Tetrahydrobiopterin (BH4) synthesis, recycling, salvage and regulation (Homo sapiens)

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2, 14, 16, 194, 8, 12, 15, 177336, 7, 13229211, 231820, 25, 261732410, 11cytosolp-S1177-eNOS:CaM:HSP90:p-AKT1:BH4GCHFR BH3.ADPZn2+ sepiapterinFAD Ca2+ PTHPp-PTPS hexamerBH4 CALM1 H+heme Ascorbate radical2xPalmC-MyrG-p-S1177-NOS3 p-S1177-eNOS:CaM:HSP90:p-AKT1:BH2p-S213-SPR FAD Metabolism of nitricoxideFe2+p-T308,S473-AKT1 ATPp-T308,S473-AKT1 PTS heme Ca2+ BH4FMN BH4 p-T308,S473-AKT1 p-SPR dimerSPR H2OGCH1 HSP90AA1 GTPHSP90AA1 PRKG2NADPHATPNADP+GCHFR 2xPalmC-MyrG-p-S1177-NOS3 HSP90AA1 GCHFR pentamerL-PheBH2 PeroxynitriteCa2+ VitCNADP+DHFR dimerFMN DHFR p-S19-PTS GCH1 SPR dimer2GCHFR:GCH1BH2PPPADPCALM1 NADPHPTPS hexamerFe3+FMN Zn2+ NADP+GCH1 decamerDHNTPe-HCOOHFAD CALM1 2xPalmC-MyrG-p-S1177-NOS3 BH4 Zn2+ p-S1177-eNOS:CaM:HSP90:p-AKT1Zn2+ heme 5


Description

Tetrahydrobiopterin (BH4) is an essential co-factor for the aromatic amino acid hydroxylases and glycerol ether monooxygenase and it regulates nitric oxide synthase (NOS) activity. Inherited BH4 deficiency leads to hyperphenylalaninemia, and dopamine and neurotransmitter deficiency in the brain. BH4 maintains enzymatic coupling to L-arginine oxidation to produce NO. Oxidation of BH4 to BH2 results in NOS uncoupling, resulting in superoxide (O2.-) formation rather than NO. Superoxide rapidly reacts with NO to produce peroxynitrite which can further uncouple NOS.
These reactive oxygen species (superoxide and peroxynitrite) can contribute to increased oxidative stress in the endothelium leading to atherosclerosis and hypertension (Thony et al. 2000, Crabtree and Channon 2011,Schulz et al. 2008, Schmidt and Alp 2007). The synthesis, recycling and effects of BH4 are shown here. Three enzymes are required for the de novo biosynthesis of BH4 and two enzymes for the recycling of BH4. View original pathway at:Reactome.

Comments

Reactome-Converter 
Pathway is converted from Reactome ID: 1474151
Reactome-version 
Reactome version: 66
Reactome Author 
Reactome Author: Jassal, Bijay

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Ontology Terms

 

Bibliography

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  1. Fujimoto K, Takahashi SY, Katoh S.; ''Mutational analysis of sites in sepiapterin reductase phosphorylated by Ca2+/calmodulin-dependent protein kinase II.''; PubMed Europe PMC
  2. Crabtree MJ, Channon KM.; ''Synthesis and recycling of tetrahydrobiopterin in endothelial function and vascular disease.''; PubMed Europe PMC
  3. Berka V, Yeh HC, Gao D, Kiran F, Tsai AL.; ''Redox function of tetrahydrobiopterin and effect of L-arginine on oxygen binding in endothelial nitric oxide synthase.''; PubMed Europe PMC
  4. Bürgisser DM, Thöny B, Redweik U, Hunziker P, Heizmann CW, Blau N.; ''Expression and characterization of recombinant human and rat liver 6-pyruvoyl tetrahydropterin synthase. Modified cysteine residues inhibit the enzyme activity.''; PubMed Europe PMC
  5. Pacher P, Beckman JS, Liaudet L.; ''Nitric oxide and peroxynitrite in health and disease.''; PubMed Europe PMC
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  8. Bürgisser DM, Thöny B, Redweik U, Hess D, Heizmann CW, Huber R, Nar H.; ''6-Pyruvoyl tetrahydropterin synthase, an enzyme with a novel type of active site involving both zinc binding and an intersubunit catalytic triad motif; site-directed mutagenesis of the proposed active center, characterization of the metal binding site and modelling of substrate binding.''; PubMed Europe PMC
  9. Vásquez-Vivar J, Martásek P, Whitsett J, Joseph J, Kalyanaraman B.; ''The ratio between tetrahydrobiopterin and oxidized tetrahydrobiopterin analogues controls superoxide release from endothelial nitric oxide synthase: an EPR spin trapping study.''; PubMed Europe PMC
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  13. Baker TA, Milstien S, Katusic ZS.; ''Effect of vitamin C on the availability of tetrahydrobiopterin in human endothelial cells.''; PubMed Europe PMC
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  15. Nar H, Huber R, Heizmann CW, Thöny B, Bürgisser D.; ''Three-dimensional structure of 6-pyruvoyl tetrahydropterin synthase, an enzyme involved in tetrahydrobiopterin biosynthesis.''; PubMed Europe PMC
  16. Schmidt TS, Alp NJ.; ''Mechanisms for the role of tetrahydrobiopterin in endothelial function and vascular disease.''; PubMed Europe PMC
  17. Scherer-Oppliger T, Leimbacher W, Blau N, Thöny B.; ''Serine 19 of human 6-pyruvoyltetrahydropterin synthase is phosphorylated by cGMP protein kinase II.''; PubMed Europe PMC
  18. Sawabe K, Yamamoto K, Harada Y, Ohashi A, Sugawara Y, Matsuoka H, Hasegawa H.; ''Cellular uptake of sepiapterin and push-pull accumulation of tetrahydrobiopterin.''; PubMed Europe PMC
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History

