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Coupled electron transfer and proton hopping in the final step of CYP19-catalyzed androgen aromatization.

ABSTRACT: Aromatase (CYP19) catalyzes the terminal step in estrogen biosynthesis, which requires three separate oxidation reactions, culminating in an enigmatic aromatization that converts an androgen to an estrogen. A stable ferric peroxo (Fe(3+)O(2)(2-)) intermediate is seen by electron paramagnetic resonance, but its role in this complex reaction remains controversial. Combining molecular dynamics simulation and hybrid quantum mechanics/molecular mechanics, we show that ferric peroxo addition to the 19-aldehyde initiates the reaction. Stepwise cleavage of the C10-C19 and O-O bonds of the peroxohemiacetal extrudes formate and yields Compound II, which in turn desaturates the steroid through successive abstraction of the 1?-hydrogen atom and deprotonation of the 2?-position. Throughout the transformation, a proton is cyclically relayed between D309 and the substrate to stabilize reaction intermediates. This mechanism invokes novel oxygen intermediates and provides a unifying interpretation of past experimental mechanistic studies.

SUBMITTER: Sen K

PROVIDER: S-EPMC3326664 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature

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Coupled electron transfer and proton hopping in the final step of CYP19-catalyzed androgen aromatization.

Sen Kakali K Hackett John C JC

Biochemistry 20120327 14

Aromatase (CYP19) catalyzes the terminal step in estrogen biosynthesis, which requires three separate oxidation reactions, culminating in an enigmatic aromatization that converts an androgen to an estrogen. A stable ferric peroxo (Fe(3+)O(2)(2-)) intermediate is seen by electron paramagnetic resonance, but its role in this complex reaction remains controversial. Combining molecular dynamics simulation and hybrid quantum mechanics/molecular mechanics, we show that ferric peroxo addition to the 19 ...[more]

PMID: 22439696

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Project description:Designing molecular platforms for controlling proton and electron movement in artificial photosynthetic systems is crucial to efficient catalysis and solar energy conversion. The transfer of both protons and electrons during a reaction is known as proton-coupled electron transfer (PCET) and is used by nature in myriad ways to provide low overpotential pathways for redox reactions and redox leveling, as well as to generate bioenergetic proton currents. Herein, we describe theoretical and electrochemical studies of a series of bioinspired benzimidazole-phenol (BIP) derivatives and a series of dibenzimidazole-phenol (BI2P) analogs with each series bearing the same set of terminal proton-accepting (TPA) groups. The set of TPAs spans more than 6 pK a units. These compounds have been designed to explore the role of the bridging benzimidazole(s) in a one-electron oxidation process coupled to intramolecular proton translocation across either two (the BIP series) or three (the BI2P series) acid/base sites. These molecular constructs feature an electrochemically active phenol connected to the TPA group through a benzimidazole-based bridge, which together with the phenol and TPA group form a covalent framework supporting a Grotthuss-type hydrogen-bonded network. Infrared spectroelectrochemistry demonstrates that upon oxidation of the phenol, protons translocate across this well-defined hydrogen-bonded network to a TPA group. The experimental data show the benzimidazole bridges are non-innocent participants in the PCET process in that the addition of each benzimidazole unit lowers the redox potential of the phenoxyl radical/phenol couple by 60 mV, regardless of the nature of the TPA group. Using a series of hypothetical thermodynamic steps, density functional theory calculations correctly predicted the dependence of the redox potential of the phenoxyl radical/phenol couple on the nature of the final protonated species and provided insight into the thermodynamic role of dibenzimidazole units in the PCET process. This information is crucial for developing molecular "dry proton wires" with these moieties, which can transfer protons via a Grotthuss-type mechanism over long distances without the intervention of water molecules.

Dataset Information

Coupled electron transfer and proton hopping in the final step of CYP19-catalyzed androgen aromatization.

Publications

Coupled electron transfer and proton hopping in the final step of CYP19-catalyzed androgen aromatization.

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