背景介绍
This gene encodes a member of the GTP cyclohydrolase family. The encoded protein is the first and rate-limiting enzyme in tetrahydrobiopterin (BH4) biosynthesis, catalyzing the conversion of GTP into 7,8-dihydroneopterin triphosphate. BH4 is an essential cofactor required by aromatic amino acid hydroxylases as well as nitric oxide synthases. Mutations in this gene are associated with malignant hyperphenylalaninemia and dopa-responsive dystonia. Several alternatively spliced transcript variants encoding different isoforms have been described; however, not all variants give rise to a functional enzyme. [provided by RefSeq, Jul 2008],
功能
catalytic activity:GTP + H(2)O = formate + 2-amino-4-hydroxy-6-(erythro-1,2,3-trihydroxypropyl)-dihydropteridine triphosphate.,disease:Defects in GCH1 are the cause of dystonia type 5 (DYT5) [MIM:128230]; also known as progressive dystonia with diurnal fluctuation, autosomal dominant Segawa syndrome or dystonia-parkinsonism with diurnal fluctuation. DYT5 is a DOPA-responsive dystonia. Dystonia is defined by the presence of sustained involuntary muscle contractions, often leading to abnormal postures. DYT5 typically presents in childhood with walking problems due to dystonia of the lower limbs and worsening of the dystonia towards the evening. It is characterized by postural and motor disturbances showing marked diurnal fluctuation. Torsion of the trunk is unusual. Symptoms are alleviated after sleep and aggravated by fatigue and excercise. There is a favorable response to L-DOPA without side effects.,disease:Defects in GCH1 are the cause of GTP cyclohydrolase 1 deficiency (GCH1D) [MIM:233910]; also known as atypical severe phenylketonuria due to GTP cyclohydrolase I deficiency;. GCH1D is one of the causes of malignant hyperphenylalaninemia due to tetrahydrobiopterin deficiency. It is also responsible for defective neurotransmission due to depletion of the neurotransmitters dopamine and serotonin. The principal symptoms include: psychomotor retardation, tonicity disorders, convulsions, drowsiness, irritability, abnormal movements, hyperthermia, hypersalivation, and difficulty swallowing. Some patients may present a phenotype of intermediate severity between severe hyperphenylalaninemia and mild dystonia type 5 (dystonia-parkinsonism with diurnal fluctuation). In this intermediate phenotype, there is marked motor delay, but no mental retardation and only minimal, if any, hyperphenylalaninemia.,enzyme regulation:GTP shows a positive allosteric effect, and tetrahydrobiopterin inhibits the enzyme activity. Zinc is required for catalytic activity. Inhibited by Mg(2+).,function:Positively regulates nitric oxide synthesis in umbilical vein endothelial cells (HUVECs). May be involved in dopamine synthesis. May modify pain sensitivity and persistence. Isoform GCH-1 is the functional enzyme, the potential function of the enzymatically inactive isoforms remains unknown.,induction:Up-regulated by interferon gamma (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), interleukin 1-beta (IL-beta), lipopolysaccharide (LPS) and phenylalanine, and down-regulated by dibutyryl-cAMP, iloprost and 8-bromo-cGMP in HUVEC cells. Up-regulation of GCH1 expression, in turn, stimulates production of tetrahydrobiopterin, with subsequent elevation of endothelial nitric oxide synthase activity. Cytokine-induced GCH1 up-regulation in HUVECs in response to TNF-alpha and IFN-gamma involves cooperative activation of both the NF-kappa-B and JAK2/STAT pathways. Also up-regulated by hydrogen peroxide in human aorta endothelial cells (HAECs).,online information:Db of mutations causing tetrahydrobiopterin deficiencies,pathway:Cofactor biosynthesis; dihydroneopterin triphosphate biosynthesis; 2-amino-4-hydroxy-6-(erythro-1,2,3-trihydroxypropyl)-dihydropteridine triphosphate from GTP: step 1/1.,PTM:Phosphorylated by casein kinase II at Ser-81 in HAECs during oscillatory shear stress; phosphorylation at Ser-81 results in increased enzyme activity.,similarity:Belongs to the GTP cyclohydrolase I family.,subunit:Toroid-shaped homodecamer, composed of a dimer of pentamers. The inactive isoforms also form decamers and may possibly be incorporated into GCH1 heterodecamers, decreasing enzyme stability and activity. Interacts with AHSA1 and GCHFR/GFRP.,tissue specificity:In epidermis, expressed predominantly in basal undifferentiated keratinocytes and in some but not all melanocytes (at protein level).,
