title: Tetrahydrobiopterin shows chaperone activity for tyrosine hydroxylase.
abstract: Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the synthesis of catecholamine neurotransmitters. Primary inherited defects in TH have been associated with l-DOPA responsive and non-responsive dystonia and infantile parkinsonism. In this study, we show that both the cofactor (6R)-l-erythro-5,6,7,8-tetrahydrobiopterin (BH(4)) and the feedback inhibitor and catecholamine product dopamine increase the kinetic stability of human TH isoform 1 in vitro. Activity measurements and synthesis of the enzyme by in vitro transcription-translation revealed a complex regulation by the cofactor including both enzyme inactivation and conformational stabilization. Oral BH(4) supplementation to mice increased TH activity and protein levels in brain extracts, while the Th-mRNA level was not affected. All together our results indicate that the molecular mechanisms for the stabilization are a primary folding-aid effect of BH(4) and a secondary effect by increased synthesis and binding of catecholamine ligands. Our results also establish that orally administered BH(4) crosses the blood-brain barrier and therapeutic regimes based on BH(4) supplementation should thus consider the effect on TH. Furthermore, BH(4) supplementation arises as a putative therapeutic agent in the treatment of brain disorders associated with TH misfolding, such as for the human TH isoform 1 mutation L205P.
authors.affiliation: Department of Pediatrics, University of Zürich, Zürich, Switzerland. beat.thony@kispi.uzh.ch
authors.forename: Beat
authors.initials: B
authors.lastname: Thöny
authors.forename: Ana C
authors.initials: AC
authors.lastname: Calvo
authors.forename: Tanja
authors.initials: T
authors.lastname: Scherer
authors.forename: Randi M
authors.initials: RM
authors.lastname: Svebak
authors.forename: Jan
authors.initials: J
authors.lastname: Haavik
authors.forename: Nenad
authors.initials: N
authors.lastname: Blau
authors.forename: Aurora
authors.initials: A
authors.lastname: Martinez
mesh_terms: D000818:Animals; D001708:Biopterins / Q000008:administration & dosage / Q000031:analogs & derivatives*; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002942:Circular Dichroism / Q000379:methods; D004298:Dopamine / Q000008:administration & dosage / Q000378:metabolism*; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000187:drug effects / Q000502:physiology; D017510:Protein Folding; D014446:Tyrosine 3-Monooxygenase / Q000235:genetics / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D001708:Biopterins; D014446:Tyrosine 3-Monooxygenase; C003402:sapropterin; D004298:Dopamine