ENDOR and ESEEM investigation of the Ni-containing superoxide dismutase

Hong In Lee*, Jin Won Lee, Tran Chin Yang, Sa Ouk Kang, Brian M. Hoffman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

Superoxide dismutases (SODs) protect cells against oxidative stress by disproportionating O2 - to H2O2 and O2. The recent finding of a nickel-containing SOD (Ni-SOD) has widened the diversity of SODs in terms of metal contents and SOD catalytic mechanisms. The coordination and geometrical structure of the metal site and the related electronic structure are the keys to understanding the dismutase mechanism of the enzyme. We performed Q-band 14N,1/2H continuous wave (CW) and pulsed electron-nuclear double resonance (ENDOR) and X-band 14N electron spin echo envelope modulation (ESEEM) on the resting-state Ni-SOD extracted from Streptomyces seoulensis. In-depth analysis of the data obtained from the multifrequency advanced electron paramagnetic resonance techniques detailed the electronic structure of the active site of Ni-SOD. The analysis of the field-dependent Q-band 14N CW ENDOR yielded the nuclear hyperfine and quadrupole coupling tensors of the axial Nδ of the His-1 imidazole ligand. The tensors are coaxial with the g-tensor frame, implying the g-tensor direction is modulated by the imidazole plane. X-band 14N ESEEM characterized the hyperfine coupling of Nε of His-1 imidazole. The nuclear quadrupole coupling constant of the nitrogen suggests that the hydrogen-bonding between Nε-H and OGlu-17 present for the reduced-state Ni-SOD is weakened or broken upon oxidizing the enzyme. Q-band 1H CW ENDOR and pulsed 2H Mims ENDOR showed a strong hyperfine coupling to the protons(s) of the equatorially coordinated His-1 amine and a weak hyperfine coupling to either the proton(s) of a water in the pocket at the side opposite the axial Nδ or the proton of a water hydrogen-bonded to the equatorial thiolate ligand.

Original languageEnglish (US)
Pages (from-to)175-182
Number of pages8
JournalJournal of Biological Inorganic Chemistry
Volume15
Issue number2
DOIs
StatePublished - Feb 2010

Keywords

  • Electron paramagnetic resonance
  • Electron spin echo envelope modulation
  • Electron-nuclear double resonance
  • Nickel-containing superoxide dismutase

ASJC Scopus subject areas

  • Biochemistry
  • Inorganic Chemistry

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