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CompareRevisionActionTimeUserComment
101712view14:51, 1 November 2018DeSlOntology Term : 'tetrahydrobiopterin metabolic pathway' added !
101372view11:26, 1 November 2018ReactomeTeamreactome version 66
100910view21:01, 31 October 2018ReactomeTeamreactome version 65
100451view19:35, 31 October 2018ReactomeTeamreactome version 64
100274view16:57, 31 October 2018ReactomeTeamNew pathway

External references

DataNodes

View all...
NameTypeDatabase referenceComment
2GCHFR:GCH1ComplexR-HSA-1474149 (Reactome)
2xPalmC-MyrG-p-S1177-NOS3 ProteinP29474 (Uniprot-TrEMBL)
ADPMetaboliteCHEBI:16761 (ChEBI)
ATPMetaboliteCHEBI:15422 (ChEBI)
Ascorbate radicalMetaboliteCHEBI:59513 (ChEBI)
BH2 MetaboliteCHEBI:15375 (ChEBI)
BH2MetaboliteCHEBI:15375 (ChEBI)
BH3.MetaboliteCHEBI:62772 (ChEBI)
BH4 MetaboliteCHEBI:15372 (ChEBI)
BH4MetaboliteCHEBI:15372 (ChEBI)
CALM1 ProteinP0DP23 (Uniprot-TrEMBL)
Ca2+ MetaboliteCHEBI:29108 (ChEBI)
DHFR ProteinP00374 (Uniprot-TrEMBL)
DHFR dimerComplexR-HSA-1497822 (Reactome)
DHNTPMetaboliteCHEBI:18372 (ChEBI)
FAD MetaboliteCHEBI:16238 (ChEBI)
FMN MetaboliteCHEBI:17621 (ChEBI)
Fe2+MetaboliteCHEBI:18248 (ChEBI)
Fe3+MetaboliteCHEBI:29034 (ChEBI)
GCH1 ProteinP30793 (Uniprot-TrEMBL)
GCH1 decamerComplexR-HSA-1474144 (Reactome)
GCHFR ProteinP30047 (Uniprot-TrEMBL)
GCHFR pentamerComplexR-HSA-1474155 (Reactome)
GTPMetaboliteCHEBI:15996 (ChEBI)
H+MetaboliteCHEBI:15378 (ChEBI)
H2OMetaboliteCHEBI:15377 (ChEBI)
HCOOHMetaboliteCHEBI:30751 (ChEBI)
HSP90AA1 ProteinP07900 (Uniprot-TrEMBL)
L-PheMetaboliteCHEBI:58095 (ChEBI)
Metabolism of nitric oxidePathwayR-HSA-202131 (Reactome) Nitric oxide (NO), a multifunctional second messenger, is implicated in physiological functions in mammals that range from immune response and potentiation of synaptic transmission to dilation of blood vessels and muscle relaxation. NO is a highly active molecule that diffuses across cell membranes and cannot be stored inside the producing cell. Its signaling capacity must be controlled at the levels of biosynthesis and local availability. Indeed, NO production by NO synthases is under complex and tight control, being regulated at transcriptional and translational levels, through co- and posttranslational modifications, and by subcellular localization. NO is synthesized from L-arginine by a family of nitric oxide synthases (NOS). Three NOS isoforms have been characterized: neuronal NOS (nNOS, NOS1) primarily found in neuronal tissue and skeletal muscle; inducible NOS (iNOS, NOS2) originally isolated from macrophages and later discovered in many other cells types; and endothelial NOS (eNOS, NOS3) present in vascular endothelial cells, cardiac myocytes, and in blood platelets. The enzymatic activity of all three isoforms is dependent on calmodulin, which binds to nNOS and eNOS at elevated intracellular calcium levels, while it is tightly associated with iNOS even at basal calcium levels. As a result, the enzymatic activity of nNOS and eNOS is modulated by changes in intracellular calcium levels, leading to transient NO production, while iNOS continuously releases NO independent of fluctuations in intracellular calcium levels and is mainly regulated at the gene expression level (Pacher et al. 2007).

