TY - JOUR
T1 - 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
AU - Aznar, Constantino P.
AU - Britt, R. David
AU - Zhang, C.
AU - Dismukes, C.
AU - Fromme, P.
AU - Brudvig, G. W.
AU - Evans, M. W.C.
N1 - Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 2002/10/29
Y1 - 2002/10/29
N2 - 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.
AB - 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.
KW - Multiline electron paramagnetic resonance signal
KW - Oxygen-evolving complex
KW - Pulsed electron paramagnetic resonance
KW - Water oxidation
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U2 - 10.1098/rstb.2002.1144
DO - 10.1098/rstb.2002.1144
M3 - Article
C2 - 12437874
AN - SCOPUS:0037195370
VL - 357
SP - 1359
EP - 1366
JO - Philosophical Transactions of the Royal Society B: Biological Sciences
JF - Philosophical Transactions of the Royal Society B: Biological Sciences
SN - 0962-8436
IS - 1426
ER -