title: Binding and functional properties of five extrinsic proteins in oxygen-evolving photosystem II from a marine centric diatom, Chaetoceros gracilis.
abstract: Oxygen-evolving photosystem II (PSII) isolated from a marine centric diatom, Chaetoceros gracilis, contains a novel extrinsic protein (Psb31) in addition to four red algal type extrinsic proteins of PsbO, PsbQ', PsbV, and PsbU. In this study, the five extrinsic proteins were purified from alkaline Tris extracts of the diatom PSII by anion and cation exchange chromatographic columns at different pH values. Reconstitution experiments in various combinations with the purified extrinsic proteins showed that PsbO, PsbQ', and Psb31 rebound directly to PSII in the absence of other extrinsic proteins, indicating that these extrinsic proteins have their own binding sites in PSII intrinsic proteins. On the other hand, PsbV and PsbU scarcely rebound to PSII alone, and their effective bindings required the presence of all of the other extrinsic proteins. Interestingly, PSII reconstituted with Psb31 alone considerably restored the oxygen evolving activity in the absence of PsbO, indicating that Psb31 serves as a substitute in part for PsbO in supporting oxygen evolution. A significant difference found between PSIIs reconstituted with Psb31 and with PsbO is that the oxygen evolving activity of the former is scarcely stimulated by Cl(-) and Ca(2+) ions but that of the latter is largely stimulated by these ions, although rebinding of PsbV and PsbU activated oxygen evolution in the absence of Cl(-) and Ca(2+) ions in both the former and latter PSIIs. Based on these results, we proposed a model for the association of the five extrinsic proteins with intrinsic proteins in diatom PSII and compared it with those in PSIIs from the other organisms.
authors.affiliation: Department of Life Sciences (Biology), Graduate School of Art and Sciences, University of Tokyo, Komaba, Meguro, Tokyo 153-8902, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Nagao
authors.forename: Akira
authors.initials: A
authors.lastname: Moriguchi
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Tomo
authors.forename: Ayako
authors.initials: A
authors.lastname: Niikura
authors.forename: Saori
authors.initials: S
authors.lastname: Nakajima
authors.forename: Takehiro
authors.initials: T
authors.lastname: Suzuki
authors.forename: Akinori
authors.initials: A
authors.lastname: Okumura
authors.forename: Masako
authors.initials: M
authors.lastname: Iwai
authors.forename: Jian-Ren
authors.initials: JR
authors.lastname: Shen
authors.forename: Masahiko
authors.initials: M
authors.lastname: Ikeuchi
authors.forename: Isao
authors.initials: I
authors.lastname: Enami
mesh_terms: D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism*; D017377:Diatoms / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D020418:Algal Proteins; D045332:Photosystem II Protein Complex; D010100:Oxygen