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Title: Peroxide Activation for Electrophilic Reactivity by the Binuclear Non-heme Iron Enzyme AurF

Abstract

Binuclear non-heme iron enzymes activate O 2 for diverse chemistries that include oxygenation of organic substrates and hydrogen atom abstraction. This process often involves the formation of peroxo-bridged biferric intermediates, only some of which can perform electrophilic reactions. To elucidate the geometric and electronic structural requirements to activate peroxo reactivity, the active peroxo intermediate in 4-aminobenzoate N-oxygenase (AurF) has been characterized spectroscopically and computationally. A magnetic circular dichroism study of reduced AurF shows that its electronic and geometric structures are poised to react rapidly with O 2. Nuclear resonance vibrational spectroscopic definition of the peroxo intermediate formed in this reaction shows that the active intermediate has a protonated peroxo bridge. Density functional theory computations on the structure established here show that the protonation activates peroxide for electrophilic/single-electron-transfer reactivity. As a result, this activation of peroxide by protonation is likely also relevant to the reactive peroxo intermediates in other binuclear non-heme iron enzymes.

Authors:
 [1];  [2];  [3]; ORCiD logo [3];  [3];  [3];  [3];  [4];  [5];  [5];  [6];  [6]; ORCiD logo [2];  [2]; ORCiD logo [7]
  1. Stanford Univ., Stanford, CA (United States); KAIST, Daejeon (Republic of Korea)
  2. Pennsylvania State Univ., University Park, PA (United States)
  3. Stanford Univ., Stanford, CA (United States)
  4. SPring-8/JASRO, Hyogo (Japan)
  5. Kyoto Univ., Osaka (Japan)
  6. Argonne National Lab. (ANL), Lemont, IL (United States)
  7. Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Institutes of Health (NIH); National Science Foundation (NSF); Japan Society for the Promotion of Science (JSPS) - KAKENHI
OSTI Identifier:
1369431
Alternate Identifier(s):
OSTI ID: 1377396
Grant/Contract Number:
AC02-76SF00515; CHE-1058931; MCB1404866; 24221005; GM40392; AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 20; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; O2 activation; diiron site; peroxo intermediate; nuclear resonance vibrational spectroscopy; O2; activation

Citation Formats

Park, Kiyoung, Li, Ning, Kwak, Yeonju, Srnec, Martin, Bell, Caleb B., Liu, Lei V., Wong, Shaun D., Yoda, Yoshitaka, Kitao, Shinji, Seto, Makoto, Hu, Michael, Zhao, Jiyong, Krebs, Carsten, Bollinger, Jr., J. Martin, and Solomon, Edward I. Peroxide Activation for Electrophilic Reactivity by the Binuclear Non-heme Iron Enzyme AurF. United States: N. p., 2017. Web. doi:10.1021/jacs.7b02997.
Park, Kiyoung, Li, Ning, Kwak, Yeonju, Srnec, Martin, Bell, Caleb B., Liu, Lei V., Wong, Shaun D., Yoda, Yoshitaka, Kitao, Shinji, Seto, Makoto, Hu, Michael, Zhao, Jiyong, Krebs, Carsten, Bollinger, Jr., J. Martin, & Solomon, Edward I. Peroxide Activation for Electrophilic Reactivity by the Binuclear Non-heme Iron Enzyme AurF. United States. doi:10.1021/jacs.7b02997.
Park, Kiyoung, Li, Ning, Kwak, Yeonju, Srnec, Martin, Bell, Caleb B., Liu, Lei V., Wong, Shaun D., Yoda, Yoshitaka, Kitao, Shinji, Seto, Makoto, Hu, Michael, Zhao, Jiyong, Krebs, Carsten, Bollinger, Jr., J. Martin, and Solomon, Edward I. Mon . "Peroxide Activation for Electrophilic Reactivity by the Binuclear Non-heme Iron Enzyme AurF". United States. doi:10.1021/jacs.7b02997. https://www.osti.gov/servlets/purl/1369431.
@article{osti_1369431,
title = {Peroxide Activation for Electrophilic Reactivity by the Binuclear Non-heme Iron Enzyme AurF},
author = {Park, Kiyoung and Li, Ning and Kwak, Yeonju and Srnec, Martin and Bell, Caleb B. and Liu, Lei V. and Wong, Shaun D. and Yoda, Yoshitaka and Kitao, Shinji and Seto, Makoto and Hu, Michael and Zhao, Jiyong and Krebs, Carsten and Bollinger, Jr., J. Martin and Solomon, Edward I.},
abstractNote = {Binuclear non-heme iron enzymes activate O2 for diverse chemistries that include oxygenation of organic substrates and hydrogen atom abstraction. This process often involves the formation of peroxo-bridged biferric intermediates, only some of which can perform electrophilic reactions. To elucidate the geometric and electronic structural requirements to activate peroxo reactivity, the active peroxo intermediate in 4-aminobenzoate N-oxygenase (AurF) has been characterized spectroscopically and computationally. A magnetic circular dichroism study of reduced AurF shows that its electronic and geometric structures are poised to react rapidly with O2. Nuclear resonance vibrational spectroscopic definition of the peroxo intermediate formed in this reaction shows that the active intermediate has a protonated peroxo bridge. Density functional theory computations on the structure established here show that the protonation activates peroxide for electrophilic/single-electron-transfer reactivity. As a result, this activation of peroxide by protonation is likely also relevant to the reactive peroxo intermediates in other binuclear non-heme iron enzymes.},
doi = {10.1021/jacs.7b02997},
journal = {Journal of the American Chemical Society},
number = 20,
volume = 139,
place = {United States},
year = {Mon May 01 00:00:00 EDT 2017},
month = {Mon May 01 00:00:00 EDT 2017}
}