The NOS enzymes share a common basic structural organization and requirement for substrate cofactors for enzymatic activity. A central calmodulin-binding motif separates an oxygenase (NH2-terminal) domain from a reductase (COOH-terminal) domain. Binding sites for cofactors NADPH, FAD, and FMN are located within the reductase domain, while binding sites for tetrahydrobiopterin (BH4) and heme are located within the oxygenase domain. Once calmodulin binds, it facilitates electron transfer from the cofactors in the reductase domain to heme enabling nitric oxide production. Both nNOS and eNOS contain an additional insert (40-50 amino acids) in the middle of the FMN-binding subdomain that serves as autoinhibitory loop, destabilizing calmodulin binding at low calcium levels and inhibiting electron transfer from FMN to the heme in the absence of calmodulin. iNOS does not contain this insert.

Because NOS enzymatic activity is modulated by the presence of its substrates and cofactors within the cell, under certain conditions, NOS may generate superoxide instead of NO, a process referred to as uncoupling (uncoupling of NADPH oxidation and NO synthesis).

The molecular details of eNOS function are annotated here.

NADP+MetaboliteCHEBI:18009 (ChEBI)
NADPHMetaboliteCHEBI:16474 (ChEBI)
PPPMetaboliteCHEBI:15266 (ChEBI)
PRKG2ProteinQ13237 (Uniprot-TrEMBL)
PTHPMetaboliteCHEBI:17804 (ChEBI)
PTPS hexamerComplexR-HSA-1497879 (Reactome)
PTS ProteinQ03393 (Uniprot-TrEMBL)
PeroxynitriteMetaboliteCHEBI:25941 (ChEBI)
SPR ProteinP35270 (Uniprot-TrEMBL)
SPR dimerComplexR-HSA-1497791 (Reactome)
VitCMetaboliteCHEBI:29073 (ChEBI)
Zn2+ MetaboliteCHEBI:29105 (ChEBI)
e-MetaboliteCHEBI:10545 (ChEBI)
heme MetaboliteCHEBI:17627 (ChEBI)
p-PTPS hexamerComplexR-HSA-1475058 (Reactome)
p-S1177-eNOS:CaM:HSP90:p-AKT1:BH2ComplexR-HSA-1497889 (Reactome)
p-S1177-eNOS:CaM:HSP90:p-AKT1:BH4ComplexR-HSA-1497830 (Reactome)
p-S1177-eNOS:CaM:HSP90:p-AKT1ComplexR-HSA-202121 (Reactome)
p-S19-PTS ProteinQ03393 (Uniprot-TrEMBL)
p-S213-SPR ProteinP35270 (Uniprot-TrEMBL)
p-SPR dimerComplexR-HSA-1497817 (Reactome)
p-T308,S473-AKT1 ProteinP31749 (Uniprot-TrEMBL)
sepiapterinMetaboliteCHEBI:16095 (ChEBI)

