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)
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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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
Light, Kenneth M; Hangasky, John A; Knapp, Michael J et al. (2013) Spectroscopic studies of the mononuclear non-heme Fe(II) enzyme FIH: second-sphere contributions to reactivity. J Am Chem Soc 135:9665-74
Wilson, Samuel A; Kroll, Thomas; Decreau, Richard A et al. (2013) Iron L-edge X-ray absorption spectroscopy of oxy-picket fence porphyrin: experimental insight into Fe-O2 bonding. J Am Chem Soc 135:1124-36
Liu, Lei V; Hong, Seungwoo; Cho, Jaeheung et al. (2013) Comparison of high-spin and low-spin nonheme Fe(III)-OOH complexes in O-O bond homolysis and H-atom abstraction reactivities. J Am Chem Soc 135:3286-99
Solomon, Edward I; Light, Kenneth M; Liu, Lei V et al. (2013) Geometric and electronic structure contributions to function in non-heme iron enzymes. Acc Chem Res 46:2725-39
Cho, Jaeheung; Kang, Hye Yeon; Liu, Lei V et al. (2013) Mononuclear nickel(II)-superoxo and nickel(III)-peroxo complexes bearing a common macrocyclic TMC ligand. Chem Sci 4:1502-1508
Diebold, Adrienne R; Straganz, Grit D; Solomon, Edward I (2011) Spectroscopic and computational studies of ýý-keto acid binding to Dke1: understanding the role of the facial triad and the reactivity of ýý-diketones. J Am Chem Soc 133:15979-91

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