Poster: Photosynthesis

Abs # 320: Crystal structure of the PsbP protein of photosystem II at 2.0-Å resolution

Presenter:	Ifuku, Kentaro , ifuku@kais.kyoto-u.ac.jp
Authors	Ifuku, Kentaro  (A)   Nakatsu, Toru  (B)   Yamamoto, Yumiko  (A)   Kato, Hiroaki  (B)   Sato, Fumihiko  (A)
Affiliations:	(A): Graduate Schcool of Biostudies, Kyoto University (B): RIKEN Harima Institute at SPring-8

The PsbP protein is found in the oxygen-evolving complex (OEC) of photosystem II (PSII) from higher plants and green algae, but not in that from cyanobacteria. PsbP, together with PsbQ, helps retain calcium and chloride ions that are essential cofactors for the water-splitting reaction. Cyanobacteria have two other OEC proteins: cyt c550 and the 12-kDa protein instead of PsbP and PsbQ. The functions of cyt c550 and the 12-kDa protein resemble those of PsbP and PsbQ, but they are apparently different from PsbP and PsbQ in both primary sequences and binding features to the PS II complex. Recent progress in X-ray crystallography resolved a PSII structure of cyanobacteria to 3.7 Å. However, PSII of higher plants and green algae is still far from being resolved. So far, Crystallization of PsbP and its 3D structure have not been reported yet. In order to elucidate the 3D structure and its molecular evolution, PsbP was crystallized by the hanging-drop vapour-diffusion technique. Diffraction data to 2.0 Å were collected from a native crystal belonging to space group P2₁22₁with unit-cell parameters a = 74.15, b = 91.36, c = 52.16 Å. A heavy-atom derivative was prepared, and the phase problem was solved by multi-wavelength anomalous dispersion (MAD) experiments using synchrotron X-ray radiation at SPring-8 (Hyogo, Japan). The crystal structure of PsbP was determined at 2.0-Å resolution. The obtained PsbP structure is mainly composed of β-sheet. Structures similar to PsbP do not exist in cyanobacterial PSII. Physiological role of PsbP in planta will be also discussed with the transgenic tobacco with low-PsbP expression.