Identification of hydrogen bonds to the Rieske cluster through the weakly coupled nitrogens detected by electron spin echo envelope modulation spectroscopy

Sergei A. Dikanov, Derrick R.J. Kolling, Burkhard Endeward, Rimma I. Samoilova, Thomas F. Prisner, Satish K. Nair, Antony R. Crofts

Research output: Contribution to journalArticlepeer-review

Abstract

The interaction of the reduced [2Fe-2S] cluster of isolated Rieske fragment from the bc1 complex of Rhodobacter sphaeroides with nitrogens (14N and 15N) from the local protein environment has been studied by X- and S-band pulsed EPR spectroscopy. The twodimensional electron spin echo envelope modulation spectra of uniformly 15N-labeled protein show two well resolved cross-peaks with weak couplings of ∼0.3-0.4 and 1.1 MHz in addition to couplings in the range of 6-8 MHz from two coordinating Nδ of histidine ligands. The quadrupole coupling constants for weakly coupled nitrogens determined from S-band electron spin echo envelope modulation spectra identify them as Nε of histidine ligands and peptide nitrogen (Np), respectively. Analysis of the line intensities in orientation-selected S-band spectra indicated that Np is the backbone N-atom of Leu-132 residue. The hyperfine couplings from N ε and Np demonstrate the predominantly isotropic character resulting from the transfer of unpaired spin density onto the 2s orbitals of the nitrogens. Spectra also show that other peptide nitrogens in the protein environment must carry a 5-10 times smaller amount of spin density than the Np of Leu-132 residue. The appearance of the excess unpaired spin density on the Np of Leu-132 residue indicates its involvement in hydrogen bond formation with the bridging sulfur of the Rieske cluster. The configuration of the hydrogen bond therefore provides a preferred path for spin density transfer. Observation of similar splittings in the 15N spectra of other Rieske-type proteins and [2Fe-2S] ferredoxins suggests that a hydrogen bond between the bridging sulfur and peptide nitrogen is a common structural feature of [2Fe-2S] clusters.

Original languageEnglish (US)
Pages (from-to)27416-27425
Number of pages10
JournalJournal of Biological Chemistry
Volume281
Issue number37
DOIs
StatePublished - Sep 15 2006

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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