Simulations of the 1H electron spin echo-electron nuclear double resonance and 2H electron spin echo envelope modulation spectra of exchangeable hydrogen nuclei coupled to the S2-state photosystem II manganese cluster

Constantino P. Aznar, R. David Britt, C. Zhang, C. Dismukes, P. Fromme, G. W. Brudvig, M. W.C. Evans

Research output: Contribution to journalArticle

47 Scopus citations

Abstract

The pulsed EPR methods of electron spin echo envelope modulation (ESEEM) and electron spin echo-electron nuclear double resonance (ESE-ENDOR) are used to investigate the proximity of exchangeable hydrogens around the paramagnetic S2-state Mn cluster of the photosystem II oxygen-evolving complex. Although ESEEM and ESE-ENDOR are both pulsed electron paramagnetic resonance techniques, the specific mechanisms by which nuclear spin transitions are observed are quite different. We are able to generate good simulations of both 1H ESE-ENDOR and 2H ESEEM signatures of exchangeable hydrogens at the S2-state cluster. The convergence of simulation parameters for both methods provides a high degree of confidence in the simulations. Several exchangeable protons-deuterons with strong dipolar couplings are observed. In the simulations, two of the close (≈2.5 Å) hydrogen nuclei exhibit strong isotropic couplings and are therefore most probably associated with direct substrate ligation to paramagnetic Mn. Another two of the close (≈2.7 Å) hydrogen nuclei show no isotropic couplings and are therefore most probably not contained in Mn ligands. We suggest that these proximal hydrogens may be associated with a Ca2+-bound substrate, as indicated in recent mechanistic proposals for O2 formation.

Original languageEnglish (US)
Pages (from-to)1359-1366
Number of pages8
JournalPhilosophical Transactions of the Royal Society B: Biological Sciences
Volume357
Issue number1426
DOIs
StatePublished - Oct 29 2002
Externally publishedYes

    Fingerprint

Keywords

  • Multiline electron paramagnetic resonance signal
  • Oxygen-evolving complex
  • Pulsed electron paramagnetic resonance
  • Water oxidation

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Agricultural and Biological Sciences(all)

Cite this