title: Structural changes of D1 C-terminal alpha-carboxylate during S-state cycling in photosynthetic oxygen evolution.
abstract: Changes in the chemical structure of alpha-carboxylate of the D1 C-terminal Ala-344 during S-state cycling of photosynthetic oxygen-evolving complex were selectively measured using light-induced Fourier transform infrared (FTIR) difference spectroscopy in combination with specific [(13)C]alanine labeling and site-directed mutagenesis in photosystem II core particles from Synechocystis sp. PCC 6803. Several bands for carboxylate symmetric stretching modes in an S(2)/S(1) FTIR difference spectrum were affected by selective (13)C labeling of the alpha-carboxylate of Ala with l-[1-(13)C]alanine, whereas most of the isotopic effects failed to be induced in a site-directed mutant in which Ala-344 was replaced with Gly. Labeling of the alpha-methyl of Ala with l-[3-(13)C]alanine had much smaller effects on the spectrum to induce isotopic bands due to a symmetric CH(3) deformation coupled with the alpha-carboxylate. The isotopic bands for the alpha-carboxylate of Ala-344 showed characteristic changes during S-state cycling. The bands appeared prominently upon the S(1)-to-S(2) transition and to a lesser extent upon the S(2)-to-S(3) transition but reappeared at slightly upshifted frequencies with the opposite sign upon the S(3)-to-S(0) transition. No obvious isotopic band appeared upon the S(0)-to-S(1) transition. These results indicate that the alpha-carboxylate of C-terminal Ala-344 is structurally associated with a manganese ion that becomes oxidized upon the S(1)-to-S(2) transition and reduced reversely upon the S(3)-to-S(0) transition but is not associated with manganese ion(s) oxidized during the S(0)-to-S(1) (and S(2)-to-S(3)) transition(s). Consistently, l-[1-(13)C]alanine labeling also induced spectral changes in the low frequency (670-350 cm(-1)) S(2)/S(1) FTIR difference spectrum.
authors.affiliation: Laboratory for Photo-Biology (1), RIKEN Photodynamics Research Center, The Institute of Physical and Chemical Research, 519-1399 Aoba, Aramaki, Aoba, Sendai 980-0845, Japan.
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Kimura
authors.forename: Naoki
authors.initials: N
authors.lastname: Mizusawa
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Yamanari
authors.forename: Asako
authors.initials: A
authors.lastname: Ishii
authors.forename: Taka-aki
authors.initials: TA
authors.lastname: Ono
mesh_terms: D000409:Alanine / Q000737:chemistry*; D002247:Carbon Isotopes; D002264:Carboxylic Acids / Q000737:chemistry*; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared; D046939:Synechocystis / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D002264:Carboxylic Acids; D045322:Photosynthetic Reaction Center Complex Proteins; D000409:Alanine; D010100:Oxygen