title: Dynamic regulation of phenylalanine hydroxylase by simulated redox manipulation.
abstract: Recent clinical studies revealed increased phenylalanine levels and phenylalanine to tyrosine ratios in patients suffering from infection, inflammation and general immune activity. These data implicated down-regulation of activity of phenylalanine hydroxylase by oxidative stress upon in vivo immune activation. Though the structural damage of oxidative stress is expected to be comparably small, a structural rationale for this experimental finding was lacking. Hence, we investigated the impact of side chain oxidation at two vicinal cysteine residues on local conformational flexibility in the protein by comparative molecular dynamics simulations. Analysis of backbone dynamics revealed a highly flexible loop region (Tyr138-loop) in proximity to the active center of phenylalanine hydroxylase. We observed elevated loop dynamics in connection with a loop movement towards the active site in the oxidized state, thereby partially blocking access for the substrate phenylalanine. These findings were confirmed by extensive replica exchange molecular dynamics simulations and serve as a first structural explanation for decreased enzyme turnover in situations of oxidative stress.
authors.affiliation: Institute of General, Inorganic and Theoretical Chemistry, and Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innsbruck, Austria.
authors.forename: Julian E
authors.initials: JE
authors.lastname: Fuchs
authors.forename: Roland G
authors.initials: RG
authors.lastname: Huber
authors.forename: Susanne
authors.initials: S
authors.lastname: von Grafenstein
authors.forename: Hannes G
authors.initials: HG
authors.lastname: Wallnoefer
authors.forename: Gudrun M
authors.initials: GM
authors.lastname: Spitzer
authors.forename: Dietmar
authors.initials: D
authors.lastname: Fuchs
authors.forename: Klaus R
authors.initials: KR
authors.lastname: Liedl
mesh_terms: D020134:Catalytic Domain; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010651:Phenylalanine Hydroxylase / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D013379:Substrate Specificity
chemical_list: D010651:Phenylalanine Hydroxylase