by saturation transfer difference NMR (STD-NMR) and site-directed mutagenesis. We propose a dissociation rate controlled mechanism of allosteric, noncompetitive inhibition.
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Affiliation(s)
- Rebecca Ebenhoch
- Medicinal Chemistry, Boehringer Ingelheim Pharma GmbH & Co. KG, 88397 Biberach an der Riss, Germany
| | - Simone Prinz
- Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Susann Kaltwasser
- Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Deryck J Mills
- Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Robert Meinecke
- Medicinal Chemistry, Boehringer Ingelheim Pharma GmbH & Co. KG, 88397 Biberach an der Riss, Germany
| | - Martin Rübbelke
- Medicinal Chemistry, Boehringer Ingelheim Pharma GmbH & Co. KG, 88397 Biberach an der Riss, Germany
| | - Dirk Reinert
- Medicinal Chemistry, Boehringer Ingelheim Pharma GmbH & Co. KG, 88397 Biberach an der Riss, Germany
| | - Margit Bauer
- Medicinal Chemistry, Boehringer Ingelheim Pharma GmbH & Co. KG, 88397 Biberach an der Riss, Germany
| | - Lisa Weixler
- Medicinal Chemistry, Boehringer Ingelheim Pharma GmbH & Co. KG, 88397 Biberach an der Riss, Germany
| | - Markus Zeeb
- Medicinal Chemistry, Boehringer Ingelheim Pharma GmbH & Co. KG, 88397 Biberach an der Riss, Germany
| | - Janet Vonck
- Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Herbert Nar
- Medicinal Chemistry, Boehringer Ingelheim Pharma GmbH & Co. KG, 88397 Biberach an der Riss, Germany;
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3
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Nasser A, Møller AT, Hellmund V, Thorborg SS, Jespersgaard C, Bjerrum OJ, Dupont E, Nachman G, Lykkesfeldt J, Jensen TS, Møller LB. Heterozygous mutations in GTP-cyclohydrolase-1 reduce BH4 biosynthesis but not pain sensitivity. Pain 2018; 159:1012-1024. [PMID: 29470312 DOI: 10.1097/j.pain.0000000000001175] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Human studies have demonstrated a correlation between noncoding polymorphisms of "the pain protective" haplotype in the GCH1 gene that encodes for GTP cyclohydrolase I (GTPCH1)-which leads to reduced tetrahydrobiopterin (BH4) production in cell systems-and a diminished perception of experimental and clinical pain. Here, we investigate whether heterozygous mutations in the GCH1 gene which lead to a profound BH4 reduction in patients with dopa-responsive dystonia (DRD) have any effect on pain sensitivity. The study includes an investigation of GCH1-associated biomarkers and pain sensitivity in a cohort of 22 patients with DRD and 36 controls. The patients with DRD had, when compared with controls, significantly reduced levels of BH4, neopterin, biopterin, and GTPCH1 in their urine, blood, or cytokine-stimulated fibroblasts, but their pain response with respect to non-painful stimulation, (acute) stimulus-evoked pain, or pain response after capsaicin-induced sensitization was not significantly different. A family-specific cohort of 11 patients with DRD and 11 controls were included in this study. The patients with DRD were heterozygous for the pain protective haplotype in cis with the GCH1 disease-causing mutation, c.899T>C. No effect on pain perception was observed for this combined haplotype. In conclusion, a reduced concentration of BH4 is not sufficient to alter ongoing pain sensitivity or evoked pain responses.
