title: Genetically introduced hydrogen bond interactions reveal an asymmetric charge distribution on the radical cation of the special-pair chlorophyll P680.
abstract: The special-pair chlorophyll (Chl) P680 in photosystem II has an extremely high redox potential (Em) to enable water oxidation in photosynthesis. Significant positive-charge localization on one of the Chl constituents, PD1or PD2, in P680+has been proposed to contribute to this highEmTo identify the Chl molecule on which the charge is mainly localized, we genetically introduced a hydrogen bond to the 131-keto C=O group of PD1and PD2by changing the nearby D1-Val-157 and D2-Val-156 residues to His, respectively. Successful hydrogen bond formation at PD1and PD2in the obtained D1-V157H and D2-V156H mutants, respectively, was monitored by detecting 131-keto C=O vibrations in Fourier transfer infrared (FTIR) difference spectra upon oxidation of P680 and the symmetrically located redox-active tyrosines YZand YD, and they were simulated by quantum-chemical calculations. Analysis of the P680+/P680 FTIR difference spectra of D1-V157H and D2-V156H showed that upon P680+formation, the 131-keto C=O frequency upshifts by a much larger extent in PD1(23 cm-1) than in PD2(<9 cm-1). In addition, thermoluminescence measurements revealed that the D1-V157H mutation increased theEmof P680 to a larger extent than did the D2-V156H mutation. These results, together with the previous results for the mutants of the His ligands of PD1and PD2, lead to a definite conclusion that a charge is mainly localized to PD1in P680<sup/>.
authors.affiliation: From the Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan nagao@bio.phys.nagoya-u.ac.jp.
authors.forename: Ryo
authors.initials: R
authors.lastname: Nagao
authors.affiliation: From the Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Motoki
authors.initials: M
authors.lastname: Yamaguchi
authors.affiliation: From the Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Shin
authors.initials: S
authors.lastname: Nakamura
authors.affiliation: From the Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Hanayo
authors.initials: H
authors.lastname: Ueoka-Nakanishi
authors.affiliation: From the Division of Material Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan tnoguchi@bio.phys.nagoya-u.ac.jp.
authors.forename: Takumi
authors.initials: T
authors.lastname: Noguchi
mesh_terms: D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D002734:Chlorophyll / Q000737:chemistry* / Q000235:genetics; D006860:Hydrogen Bonding; D020125:Mutation, Missense; D010084:Oxidation-Reduction; D046939:Synechocystis / Q000737:chemistry* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D002734:Chlorophyll; C025167:P-680
keywords: FTIR; chlorophyll; cyanobacteria; hydrogen bond; photosynthesis; photosystem II; quantum chemical calculation; site-directed mutagenesis; special pair; thermoluminescence