TY - JOUR
T1 - Orientation resolving dipolar high-field EPR spectroscopy on disordered solids
T2 - II. Structure of spin-correlated radical pairs in photosystem i
AU - Savitsky, A.
AU - Niklas, J.
AU - Golbeck, J. H.
AU - Möbius, K.
AU - Lubitz, W.
PY - 2013/9/26
Y1 - 2013/9/26
N2 - The distance and relative orientation of functional groups within protein domains and their changes during chemical reactions determine the efficiency of biological processes. In this work on electron transfer proteins, we report the results of orientation resolving dipolar high-field EPR spectroscopy on the charge-separated state P700•+A1•- (P700, primary electron donor; A1, phylloquinone electron acceptor) in Photosystem I (PS I). Pulsed high-field EPR spectroscopy at W-band (95 GHz, 3.4 T) with extensions to PELDOR (pulsed electron-electron double resonance) and RIDME (relaxation-induced dipolar modulation enhancement) was utilized to obtain the parameters describing the three-dimensional structure of the laser-flash-induced transient radical pair P700•+A1•- in a frozen solution of deuterated PS I from the cyanobacterium Synechocystis sp. PCC 6803, which is performing oxygenic photosynthesis. The measured distances and relative orientations of the weakly coupled radical ions in the radical pair P700•+A1•- are compared with previously reported geometries and with those of the precursor cofactors P700 and A1 known from X-ray crystallography. Cyclic electron transfer was found to proceed exclusively via the A-branch of the cofactor chain of PS I at cryogenic temperature. The position and orientation of the reduced phylloquinone coincide with those of the precursor, revealing that no substantial orientational changes of the phylloquinone molecule upon charge separation occur. Several distinct orientations of the P700•+ g-tensor axes with respect to the molecular frame of the primary donor were found experimentally, which we explain by several conformational substates of the P700•+ radical structure having slightly different electron spin density distributions.
AB - The distance and relative orientation of functional groups within protein domains and their changes during chemical reactions determine the efficiency of biological processes. In this work on electron transfer proteins, we report the results of orientation resolving dipolar high-field EPR spectroscopy on the charge-separated state P700•+A1•- (P700, primary electron donor; A1, phylloquinone electron acceptor) in Photosystem I (PS I). Pulsed high-field EPR spectroscopy at W-band (95 GHz, 3.4 T) with extensions to PELDOR (pulsed electron-electron double resonance) and RIDME (relaxation-induced dipolar modulation enhancement) was utilized to obtain the parameters describing the three-dimensional structure of the laser-flash-induced transient radical pair P700•+A1•- in a frozen solution of deuterated PS I from the cyanobacterium Synechocystis sp. PCC 6803, which is performing oxygenic photosynthesis. The measured distances and relative orientations of the weakly coupled radical ions in the radical pair P700•+A1•- are compared with previously reported geometries and with those of the precursor cofactors P700 and A1 known from X-ray crystallography. Cyclic electron transfer was found to proceed exclusively via the A-branch of the cofactor chain of PS I at cryogenic temperature. The position and orientation of the reduced phylloquinone coincide with those of the precursor, revealing that no substantial orientational changes of the phylloquinone molecule upon charge separation occur. Several distinct orientations of the P700•+ g-tensor axes with respect to the molecular frame of the primary donor were found experimentally, which we explain by several conformational substates of the P700•+ radical structure having slightly different electron spin density distributions.
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U2 - 10.1021/jp401573z
DO - 10.1021/jp401573z
M3 - Article
C2 - 23642108
AN - SCOPUS:84884964365
SN - 1520-6106
VL - 117
SP - 11184
EP - 11199
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 38
ER -