title: Functional roles of D2-Lys317 and the interacting chloride ion in the water oxidation reaction of photosystem II as revealed by fourier transform infrared analysis.
abstract: Photosynthetic water oxidation in plants and cyanobacteria is catalyzed by a Mn4CaO5 cluster within the photosystem II (PSII) protein complex. Two Cl(-) ions bound near the Mn4CaO5 cluster act as indispensable cofactors, but their functional roles remain to be clarified. We have investigated the role of the Cl(-) ion interacting with D2-K317 (designated Cl-1) by Fourier transform infrared spectroscopy (FTIR) analysis of the D2-K317R mutant of Synechocystis sp. PCC 6803 in combination with Cl(-)/NO3(-) replacement. The D2-K317R mutation perturbed the bands in the regions of the COO(-) stretching and backbone amide vibrations in the FTIR difference spectrum upon the S1 → S2 transition. In addition, this mutation altered the (15)N isotope-edited NO3(-) bands in the spectrum of NO3(-)-treated PSII. These results provide the first experimental evidence that the Cl-1 site is coupled with the Mn4CaO5 cluster and its interaction is affected by the S1 → S2 transition. It was also shown that a negative band at 1748 cm(-1) arising from COOH group(s) was altered to a positive intensity by the D2-K317R mutation as well as by NO3(-) treatment, suggesting that the Cl-1 site affects the pKa of COOH/COO(-) group(s) near the Mn4CaO5 cluster in a common hydrogen bond network. Together with the observation that the efficiency of the S3 → S0 transition significantly decreased in the core complexes of D2-K317R upon moderate dehydration, it is suggested that D2-K317 and Cl-1 are involved in a proton transfer pathway from the Mn4CaO5 cluster to the lumen, which functions in the S3 → S0 transition.
authors.affiliation: Division of Material Science, Graduate School of Science, Nagoya University , Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Suzuki
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Yu
authors.forename: Takashi
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Hanayo
authors.initials: H
authors.lastname: Nakanishi
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Nixon
authors.forename: Takumi
authors.initials: T
authors.lastname: Noguchi
mesh_terms: D002712:Chlorides / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008239:Lysine / Q000737:chemistry*; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water / Q000737:chemistry*
chemical_list: D002712:Chlorides; D045332:Photosystem II Protein Complex; D014867:Water; D008239:Lysine