title: Empirical Valence Bond Simulations of the Hydride-Transfer Step in the Monoamine Oxidase A Catalyzed Metabolism of Noradrenaline.
abstract: Monoamine oxidases (MAOs) A and B are flavoenzymes responsible for the metabolism of biogenic amines, such as dopamine, serotonin, and noradrenaline (NA), which is why they have been extensively implicated in the etiology and course of various neurodegenerative disorders and, accordingly, used as primary pharmacological targets to treat these debilitating cognitive diseases. The precise chemical mechanism through which MAOs regulate the amine concentration, which is vital for the development of novel inhibitors, is still not unambiguously determined in the literature. In this work, we present atomistic empirical valence bond simulations of the rate-limiting step of the MAO-A-catalyzed NA (norepinephrine) degradation, involving hydride transfer from the substrate α-methylene group to the flavin moiety of the flavin adenine dinucleotide prosthetic group, employing the full dimensionality and thermal fluctuations of the hydrated enzyme, with extensive configurational sampling. We show that MAO-A lowers the free energy of activation by 14.3 kcal mol-1relative to that of the same reaction in aqueous solution, whereas the calculated activation free energy of ΔG‡= 20.3 ± 1.6 kcal mol-1is found to be in reasonable agreement with the correlated experimental value of 16.5 kcal mol-1. The results presented here strongly support the fact that both MAO-A and MAO-B isoforms function by the same hydride-transfer mechanism. We also considered a few point mutations of the "aromatic cage" tyrosine residue (Tyr444Phe, Tyr444Leu, Tyr444Trp, Tyr444His, and Tyr444Glu), and the calculated changes in the reaction barriers are in agreement with the experimental values, thus providing further support to the proposed mechanism.
authors.affiliation: Department of Physical and Organic Chemistry, Jožef Stefan Institute , Jamova cesta 39, SI-1000 Ljubljana, Slovenia.
authors.forename: Matic
authors.initials: M
authors.lastname: Poberžnik
authors.affiliation: Department of Cell and Molecular Biology, Uppsala Biomedical Centre , Husargatan 3, S-75124 Uppsala, Sweden.
authors.forename: Miha
authors.initials: M
authors.lastname: Purg
authors.affiliation: Laboratory for Biocomputing and Bioinformatics, National Institute of Chemistry , Hajdrihova ulica 19, SI-1000 Ljubljana, Slovenia.
authors.forename: Matej
authors.initials: M
authors.lastname: Repič
authors.affiliation: Laboratory for Biocomputing and Bioinformatics, National Institute of Chemistry , Hajdrihova ulica 19, SI-1000 Ljubljana, Slovenia.
authors.forename: Janez
authors.initials: J
authors.lastname: Mavri
authors.affiliation: Computational Organic Chemistry and Biochemistry Group, Ruđer Bošković Institute , Bijenička cesta 54, HR-10000 Zagreb, Croatia.
authors.forename: Robert
authors.initials: R
authors.lastname: Vianello
mesh_terms: D055162:Biocatalysis; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D008995:Monoamine Oxidase / Q000737:chemistry / Q000378:metabolism*; D009638:Norepinephrine / Q000737:chemistry / Q000378:metabolism*; D011789:Quantum Theory
chemical_list: D008995:Monoamine Oxidase; C579458:monoamine oxidase A, human; D009638:Norepinephrine