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Affiliation(s)
- Arafat Nasser
- Applied Human Molecular Genetics, Clinical Genetic Clinic, Kennedy Center, Copenhagen University Hospital, Rigshospitalet, Glostrup, Denmark
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen Ø, Denmark
| | - Anette Torvin Møller
- Department of Neurology, Danish Pain Research Center, Aarhus University Hospital, Århus, Denmark
| | - Vibe Hellmund
- Department of Neurology, Danish Pain Research Center, Aarhus University Hospital, Århus, Denmark
| | - Sidsel Salling Thorborg
- Applied Human Molecular Genetics, Clinical Genetic Clinic, Kennedy Center, Copenhagen University Hospital, Rigshospitalet, Glostrup, Denmark
| | - Cathrine Jespersgaard
- Applied Human Molecular Genetics, Clinical Genetic Clinic, Kennedy Center, Copenhagen University Hospital, Rigshospitalet, Glostrup, Denmark
| | - Ole J Bjerrum
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen Ø, Denmark
| | - Erik Dupont
- Department of Neurology, Aarhus University Hospital, Århus, Denmark
| | - Gösta Nachman
- Department of Biology, Section of Ecology and Evolution, University of Copenhagen, Copenhagen Ø, Denmark
| | - Jens Lykkesfeldt
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark
| | - Troels Staehelin Jensen
- Department of Neurology, Danish Pain Research Center, Aarhus University Hospital, Århus, Denmark
| | - Lisbeth Birk Møller
- Applied Human Molecular Genetics, Clinical Genetic Clinic, Kennedy Center, Copenhagen University Hospital, Rigshospitalet, Glostrup, Denmark
- Department of Science and Environment, Roskilde University, Roskilde, Denmark
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4
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Cheema AK, Pathak R, Zandkarimi F, Kaur P, Alkhalil L, Singh R, Zhong X, Ghosh S, Aykin-Burns N, Hauer-Jensen M. Liver metabolomics reveals increased oxidative stress and fibrogenic potential in gfrp transgenic mice in response to ionizing radiation. J Proteome Res 2014; 13:3065-74. [PMID: 24824572 PMCID: PMC4053308 DOI: 10.1021/pr500278t] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
![]()
Although radiation-induced tissue-specific
injury is well documented,
the underlying molecular changes resulting in organ dysfunction and
the consequences thereof on overall metabolism and physiology have
not been elucidated. We previously reported the generation and characterization
of a transgenic mouse strain that ubiquitously overexpresses Gfrp
(GTPH-1 feedback regulatory protein) and exhibits higher oxidative
stress, which is a possible result of decreased tetrahydrobiopterin
(BH4) bioavailability. In this study, we report genotype-dependent
changes in the metabolic profiles of liver tissue after exposure to
nonlethal doses of ionizing radiation. Using a combination of untargeted
and targeted quantitative mass spectrometry, we report significant
accumulation of metabolites associated with oxidative stress, as well
as the dysregulation of lipid metabolism in transgenic mice after
radiation exposure. The radiation stress seems to exacerbate lipid
peroxidation and also results in higher expression of genes that facilitate
liver fibrosis, in a manner that is dependent on the genetic background
and post-irradiation time interval. These findings suggest the significance
of Gfrp in regulating redox homeostasis in response to stress induced
by ionizing radiation affecting overall physiology.
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Affiliation(s)
- Amrita K Cheema
- Departments of Oncology, ‡Biochemistry, Molecular and Cellular Biology, and ∥Department of Biostatistics, Bioinformatics and Biomathematics, Georgetown University Medical Center , Washington DC 20057, United States
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5
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McHugh PC, Joyce PR, Deng X, Kennedy MA. A polymorphism of the GTP-cyclohydrolase I feedback regulator gene alters transcriptional activity and may affect response to SSRI antidepressants. THE PHARMACOGENOMICS JOURNAL 2011; 11:207-13. [PMID: 20351752 DOI: 10.1038/tpj.2010.23] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2009] [Revised: 01/03/2010] [Accepted: 02/28/2010] [Indexed: 11/09/2022]
Abstract
Tetrahydrobiopterin (BH(4)) is an essential cofactor for synthesis of many neurotransmitters including serotonin. In serotonergic neurons, BH(4) is tightly regulated by GTP-cyclohydrolase I feedback regulator (GFRP). Given the pivotal role of the serotonergic system in mood disorders and selective serotonin reuptake inhibitors (SSRIs) antidepressant function, we tested the hypothesis that GFRP gene (GCHFR) variants would modify response to antidepressants in subjects with major depression. Two single nucleotide polymorphisms (rs7164342 and rs7163862) in the GCHFR promoter were identified and occurred as two haplotypes (GA or TT). A multiple regression analysis revealed that homozygous individuals for the TT haplotype were less likely to respond to the SSRI fluoxetine than to the tricyclic antidepressant nortriptyline (P = 0.037). Moreover, the TT haplotype showed a reduced transcription rate in luciferase reporter gene assays, which may impact on BH(4)-mediated neurotransmitter production, thus suggesting a biological process through which GCHFR promoter variants might influence antidepressant response.
