Nobuo Kamiya
Osaka City University, Japan
Title: Two alternative structures of oxygen-evolving complex in photosystem II found by X-ray crystallography at extremely low doses
Biography
Biography: Nobuo Kamiya
Abstract
Oxygen-evolving complex (OEC) is the heart of photosystem II (PSII), which extracts electrons from water molecules using solar light energy in photosynthesis. Crystal structure of PSII has been resolved at a resolution of 1.9 Ã… (Umena, Kawakami, Shen & Kamiya, Nature (2011)), and chemical formula of OEC is fixed as Mn4CaO5(H2O)4 for the first time. Based on the structural information (PDB-ID: 3WU2), researchers make efforts to elucidate the mechanism of oxygen-evolving reactions in OEC according to the Kok cycle model and to develop new catalysts for water splitting, which are required in artificial photosynthesis. Because OEC is highly sensitive to X-ray irradiation, however, X-ray reduction of OEC and structure changes induced have been discussed on the results from XAFS and DFT computational studies for the past five years. In order to overcome the X-ray reduction problem, we prepared highly isomorphous crystals of PSII and succeeded recently to collect two datasets of diffraction intensities at extremely low doses of 0.06 and 0.24 MGy (0.81 MGy for the previous dataset) at beamlins of SPring-8, BL38B1 and BL44XU. Obtained structures were compared with each other and with 3WU2, and two alternative structures of OEC were found in two monomers in an asymmetric unit of crystal. I will discuss in my talk about the meanings of the alternative structures and X-ray reduction effects on OEC.