1 research outputs found
Two Different Structures of the Oxygen-Evolving Complex in the Same Polypeptide Frameworks of Photosystem II
The oxygen-evolving complex (OEC)
forms the heart of photosystem
II (PSII) in photosynthesis. The crystal structure of PSII from Thermosynechococcus vulcanus has been reported at
a resolution of 1.9 Å and at an averaged X-ray dose of 0.43 MGy.
The OEC structure is suggested to be partially reduced to Mn(II) by
EXAFS and DFT computational studies.
Recently, the “radiation-damage-free” structures have
been published at 1.95 Å resolution using XFEL, but reports continued
to appear that the OEC is reduced to the S<sub>0</sub>-state of the
Kok cycle. To elucidate much more precise structure of the OEC, in
this study two structures were determined at extremely low X-ray doses
of 0.03 and 0.12 MGy using conventional synchrotron radiation source.
The results indicated that the X-ray reduction effects on the OEC
were very small in the low dose region below 0.12 MGy, that is, a
threshold existed for the OEC structural changes caused by X-ray exposure.
The OEC structures of the two identical monomers in the crystal were
clearly different under the threshold of the radiation dose, although
the surrounding polypeptide frameworks of PSII were the same. The
assumption that the OECs in the crystal were in the dark-stable S<sub>1</sub>-state of the Kok cycle should be re-evaluated