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Affiliation(s)
- P C McHugh
- Department of Pathology, University of Otago, Christchurch, New Zealand.
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7
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Adaptive copy number evolution in malaria parasites. PLoS Genet 2008; 4:e1000243. [PMID: 18974876 PMCID: PMC2570623 DOI: 10.1371/journal.pgen.1000243] [Citation(s) in RCA: 153] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2008] [Accepted: 09/29/2008] [Indexed: 11/19/2022] Open
Abstract
Copy number polymorphism (CNP) is ubiquitous in eukaryotic genomes, but the degree to which this reflects the action of positive selection is poorly understood. The first gene in the Plasmodium folate biosynthesis pathway, GTP-cyclohydrolase I (gch1), shows extensive CNP. We provide compelling evidence that gch1 CNP is an adaptive consequence of selection by antifolate drugs, which target enzymes downstream in this pathway. (1) We compared gch1 CNP in parasites from Thailand (strong historical antifolate selection) with those from neighboring Laos (weak antifolate selection). Two percent of chromosomes had amplified copy number in Laos, while 72% carried multiple (2–11) copies in Thailand, and differentiation exceeded that observed at 73 synonymous SNPs. (2) We found five amplicon types containing one to greater than six genes and spanning 1 to >11 kb, consistent with parallel evolution and strong selection for this gene amplification. gch1 was the only gene occurring in all amplicons suggesting that this locus is the target of selection. (3) We observed reduced microsatellite variation and increased linkage disequilibrium (LD) in a 900-kb region flanking gch1 in parasites from Thailand, consistent with rapid recent spread of chromosomes carrying multiple copies of gch1. (4) We found that parasites bearing dhfr-164L, which causes high-level resistance to antifolate drugs, carry significantly (p = 0.00003) higher copy numbers of gch1 than parasites bearing 164I, indicating functional association between genes located on different chromosomes but linked in the same biochemical pathway. These results demonstrate that CNP at gch1 is adaptive and the associations with dhfr-164L strongly suggest a compensatory function. More generally, these data demonstrate how selection affects multiple enzymes in a single biochemical pathway, and suggest that investigation of structural variation may provide a fast-track to locating genes underlying adaptation. Recent comparative genomic hybridization studies have revealed extensive copy number variation in eukaryotic genomes. The first gene in the Plasmodium folate biosynthesis pathway, GTP-cyclohydrolase I (gch1), shows extensive copy number polymorphism (CNP). We provide compelling evidence that gch1 CNP is adaptive and most likely results from selection by antifolate drugs, which target enzymes downstream in this pathway. Gch1 CNP shows extreme geographical differentiation; hitchhiking reduces diversity and increases LD in flanking sequence, indicating recent rapid spread within Thailand, while amplicon structure reveals multiple origins and parallel evolution. Furthermore, strong association between elevated copy number and a critical mutation dhfr-I164L that underlies high-level antifolate resistance indicates functional linkage and fitness epistasis between genes on different chromosomes. These data reveal hidden complexity in the evolutionary response to antifolate treatment and demonstrate that analysis of structural variation can provide a fast-track to locating genes that underlie adaptation.
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8
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Vásquez-Vivar J, Whitsett J, Ionova I, Konorev E, Zielonka J, Kalyanaraman B, Shi Y, Pieper GM. Cytokines and lipopolysaccharides induce inducible nitric oxide synthase but not enzyme activity in adult rat cardiomyocytes. Free Radic Biol Med 2008; 45:994-1001. [PMID: 18634867 PMCID: PMC2578873 DOI: 10.1016/j.freeradbiomed.2008.06.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Revised: 05/28/2008] [Accepted: 06/18/2008] [Indexed: 12/24/2022]
Abstract
There is evidence that nitric oxide (NO) formation in adult cardiomyocytes stimulated with lipopolysaccharide (LPS) is not commensurate with iNOS levels. Tetrahydrobiopterin (BH(4)) is a key factor in the stabilization and NO production by iNOS homodimer. Thus we hypothesized that BH(4) is a limiting factor for NO production in adult cardiomyocytes in response to LPS and cytokines (TNF-alpha, IL-1, IFN-gamma alone, or mixed). It was verified that LPS and cytokines induced iNOS expression which did not translate into increased nitrite or [(14)C]citrulline production. This response coincided with defective BH(4) synthesis and low GTP cyclohydrolase activity. Furthermore, supplementation with BH(4) and ascorbate failed to increase iNOS activity. This effect was related to preferential accumulation of BH(2) rather than BH(4) in these cells. Uncoupled iNOS activity in stimulated cells was examined using mitochondrial aconitase activity as an endogenous marker of superoxide anion radical (O(2)(-)) formation, and found not to be significantly inhibited. 2-Hydroxyethidium also was not significantly increased. We conclude that adult cardiomyocytes are an unlikely source of NO and O(2)(-) in inflammatory conditions. This finding adds a new and unexpected layer of complexity to our understanding of the responses of the adult heart to inflammation.
