Non-heme iron (NHFe) enzymes are ubiquitous in biology and catalyze a wide range of reactions involving dioxygen. These include mono- and dioxygenation, H-atom abstraction for hydroxylation, halogenation and desaturation and electrophilic aromatic attack. The non-heme enzymes can be divided into classes that use a ferrous center to activate dioxygen and classes that use a ferric site to activate substrate for the spin forbidden reaction with dioxygen. The ferrous enzymes include the pterin and ?-ketoglutarate dependent dioxygenases, the Rieske dioxygenases, the extradiol dioxygenases and the anticancer drug Bleomycin. While the natures of the cosubstrate-FeII interactions that activate O2 are not defined, peroxo and high valent oxo intermediates have been trapped in a number of these enzymes and relevant model complexes of these intermediates exist with abiological ligation. The ferric/substrate activating enzymes are the lipoxygenases and the intradiol dioxygenases. Lipoxygenase is thought to activate substrate by H-atom abstraction while for the intradiol dioxygenases substrate activation is thought to occur through direct coordination to the ferric center. No intermediate has been trapped for either enzyme. The non-heme iron enzymes have generally been challenging to study due to their lack of spectral features. The goals of this research project have been to generate new spectroscopic methods and approaches to study the non-heme iron enzymes. These methods are used to experimentally define substrate and cofactor interactions with the iron sites and the natures of the intermediates and their key geometric and electronic contributions to reactivity. Further these experimental results are strongly coupled with density functional theory (DFT) calculations to define structure/function correlations, to understand how the iron site is activated for reaction by substrate or cofactor binding, and to understand their reaction mechanisms on a molecular level. Spectroscopic methods are also being developed to directly probe iron centers in highly covalent porphyrin environments to understand how heme relates to NHFe in oxygen activation and in factors that control reactivity.

Public Health Relevance

The non-heme iron enzymes are involved in antibiotic, collagen and natural product biosynthesis, the synthesis of signaling agents in asthma and atherosclerosis, bioremediation, reactivities related to cancer treatment (hypoxia, DNA repair and cleavage) and their mutations are associated with a range of genetic diseases (phenylketonuria, tyrosinemia, etc.). This research provides definitive insight into NHFe reactivity and the factors that influence this for understanding diseases on a molecular level and to aid in development of new drugs.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Macromolecular Structure and Function A Study Section (MSFA)
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Anderson, Vernon
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Stanford University
Schools of Arts and Sciences
United States
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Srnec, Martin; Wong, Shaun D; Matthews, Megan L et al. (2016) Electronic Structure of the Ferryl Intermediate in the α-Ketoglutarate Dependent Non-Heme Iron Halogenase SyrB2: Contributions to H Atom Abstraction Reactivity. J Am Chem Soc 138:5110-22
Solomon, Edward I; Park, Kiyoung (2016) Structure/function correlations over binuclear non-heme iron active sites. J Biol Inorg Chem 21:575-88
Light, Kenneth M; Yamanaka, Yasuaki; Odaka, Masafumi et al. (2015) Spectroscopic and Computational Studies of Nitrile Hydratase: Insights into Geometric and Electronic Structure and the Mechanism of Amide Synthesis. Chem Sci 6:6280-6294
Kroll, Thomas; Solomon, Edward I; de Groot, Frank M F (2015) Final-State Projection Method in Charge-Transfer Multiplet Calculations: An Analysis of Ti L-Edge Absorption Spectra. J Phys Chem B 119:13852-8
Hong, Seungwoo; Sutherlin, Kyle D; Park, Jiyoung et al. (2014) Crystallographic and spectroscopic characterization and reactivities of a mononuclear non-haem iron(III)-superoxo complex. Nat Commun 5:5440
Pratter, Sarah M; Light, Kenneth M; Solomon, Edward I et al. (2014) The role of chloride in the mechanism of O(2) activation at the mononuclear nonheme Fe(II) center of the halogenase HctB. J Am Chem Soc 136:9385-95
Light, Kenneth M; Hangasky, John A; Knapp, Michael J et al. (2014) First- and second-sphere contributions to Fe(II) site activation by cosubstrate binding in non-heme Fe enzymes. Dalton Trans 43:1505-8
Kang, Mingchao; Light, Kenneth; Ai, Hui-Wang et al. (2014) Evolution of iron(II)-finger peptides by using a bipyridyl amino acid. Chembiochem 15:822-5
Srnec, Martin; Wong, Shaun D; Solomon, Edward I (2014) Excited state potential energy surfaces and their interactions in Fe(IV)=O active sites. Dalton Trans 43:17567-77
Kroll, Thomas; Hadt, Ryan G; Wilson, Samuel A et al. (2014) Resonant inelastic X-ray scattering on ferrous and ferric bis-imidazole porphyrin and cytochrome c: nature and role of the axial methionine-Fe bond. J Am Chem Soc 136:18087-99

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