Abstract
Photosystem II(PSII) performs light-induced electron transfer and water-splitting reactions, leading to the formation of molecular oxygen. After initial light excitation and charge separation at the reaction center of PSII, an electron is transferred from QA to QB. QB leaves the complex to cyt b6f as PQH2 after uptake of two protons and two electrons.
Our final goal is to realize an artificial system of photosynthesis using PSII with functional molecules newly designed and synthesized. The electron acceptor parts of the molecules, connecting electron transfer and reduction parts in series, may bind to the QB site. In order to obtain structural information for binding mode at the QB site, we introduced four herbicides, DCMU, Bromacil, Bromoxynil, and Terbutryne, into PSII crystals by soaking, well known to bind into the QB site and to inhibit electron transfer beyond QA. X-ray diffraction data were collected at BL44XU, SPring-8. Crystal structures were solved with molecular replacement technique and refined around 1.9- 2.3A resolutions. Based on the structures of herbicides found at the QB site, we will discuss inhibitor binding modes and electron transfer mechanism from QA to QB.