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9
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10
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Kalivendi S, Hatakeyama K, Whitsett J, Konorev E, Kalyanaraman B, Vásquez-Vivar J. Changes in tetrahydrobiopterin levels in endothelial cells and adult cardiomyocytes induced by LPS and hydrogen peroxide--a role for GFRP? Free Radic Biol Med 2005; 38:481-91. [PMID: 15649650 DOI: 10.1016/j.freeradbiomed.2004.11.004] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/23/2004] [Revised: 10/29/2004] [Accepted: 11/01/2004] [Indexed: 11/30/2022]
Abstract
Alterations in tetrahydrobiopterin (BH4) levels have significant consequences in vascular pathophysiology. However, the mechanisms regulating BH4 remain poorly understood. The activity of GTP cyclohydrolase I (GTPCH-I), the first enzyme in BH4 biosynthesis, is controlled by protein levels, posttranslational modifications and interaction with GTPCH-I feedback regulatory protein (GFRP). This work examined the correlation between GTPCH-I protein levels and activity and changes in BH4 in human endothelial cells (HAECs) and adult rat cardiomyocytes (ARCM). Changes in BH4 were stimulated with LPS in HAECs and ARCM, and with hydrogen peroxide in HAECs only. Biopterin production by HAECs and ARCM were attained with concentrations of LPS >>1 microg/ml and responses were nonlinear with respect to LPS concentrations. Western blot analysis demonstrated that induction of biopterin synthesis in HAECs and ARCM by LPS does not entail augmentation of constitutive GTPCH-I protein levels. However, LPS diminished GFRP mRNA, suggesting that disruption of GTPCH-I:GFRP complex enhances de novo biopterin synthesis. Conversely, treatment with hydrogen peroxide increased GTPCH-I and GFRP mRNA levels in HAECs while depleting BH4 and GSH, which was counteracted by catalase. This indicates that GFRP may override increases in GTPCH-I protein inhibiting enzyme activity. This conclusion is further supported by depletion of biopterin in cells transiently transfected with GFRP. Thus, allosteric regulation of GTPCH-I activity in the cardiovascular system maybe an important mechanism regulating BH4 levels through GFRP signaling.
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Affiliation(s)
- Shasi Kalivendi
- Biophysics Research Institute and Free Radical Research Center, Medical College of Wisconsin, Milwaukee, WI 5322, USA
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11
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Maita N, Hatakeyama K, Okada K, Hakoshima T. Structural basis of biopterin-induced inhibition of GTP cyclohydrolase I by GFRP, its feedback regulatory protein. J Biol Chem 2004; 279:51534-40. [PMID: 15448133 DOI: 10.1074/jbc.m409440200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
GTP cyclohydrolase I (GTPCHI) is the rate-limiting enzyme involved in the biosynthesis of tetrahydrobiopterin, a key cofactor necessary for nitric oxide synthase and for the hydroxylases that are involved in the production of catecholamines and serotonin. In animals, the GTPCHI feedback regulatory protein (GFRP) binds GTPCHI to mediate feed-forward activation of GTPCHI activity in the presence of phenylalanine, whereas it induces feedback inhibition of enzyme activity in the presence of biopterin. Here, we have reported the crystal structure of the biopterin-induced inhibitory complex of GTPCHI and GFRP and compared it with the previously reported phenylalanine-induced stimulatory complex. The structure reveals five biopterin molecules located at each interface between GTPCHI and GFRP. Induced fitting structural changes by the biopterin binding expand large conformational changes in GTPCHI peptide segments forming the active site, resulting in inhibition of the activity. By locating 3,4-dihydroxy-phenylalanine-responsive dystonia mutations in the complex structure, we found mutations that may possibly disturb the GFRP-mediated regulation of GTPCHI.