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  • Binuclear non-heme iron enzymes activate O-2 for diverse chemistries that include oxygenation of organic substrates and hydrogen atom abstraction. This process often involves the formation of peroxo-bridged biferric intermediates, only some of which can perform electrophilic reactions. To elucidate the geometric and electronic structural requirements to activate peroxo reactivity, the active peroxo intermediate in 4-aminobenzoate N-oxygenase (AurF) has been characterized spectroscopically and computationally. A magnetic circular dichroism study of reduced AurF shows that its electronic and geometric structures are poised to react rapidly with O-2. Nuclear resonance vibrational spectroscopic definition of the peroxo intermediate formed in this reaction shows thatmore » the active intermediate has a protonated peroxo bridge. Density functional theory computations on the structure established here show that the protonation activates peroxide for electrophilic/single-electron-transfer reactivity. This activation of peroxide by protonation is likely also relevant to the reactive peroxo intermediates in other binuclear non-heme iron enzymes.« less
  • We report that DFsc (single-chain due ferri) proteins allow for modeling binuclear non-heme iron enzymes with a similar fold. Three 4A → 4G variants of DFsc were studied to investigate the effects of (1) increasing the size of the substrate/solvent access channel (G4DFsc), (2) including an additional His residue in the first coordination sphere along with three additional helix-stabilizing mutations [3His-G4DFsc(Mut3)], and (3) the three helix-stabilizing mutations alone [G4DFsc-(Mut3)] on the biferrous structures and their O 2 reactivities. Near-infrared circular dichroism and magnetic circular dichroism (MCD) spectroscopy show that the 4A → 4G mutations increase coordination of the diiron sitemore » from 4-coordinate/5-coordinate to 5-coordinate/5-coordinate, likely reflecting increased solvent accessibility. While the three helix-stabilizing mutations [G4DFsc(Mut3)] do not affect the coordination number, addition of the third active site His residue [3His-G4DFsc(Mut3)] results in a 5-coordinate/6-coordinate site. Although all 4A → 4G variants have significantly slower pseudo-first-order rates when reacting with excess O 2 than DFsc (~2 s ₋1), G4DFsc and 3His-G4DFsc(Mut3) have rates (~0.02 and ~0.04 s ₋1) faster than that of G4DFsc(Mut3) (~0.002 s ₋1). These trends in the rate of O 2 reactivity correlate with exchange coupling between the Fe(II) sites and suggest that the two-electron reduction of O 2 occurs through end-on binding at one Fe(II) rather than through a peroxy-bridged intermediate. Finally, UV–vis absorption and MCD spectroscopies indicate that an Fe(III)Fe(III)-OH species first forms in all three variants but converts into an Fe(III)-μ-OH-Fe(III) species only in the 2-His forms, a process inhibited by the additional active site His ligand that coordinatively saturates one of the iron centers in 3His-G4DFsc(Mut3).« less
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  • The geometric and electronic structure of high-spin ferrous complexes of bleomycin (Fe{sup II}BLM) and the structural analog PMAH ([Fe{sup II}PMA]{sup +}, where PMAH is a macrocyclic ligand with pyrimidine, imidazole, deprotonated amide, and secondary and primary amine functionalities) have been investigated by optical (Abs) and X-ray (XAS) absorption, magnetic circular dichroism (MCD), and resonance Raman (rR) spectroscopies. The lability of high-spin iron combined with steric constraints of the BLM ligand framework and its weaker axial interaction with solvent support a dissociative mechanism for O{sub 2} reactivity. Our spectroscopic studies of solid [Fe{sup II}PMA]{sup +} have defined the nature of suchmore » a five-coordinate intermediate as square pyramidal which provides an open coordination position for reaction with O{sub 2}. A major electronic structure difference between Fe{sup II}BLM (and [Fe{sup II}PMA]{sup +}) and other non-heme ferrous sites is the presence of low-energy CT transitions which reflect strong iron(II) {yields} pyrimidine backbonding. Despite generally being considered a non-heme iron system due to the absence of an extensive delocalized {pi} network, the existence of low-energy MLCT transitions with reasonable intensity, hence the presence of some backbonding, identifies BLM as an important link bridging the chemistry of non-heme and heme active sites. 113 refs., 17 figs., 4 tabs.« less