title: Tetrahydrobiopterin binding to aromatic amino acid hydroxylases. Ligand recognition and specificity.
abstract: The three aromatic amino acid hydroxylases (phenylalanine, tyrosine, and tryptophan hydroxylase) and nitric oxide synthase (NOS) all utilize (6R)-l-erythro-5,6,7,8-tetrahydrobiopterin (BH(4)) as cofactor. The pterin binding site in the three hydroxylases is well conserved and different from the binding site in NOS. The structures of phenylalanine hydroxylase (PAH) and of NOS in complex with BH(4) are still the only crystal structures available for the reduced cofactor-enzyme complexes. We have studied the enzyme-bound and free conformations of BH(4) by NMR spectroscopy and molecular docking into the active site of the three hydroxylases, using endothelial NOS as a comparative probe. We have found that the dihydroxypropyl side chain of BH(4) adopts different conformations depending on which hydroxylase it interacts with. All the bound conformations are different from that of BH(4) free in solution at neutral pH. The different bound conformations appear to result from specific interactions with nonconserved amino acids at the BH(4) binding sites of the hydroxylases, notably the stretch 248-251 (numeration in PAH) and the residue corresponding to Ala322 in PAH, i.e., Ser in TH and Ala in TPH. On the basis of analysis of molecular interaction fields, we discuss the selectivity determinants for each hydroxylase and explain the high-affinity inhibitory effect of 7-tetrahydrobiopterin specifically for PAH.
authors.affiliation: Department of Biomedicine, University of Bergen, Jonas Lies vei 91, 5009-Bergen, Norway.
authors.forename: Knut
authors.initials: K
authors.lastname: Teigen
authors.forename: Khanh K
authors.initials: KK
authors.lastname: Dao
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: McKinney
authors.forename: Antonius C F
authors.initials: AC
authors.lastname: Gorren
authors.forename: Bernd
authors.initials: B
authors.lastname: Mayer
authors.forename: Nils Age
authors.initials: NA
authors.lastname: Frøystein
authors.forename: Jan
authors.initials: J
authors.lastname: Haavik
authors.forename: Aurora
authors.initials: A
authors.lastname: Martínez
mesh_terms: D000595:Amino Acid Sequence; D001708:Biopterins / Q000031:analogs & derivatives* / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D015394:Molecular Structure; D019001:Nitric Oxide Synthase / Q000737:chemistry; D052250:Nitric Oxide Synthase Type III; D010651:Phenylalanine Hydroxylase / Q000737:chemistry*; D011485:Protein Binding; D013237:Stereoisomerism; D013379:Substrate Specificity; D014365:Tryptophan Hydroxylase / Q000737:chemistry*; D014446:Tyrosine 3-Monooxygenase / Q000737:chemistry*
chemical_list: D008024:Ligands; D001708:Biopterins; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; D010651:Phenylalanine Hydroxylase; D014446:Tyrosine 3-Monooxygenase; D014365:Tryptophan Hydroxylase; C003402:sapropterin