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Affiliation(s)
- Nobuo Maita
- Structural Biology Laboratory, Nara Institute of Science and Technology, CREST, Japan Science and Technology Agency, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
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12
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Kolinsky MA, Gross SS. The Mechanism of Potent GTP Cyclohydrolase I Inhibition by 2,4-Diamino-6-hydroxypyrimidine. J Biol Chem 2004; 279:40677-82. [PMID: 15292175 DOI: 10.1074/jbc.m405370200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Inhibition of GTP cyclohydrolase I (GTPCH) has been used as a selective tool to assess the role of de novo synthesis of (6R)-5,6,7,8-tetrahydro-L-biopterin (BH4) in a biological system. Toward this end, 2,4-diamino-6-hydroxypyrimidine (DAHP) has been used as the prototypical GTPCH inhibitor. Using a novel real-time kinetic microplate assay for GTPCH activity and purified prokaryote-expressed recombinant proteins, we show that potent inhibition by DAHP is not the result of a direct interaction with GTPCH. Rather, inhibition by DAHP in phosphate buffer occurs via an indirect mechanism that requires the presence of GTPCH feedback regulatory protein (GFRP). Notably, GFRP was previously discovered as the essential factor that reconstitutes inhibition of pure recombinant GTPCH by the pathway end product BH4. Thus, DAHP inhibits GTPCH by engaging the endogenous feedback inhibitory system. We further demonstrate that L-Phe fully reverses the inhibition of GTPCH by DAHP/GFRP, which is also a feature in common with inhibition by BH4/GFRP. These findings suggest that DAHP is not an indiscriminate inhibitor of GTPCH in biological systems; instead, it is predicted to preferentially attenuate GTPCH activity in cells that most abundantly express GFRP and/or contain the lowest levels of L-Phe.
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Affiliation(s)
- Monica A Kolinsky
- Department of Pharmacology, Weill Medical College of Cornell University, New York, New York 10021, USA
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13
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Gibson CL, La Rosa S, Ohta K, Boyle PH, Leurquin F, Lemaçon A, Suckling CJ. The synthesis of 7-deazaguanines as potential inhibitors of guanosine triphosphate cyclohydrolase I. Tetrahedron 2004. [DOI: 10.1016/j.tet.2003.11.030] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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14
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Hyland K, Kasim S, Egami K, Arnold LA, Jinnah HA. Tetrahydrobiopterin deficiency and dopamine loss in a genetic mouse model of Lesch-Nyhan disease. J Inherit Metab Dis 2004; 27:165-78. [PMID: 15159647 DOI: 10.1023/b:boli.0000028728.93113.4d] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Hypoxanthine-guanine phosphoribosyltransferase (HPRT) is an enzyme that catalyses the conversion of hypoxanthine and guanine into their respective nucleotides. Inherited deficiency of the enzyme is associated with a loss of striatal dopamine in both mouse and man. Although HPRT is not directly involved in the metabolism of dopamine, it contributes to the supply of GTP, which is used in the first and rate-limiting step in the synthesis of tetrahydrobiopterin (BH4). Since BH4 is required as a cofactor for tyrosine hydroxylase in the synthesis of dopamine, any limitation in the supply of GTP could interfere with the synthesis of dopamine. The current studies were designed to address the hypothesis that the reduced striatal dopamine in mice with HPRT deficiency results from reduced availability of BH4. The mutant mice had small reductions in striatal BH4, with normal BH4 levels in other brain regions. Liver BH4 was normal in HPRT-deficient mutant mice, and a phenylalanine challenge test failed to reveal any evidence for impaired hepatic phenylalanine hydroxylase, another BH4-dependent enzyme. Although striatal BH4 content is not normal, supplementation with BH4 or L-dopa failed to correct the striatal dopamine deficiency of the mutant mice, suggesting that BH4 limitation is not responsible for the dopamine loss.
