title: Proton Matrix ENDOR Studies on Ca2+-depleted and Sr2+-substituted Manganese Cluster in Photosystem II.
abstract: Proton matrix ENDOR spectra were measured for Ca(2+)-depleted and Sr(2+)-substituted photosystem II (PSII) membrane samples from spinach and core complexes from Thermosynechococcus vulcanus in the S2 state. The ENDOR spectra obtained were similar for untreated PSII from T. vulcanus and spinach, as well as for Ca(2+)-containing and Sr(2+)-substituted PSII, indicating that the proton arrangements around the manganese cluster in cyanobacterial and higher plant PSII and Ca(2+)-containing and Sr(2+)-substituted PSII are similar in the S2 state, in agreement with the similarity of the crystal structure of both Ca(2+)-containing and Sr(2+)-substituted PSII in the S1 state. Nevertheless, slightly different hyperfine separations were found between Ca(2+)-containing and Sr(2+)-substituted PSII because of modifications of the water protons ligating to the Sr(2+) ion. Importantly, Ca(2+) depletion caused the loss of ENDOR signals with a 1.36-MHz separation because of the loss of the water proton W4 connecting Ca(2+) and YZ directly. With respect to the crystal structure and the functions of Ca(2+) in oxygen evolution, it was concluded that the roles of Ca(2+) and Sr(2+) involve the maintenance of the hydrogen bond network near the Ca(2+) site and electron transfer pathway to the manganese cluster.
authors.affiliation: Graduate School of Science, Nagoya University, Furo-cho, Chikusa, Nagoya, 464-8602, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Nagashima
authors.affiliation: Photosynthesis Research Center, Graduate School of Natural Science and Technology/Faculty of Science, Okayama University, Okayama 700-8530, Japan.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Nakajima
authors.affiliation: Photosynthesis Research Center, Graduate School of Natural Science and Technology/Faculty of Science, Okayama University, Okayama 700-8530, Japan.
authors.forename: Jian-Ren
authors.initials: JR
authors.lastname: Shen
authors.affiliation: Graduate School of Science, Nagoya University, Furo-cho, Chikusa, Nagoya, 464-8602, Japan. Electronic address: mino@bio.phys.nagoya-u.ac.jp.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Mino
mesh_terms: D002118:Calcium / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D006860:Hydrogen Bonding; D008345:Manganese / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D011522:Protons; D013324:Strontium / Q000378:metabolism*
chemical_list: D045332:Photosystem II Protein Complex; D011522:Protons; D008345:Manganese; D002118:Calcium; D013324:Strontium
keywords: Ca2+ depletion; Sr2+ substitution; electron nuclear double resonance (ENDOR); electron paramagnetic resonance (EPR); electron transfer; manganese cluster; metalloenzyme; photosystem II