High-Energy-Resolution Fluorescence-Detected X-ray Absorption of the Q Intermediate of Soluble Methane Monooxygenase

Rebeca G. Castillo, Rahul Banerjee, Caleb J. Allpress, Gregory T. Rohde, Eckhard Bill, Larry Que, John D Lipscomb, Serena DeBeer

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

Kα high-energy-resolution fluorescence detected X-ray absorption spectroscopy (HERFD XAS) provides a powerful tool for overcoming the limitations of conventional XAS to identify the electronic structure and coordination environment of metalloprotein active sites. Herein, Fe Kα HERFD XAS is applied to the diiron active site of soluble methane monooxygenase (sMMO) and to a series of high-valent diiron model complexes, including diamond-core [FeIV 2(μ-O)2(L)2](ClO4)4] (3) and open-core [(O=FeIV-O-FeIV(OH)(L)2](ClO4)3 (4) models (where, L = tris(3,5-dimethyl-4-methoxypyridyl-2-methyl)amine) (TPA∗)). Pronounced differences in the HERFD XAS pre-edge energies and intensities are observed for the open versus closed Fe2O2 cores in the model compounds. These differences are reproduced by time-dependent density functional theory (TDDFT) calculations and allow for the pre-edge energies and intensity to be directly correlated with the local active site geometric and electronic structure. A comparison of the model complex HERFD XAS data to that of MMOHQ (the key intermediate in methane oxidation) is supportive of an open-core structure. Specifically, the large pre-edge area observed for MMOHQ may be rationalized by invoking an open-core structure with a terminal FeIV=O motif, though further modulations of the core structure due to the protein environment cannot be ruled out. The present study thus motivates the need for additional experimental and theoretical studies to unambiguously assess the active site conformation of MMOHQ.

Original languageEnglish (US)
Pages (from-to)18024-18033
Number of pages10
JournalJournal of the American Chemical Society
Volume139
Issue number49
DOIs
StatePublished - Dec 13 2017

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methane monooxygenase
X-Ray Absorption Spectroscopy
X ray absorption spectroscopy
X ray absorption
Catalytic Domain
Methane
Fluorescence
X-Rays
Electronic structure
Metalloproteins
Diamond
Amines
Density functional theory
Conformations
Diamonds
Theoretical Models
Modulation
Proteins
Oxidation

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High-Energy-Resolution Fluorescence-Detected X-ray Absorption of the Q Intermediate of Soluble Methane Monooxygenase. / Castillo, Rebeca G.; Banerjee, Rahul; Allpress, Caleb J.; Rohde, Gregory T.; Bill, Eckhard; Que, Larry; Lipscomb, John D; DeBeer, Serena.

In: Journal of the American Chemical Society, Vol. 139, No. 49, 13.12.2017, p. 18024-18033.

Research output: Contribution to journalArticle

Castillo, Rebeca G. ; Banerjee, Rahul ; Allpress, Caleb J. ; Rohde, Gregory T. ; Bill, Eckhard ; Que, Larry ; Lipscomb, John D ; DeBeer, Serena. / High-Energy-Resolution Fluorescence-Detected X-ray Absorption of the Q Intermediate of Soluble Methane Monooxygenase. In: Journal of the American Chemical Society. 2017 ; Vol. 139, No. 49. pp. 18024-18033.
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abstract = "Kα high-energy-resolution fluorescence detected X-ray absorption spectroscopy (HERFD XAS) provides a powerful tool for overcoming the limitations of conventional XAS to identify the electronic structure and coordination environment of metalloprotein active sites. Herein, Fe Kα HERFD XAS is applied to the diiron active site of soluble methane monooxygenase (sMMO) and to a series of high-valent diiron model complexes, including diamond-core [FeIV 2(μ-O)2(L)2](ClO4)4] (3) and open-core [(O=FeIV-O-FeIV(OH)(L)2](ClO4)3 (4) models (where, L = tris(3,5-dimethyl-4-methoxypyridyl-2-methyl)amine) (TPA∗)). Pronounced differences in the HERFD XAS pre-edge energies and intensities are observed for the open versus closed Fe2O2 cores in the model compounds. These differences are reproduced by time-dependent density functional theory (TDDFT) calculations and allow for the pre-edge energies and intensity to be directly correlated with the local active site geometric and electronic structure. A comparison of the model complex HERFD XAS data to that of MMOHQ (the key intermediate in methane oxidation) is supportive of an open-core structure. Specifically, the large pre-edge area observed for MMOHQ may be rationalized by invoking an open-core structure with a terminal FeIV=O motif, though further modulations of the core structure due to the protein environment cannot be ruled out. The present study thus motivates the need for additional experimental and theoretical studies to unambiguously assess the active site conformation of MMOHQ.",
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AU - Rohde, Gregory T.

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AU - Que, Larry

AU - Lipscomb, John D

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