title: QM/MM modeling of the hydroxylation of the androstenedione substrate catalyzed by cytochrome P450 aromatase (CYP19A1).
abstract: CYP19A1 aromatase is a member of the Cytochrome P450 family of hemeproteins, and is the enzyme responsible for the final step of the androgens conversion into the corresponding estrogens, via a three-step oxidative process. For this reason, the inhibition of this enzyme plays an important role in the treatment of hormone-dependent breast cancer. The first catalytic subcycle, corresponding to the hydroxilation of androstenedione, has been proposed to occur through a first hydrogen abstraction and a subsequent oxygen rebound step. In present work, we have studied the mechanism of the first catalytic subcycle by means of hybrid quantum mechanics/molecular mechanics methods. The inclusion of the protein flexibility has been achieved by means of Free Energy Perturbation techniques, giving rise to a free energy of activation for the hydrogen abstraction step of 13.5 kcal/mol. The subsequent oxygen rebound step, characterized by a small free energy barrier (1.5 kcal/mol), leads to the hydroxylated products through a highly exergonic reaction. In addition, an analysis of the primary deuterium kinetic isotopic effects, calculated for the hydrogen abstraction step, reveals values (∼10) overpassing the semiclassical limit for the CH, indicating the presence of a substantial tunnel effect. Finally, a decomposition analysis of the interaction energy for the substrate and cofactor in the active site is also discussed. According to our results, the role of the enzymatic environment consists of a transition state stabilization by means of dispersive and polarization effects.
authors.affiliation: Departament de Química Física i Analítica, Universitat Jaume I, Castelló, 12071, Spain.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Viciano
authors.affiliation: Departament de Química Física i Analítica, Universitat Jaume I, Castelló, 12071, Spain.
authors.forename: Raquel
authors.initials: R
authors.lastname: Castillo
authors.affiliation: Departament de Química Física i Analítica, Universitat Jaume I, Castelló, 12071, Spain.
authors.forename: Sergio
authors.initials: S
authors.lastname: Martí
mesh_terms: D000735:Androstenedione / Q000737:chemistry / Q000378:metabolism*; D001141:Aromatase / Q000737:chemistry / Q000378:metabolism*; D001943:Breast Neoplasms / Q000201:enzymology; D020134:Catalytic Domain; D005260:Female; D006801:Humans; D006900:Hydroxylation; D056004:Molecular Dynamics Simulation; D010100:Oxygen / Q000378:metabolism; D011789:Quantum Theory; D013816:Thermodynamics
chemical_list: D000735:Androstenedione; D001141:Aromatase; C561410:CYP19A1 protein, human; D010100:Oxygen
keywords: CYP19A1; androstenedione; aromatase; compound I; cytochrome P450; hydrogen abstraction; quantum mechanics/molecular mechanics