TY - JOUR
T1 - Rapid-Scan Time-Resolved ATR-FTIR Study on the Photoassembly of the Water-Oxidizing Mn4CaO5Cluster in Photosystem II
AU - Sato, Akihiko
AU - Nakano, Yuki
AU - Nakamura, Shin
AU - Noguchi, Takumi
N1 - Funding Information:
Quantum chemical calculations were carried out at the Research Center for Computational Science, Okazaki, Japan. This study was supported by JSPS KAKENHI Grant Number JP17H06435, JP17H03662, and JP17H06433 (to T.N.).
Publisher Copyright:
© 2021 American Chemical Society. All rights reserved.
PY - 2021/4/29
Y1 - 2021/4/29
N2 - The catalytic center of photosynthetic water oxidation, the Mn4CaO5 cluster, is assembled in photosystem II (PSII) through a light-driven process called photoactivation, whose mechanism remains elusive. Here, we used rapid-scan time-resolved Fourier transform infrared (FTIR) spectroscopy combined with the attenuated total reflection (ATR) technique to monitor the photoactivation process. Rapid-scan ATR-FTIR spectra of apo-PSII with Mn2+ upon flash illumination showed spectral features typical of carboxylate stretching vibrations, which were attributed to two carboxylate ligands, D1-D170 and D1-E189, by quantum chemical calculations. The FTIR signal decayed with a time constant of ∼0.7 s, showing that the subsequent "dark rearrangement"step occurred with a low quantum yield and Mn3+ ions were mostly released during this decay. Simulation of the kinetic process provided a slow intrinsic rate of the dark rearrangement, which was attributed to a large protein conformational change. The photoassembly mechanism of the Mn4CaO5 cluster is proposed based on these findings.
AB - The catalytic center of photosynthetic water oxidation, the Mn4CaO5 cluster, is assembled in photosystem II (PSII) through a light-driven process called photoactivation, whose mechanism remains elusive. Here, we used rapid-scan time-resolved Fourier transform infrared (FTIR) spectroscopy combined with the attenuated total reflection (ATR) technique to monitor the photoactivation process. Rapid-scan ATR-FTIR spectra of apo-PSII with Mn2+ upon flash illumination showed spectral features typical of carboxylate stretching vibrations, which were attributed to two carboxylate ligands, D1-D170 and D1-E189, by quantum chemical calculations. The FTIR signal decayed with a time constant of ∼0.7 s, showing that the subsequent "dark rearrangement"step occurred with a low quantum yield and Mn3+ ions were mostly released during this decay. Simulation of the kinetic process provided a slow intrinsic rate of the dark rearrangement, which was attributed to a large protein conformational change. The photoassembly mechanism of the Mn4CaO5 cluster is proposed based on these findings.
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U2 - 10.1021/acs.jpcb.1c01624
DO - 10.1021/acs.jpcb.1c01624
M3 - Article
C2 - 33861065
AN - SCOPUS:85105094933
SN - 1520-6106
VL - 125
SP - 4031
EP - 4045
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 16
ER -