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Affiliation(s)
- K Hyland
- Institute for Metabolic Diseases, Baylor University Medical Center, Dallas, Texas, USA
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15
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16
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Basset G, Quinlivan EP, Ziemak MJ, Diaz De La Garza R, Fischer M, Schiffmann S, Bacher A, Gregory JF, Hanson AD. Folate synthesis in plants: the first step of the pterin branch is mediated by a unique bimodular GTP cyclohydrolase I. Proc Natl Acad Sci U S A 2002; 99:12489-94. [PMID: 12221287 PMCID: PMC129472 DOI: 10.1073/pnas.192278499] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
GTP cyclohydrolase I (GCHI) mediates the first and committing step of the pterin branch of the folate-synthesis pathway. In microorganisms and mammals, GCHI is a homodecamer of approximately 26-kDa subunits. Genomic approaches identified tomato and Arabidopsis cDNAs specifying approximately 50-kDa proteins containing two GCHI-like domains in tandem and indicated that such bimodular proteins occur in other plants. Neither domain of these proteins has a full set of the residues involved in substrate binding and catalysis in other GCHIs. The tomato and Arabidopsis cDNAs nevertheless encode functional enzymes, as shown by complementation of a yeast fol2 mutant and by assaying GCHI activity in extracts of complemented yeast cells. Neither domain expressed separately had GCHI activity. Recombinant tomato GCHI formed dihydroneopterin triphosphate as reaction product, as do other GCHIs, but unlike these enzymes it did not show cooperative behavior and was inhibited by its substrate. Denaturing gel electrophoresis verified that the bimodular GCHI polypeptide is not cleaved in vivo into its component domains, and size-exclusion chromatography indicated that the active enzyme is a dimer. The deduced tomato and Arabidopsis GCHI polypeptides lack overt targeting sequences and thus are presumably cytosolic, in contrast to other plant folate-synthesis enzymes, which are mitochondrial proteins with typical signal peptides. GCHI mRNA and protein are strongly in expressed unripe tomato fruits, implying that fruit folate is made in situ rather than imported. As ripening advances, GCHI expression declines sharply, and folate content drops, suggesting that folate synthesis fails to keep pace with turnover.
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MESH Headings
- Amino Acid Sequence
- Arabidopsis/genetics
- Arabidopsis/growth & development
- Arabidopsis/metabolism
- Base Sequence
- DNA, Complementary/genetics
- DNA, Plant/genetics
- Dimerization
- Enzyme Inhibitors/pharmacology
- Folic Acid/biosynthesis
- GTP Cyclohydrolase/antagonists & inhibitors
- GTP Cyclohydrolase/chemistry
- GTP Cyclohydrolase/genetics
- GTP Cyclohydrolase/metabolism
- Gene Expression Regulation, Plant
- Genes, Plant
- Guanosine Triphosphate/pharmacology
- Solanum lycopersicum/genetics
- Solanum lycopersicum/growth & development
- Solanum lycopersicum/metabolism
- Molecular Sequence Data
- Protein Structure, Tertiary
- Pterins/chemistry
- Pterins/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Plant/genetics
- RNA, Plant/metabolism
- Sequence Homology, Amino Acid
- Species Specificity
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Affiliation(s)
- Gilles Basset
- Horticultural Sciences Department and Food Science and Human Nutrition Department, University of Florida, Gainesville, FL 32611, USA
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Maita N, Okada K, Hatakeyama K, Hakoshima T. Crystal structure of the stimulatory complex of GTP cyclohydrolase I and its feedback regulatory protein GFRP. Proc Natl Acad Sci U S A 2002; 99:1212-7. [PMID: 11818540 PMCID: PMC122169 DOI: 10.1073/pnas.022646999] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2001] [Accepted: 12/04/2001] [Indexed: 11/18/2022] Open
Abstract
In the presence of phenylalanine, GTP cyclohydrolase I feedback regulatory protein (GFRP) forms a stimulatory 360-kDa complex with GTP cyclohydrolase I (GTPCHI), which is the rate-limiting enzyme in the biosynthesis of tetrahydrobiopterin. The crystal structure of the stimulatory complex reveals that the GTPCHI decamer is sandwiched by two GFRP homopentamers. Each GFRP pentamer forms a symmetrical five-membered ring similar to beta-propeller. Five phenylalanine molecules are buried inside each interface between GFRP and GTPCHI, thus enhancing the binding of these proteins. The complex structure suggests that phenylalanine-induced GTPCHI x GFRP complex formation enhances GTPCHI activity by locking the enzyme in the active state.
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Affiliation(s)
- Nobuo Maita
- Department of Molecular Biology, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan
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