Annotated Interactions

View all...
SourceTargetTypeDatabase referenceComment
2GCHFR:GCH1ArrowR-HSA-1474158 (Reactome)
2GCHFR:GCH1TBarR-HSA-1474146 (Reactome)
ADPArrowR-HSA-1475422 (Reactome)
ADPArrowR-HSA-1497853 (Reactome)
ATPR-HSA-1475422 (Reactome)
ATPR-HSA-1497853 (Reactome)
Ascorbate radicalArrowR-HSA-1497855 (Reactome)
BH2ArrowR-HSA-1497863 (Reactome)
BH2ArrowR-HSA-1497869 (Reactome)
BH2R-HSA-1497794 (Reactome)
BH2R-HSA-1497796 (Reactome)
BH3.ArrowR-HSA-1497824 (Reactome)
BH3.ArrowR-HSA-1497866 (Reactome)
BH3.R-HSA-1497855 (Reactome)
BH3.R-HSA-1497863 (Reactome)
BH3.R-HSA-1497883 (Reactome)
BH4ArrowR-HSA-1475414 (Reactome)
BH4ArrowR-HSA-1497794 (Reactome)
BH4ArrowR-HSA-1497796 (Reactome)
BH4ArrowR-HSA-1497855 (Reactome)
BH4ArrowR-HSA-1497883 (Reactome)
BH4R-HSA-1497784 (Reactome)
BH4R-HSA-1497824 (Reactome)
BH4R-HSA-1497866 (Reactome)
BH4TBarR-HSA-1474146 (Reactome)
DHFR dimermim-catalysisR-HSA-1497794 (Reactome)
DHNTPArrowR-HSA-1474146 (Reactome)
DHNTPR-HSA-1474184 (Reactome)
Fe2+R-HSA-1497883 (Reactome)
Fe3+ArrowR-HSA-1497883 (Reactome)
GCH1 decamerR-HSA-1474158 (Reactome)
GCH1 decamermim-catalysisR-HSA-1474146 (Reactome)
GCHFR pentamerR-HSA-1474158 (Reactome)
GTPR-HSA-1474146 (Reactome)
H+R-HSA-1497794 (Reactome)
H+R-HSA-1497869 (Reactome)
H2OR-HSA-1474146 (Reactome)
HCOOHArrowR-HSA-1474146 (Reactome)
L-PheArrowR-HSA-1474146 (Reactome)
NADP+ArrowR-HSA-1475414 (Reactome)
NADP+ArrowR-HSA-1497794 (Reactome)
NADP+ArrowR-HSA-1497869 (Reactome)
NADPHR-HSA-1475414 (Reactome)
NADPHR-HSA-1497794 (Reactome)
NADPHR-HSA-1497869 (Reactome)
PPPArrowR-HSA-1474184 (Reactome)
PRKG2mim-catalysisR-HSA-1475422 (Reactome)
PRKG2mim-catalysisR-HSA-1497853 (Reactome)
PTHPArrowR-HSA-1474184 (Reactome)
PTHPR-HSA-1475414 (Reactome)
PTPS hexamerR-HSA-1475422 (Reactome)
PeroxynitriteR-HSA-1497866 (Reactome)
R-HSA-1474146 (Reactome) The first and rate-limiting enzyme in tetrahydrobiopterin de novo biosynthesis is GTP cyclohydrolase I (GCH1, GTPCHI). Three different isoforms are produced but only isoform 1 is functionally active (Gütlich et al. 1994). GCH1 is functional as a homodecamer. First, a monomer of GCH1 forms a dimer. Then five dimers arrange into a ring-like structure to form the homodecamer (Nar et al. 1995).
R-HSA-1474158 (Reactome) High levels of the end product, BH4, negatively regulates GCH1. It does this via GTP cyclohydrolase 1 feedback regulatory protein (GCHFR). BH4-dependant GCHFR in the form of a homopentamer complexes with the decameric GCH1 enzyme in the ratio 2:1 to inactivate it. L-phenylalanine reverses this inhibition. These regulatory steps control the biosynthesis of BH4. (Swick & Kapatos 2006, Chavan et al. 2006, Harada et al. 1993).
R-HSA-1474184 (Reactome) 6-pyruvoyl tetrahydrobiopterin synthase (PTPS) (Takikawa et al. 1986) catalyses the second step in BH4 biosynthesis, the dephosphorylation of DHNTP to 6-pyruvoyl-tetrahydropterin (PTHP). PTPS is believed to function as a homohexamer (Nar et al. 1994, Bürgisser et al. 1994) and has a requirement for Zn2+ (one Zn2+ ion bound per subunit) and Mg2+ ions for activity (Bürgisser et al. 1995). The phosphorylation of Ser-19 is an essential modification for enzyme activity (Scherer-Oppliger et al. 1999).
R-HSA-1475414 (Reactome) Sepiapterin reductase (SPR) (Ichinose et al. 1991) reduces DHNTP to tetrahydrobiopterin (BH4).
