PARENT SESSION
Posters P5A Type II reaction centres : Structure. Abstracts (289-312)

Structure-based analysis on the PsbP protein of Photosystem II from higher plants. Kentaro Ifuku^{*,1, 2}, Toru Nakatsu^{2, 3}, Yumiko Yamamoto¹, Seiko Ishihara¹, Ren Shimamoto¹, Hiroaki Kato^{2, 3}, Fumihiko Sato¹, ¹ Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, Japan² RIKEN Harima Institute at SPring-8, Sayo-gun, Hyogo, Japan³ Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto, Japan

ABSTRACT- PsbP is a membrane-extrinsic subunit of the water-oxidizing complex photosystem II (PS II). PsbP is specifically found in higher plants and green algal PS II, whereas genomic and proteomic studies revealed the presence of PsbP-like proteins in both cyanobacteria and higher plants. Because PsbP does not exist in any 3D structures of cyanobacterial PS II and no structure at reasonable resolution has been reported about higher plants and green algal PS II, the 3D structure of PsbP has been unknown. Recently, We reported the crystal structure of PsbP from Nicotiana tabacum at a resolution of 1.6 angstrom [Ifuku, K. et al., (2004) EMBO Rep., 5, 362-367]. Its structure is mainly composed of beta-sheet, and is not similar to any structures in cyanobacterial PS II. However, the electrostatic surface potential of PsbP is similar to that of cyanobacterial PsbV (cyt c550), which has a function similar to PsbP in cyanobacterial PS II. Since both PsbP and PsbV are known to be bound to PS II with electrostatic interaction, PsbP is likely to interact with higher plants PS II in a manner similar to PsbV with cyanobacterial PS II. The N-terminal region of PsbP, which is essential for the activity retaining Ca²⁺ and Cl^- in PS II [Ifuku, K. & Sato, F. (2002) Plant & Cell Physiol., 43, 1244-1249], is not seen because of disorder. This region would adopt a native structure required for ions retention only when PsbP is bound to PS II. A structural homology search with the DALI algorithm indicated that the folding of PsbP is very similar to that of Mog1p, a regulatory protein for the nuclear transport of Ran GTPase. The biological importance of this similarity is not clear; however, PsbO, which directly interacts with PsbP, was recently identified as GTP-binding protein [Spetea, C. et al., (2004) PNAS, 101, 1409-1414]. Based on structural information, further biochemical and molecular biological analyses on PsbP are underway.

KEY WORDS: extrinsic protein, crystal structure, photosystem II, PsbP