R-HSA-1475422 (Reactome) 6-pyruvoyl tetrahydrobiopterin synthase (PTPS) requires phosphorylation on Ser-19 for enzyme activity (Scherer-Oppliger et al. 1999).
R-HSA-1497784 (Reactome) The cofactor tetrahydrobiopterin (BH4) ensures endothelial nitric oxide synthase (eNOS) couples electron transfer to L-arginine oxidation (Berka et al. 2004). During catalysis, electrons derived from NADPH transfer to the flavins FAD and FMN in the reductase domain of eNOS and then on to the ferric heme in the oxygenase domain of eNOS. BH4 can donate an electron to intermediates in this electron transfer and is oxidised in the process, forming the BH3 radical. This radical can be reduced back to BH4 by iron, completing the cycle and forming ferrous iron again. Heme reduction enables O2 binding and L-arginine oxidation to occur within the oxygenase domain (Stuehr et al. 2009).
R-HSA-1497794 (Reactome) In the second salvage step, dihydrofolate reductase (DHFR) can regenerate BH4 from BH2, a process which increases the BH4:BH2 ratio providing BH4 for coupled eNOS production of NO. In mice cell lines, DHFR inhibition or knockdown diminishes the BH4:BH2 ratio and exacerbates eNOS uncoupling (Crabtree et al. 2009).
R-HSA-1497796 (Reactome) The oxidation product of BH4, 7,8-dihydrobiopterin (BH2), can compete with BH4 for binding to eNOS. This can lead to the uncoupling of eNOS and can result in the formation of reactive oxygen species (Vasquez-Vivar et al. 2002).
R-HSA-1497824 (Reactome) BH4 donates an electron to the eNOS catalytic cycle and is oxidised to the BH3 radical (BH3.-) (Berka et al. 2004).
R-HSA-1497853 (Reactome) To become active, sepiapterin reductase (SPR) must first be phosphorylated (serine 213 in humans) by Ca2+/calmodulin-dependent protein kinase II (Fujimoto et al. 2002, Katoh et al. 1994).
R-HSA-1497855 (Reactome) Ascorbate (vitamin C) can reduce the BH3 radical back to BH4, thereby maintaining BH4 levels (Baker et al. 2001, Patel et al. 2002, Kuzkaya et al. 2003).
R-HSA-1497863 (Reactome) BH4 oxidation results in the radical BH3. which decays to 7,8-dihydrobiopterin (BH2) (Milstien & Katusic, 1999).
R-HSA-1497866 (Reactome) Peroxynitrite can oxidise BH4 to the BH3 radical, further reducing BH4 availability to couple eNOS activity and compounding the production of superoxide through uncoupled eNOS activity (Kuzkaya et al. 2003).
R-HSA-1497869 (Reactome) In the first of two salvage steps to maintain BH4 levels in the cell, sepiapterin is taken up by the cell and reduced by sepiapterin reductase (SRP) to form BH2 (Sawabe et al. 2008).
R-HSA-1497883 (Reactome) Heme iron from the oxygenase domain of eNOS can reduce the BH3 radical back to BH4, with itself being oxidised from the ferrous (Fe2+) back to the ferric (Fe3+) form (Berka et al. 2004).
SPR dimerR-HSA-1497853 (Reactome)
VitCR-HSA-1497855 (Reactome)
e-ArrowR-HSA-1497824 (Reactome)
p-PTPS hexamerArrowR-HSA-1475422 (Reactome)
p-PTPS hexamermim-catalysisR-HSA-1474184 (Reactome)
p-S1177-eNOS:CaM:HSP90:p-AKT1:BH2ArrowR-HSA-1497796 (Reactome)
p-S1177-eNOS:CaM:HSP90:p-AKT1:BH4ArrowR-HSA-1497784 (Reactome)
p-S1177-eNOS:CaM:HSP90:p-AKT1:BH4R-HSA-1497796 (Reactome)
p-S1177-eNOS:CaM:HSP90:p-AKT1R-HSA-1497784 (Reactome)
p-SPR dimerArrowR-HSA-1497853 (Reactome)
p-SPR dimermim-catalysisR-HSA-1475414 (Reactome)
p-SPR dimermim-catalysisR-HSA-1497869 (Reactome)
sepiapterinR-HSA-1497869 (Reactome)
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