title: Evidence that the C-terminus of the D1 polypeptide of photosystem II is ligated to the manganese ion that undergoes oxidation during the S1 to S2 transition: an isotope-edited FTIR study.
abstract: Isotope-edited FTIR difference spectroscopy was employed to determine if the C-terminal alpha-COO(-) group of the D1 polypeptide ligates the (Mn)(4) cluster in photosystem II (PSII) and, if so, if it ligates the Mn ion that undergoes an oxidation during the S(1) --> S(2) transition. Wild-type and mutant cells of the cyanobacterium Synechocystis sp. PCC 6803 were propagated photoautotrophically in the presence of L-[1-(13)C]alanine or unlabeled ((12)C) L-alanine. In wild-type cells, both the C-terminal alpha-COO(-) group of the D1 polypeptide at D1-Ala344 and all alanine-derived peptide carbonyl groups will be labeled. In D1-A344G and D1-A344S mutant cells, the C-terminal alpha-COO(-) group of the D1 polypeptide will not be labeled because this group is no longer provided by alanine. The resultant S(2)-minus-S(1) FTIR difference spectra of purified wild-type and mutant PSII particles showed that one symmetric carboxylate stretching mode that is altered during the S(1) --> S(2) transition is sensitive to L-[1-(13)C]alanine-labeling in wild-type PSII particles but not in D1-A344G and D1-A344S PSII particles. Because the only carboxylate group that can be labeled in the wild-type PSII particles but not in the mutant PSII particles is the C-terminal alpha-COO(-) group of the D1 polypeptide, we assign the L-[1-(13)C]alanine-sensitive symmetric carboxylate stretching mode to the alpha-COO(-) group of D1-Ala344. In unlabeled wild-type PSII particles, this mode appears at approximately 1356 cm(-1) in the S(1) state and at approximately 1339 or approximately 1320 cm(-1) in the S(2) state. These frequencies are consistent with unidentate ligation of the (Mn)(4) cluster by the alpha-COO(-) group of D1-Ala344 in both the S(1) and S(2) states. The apparent 17-36 cm(-1) downshift in frequency in response to the S(1) --> S(2) transition is consistent with the alpha-COO(-) group of D1-Ala344 ligating a Mn ion whose charge increases during the S(1) --> S(2) transition. Accordingly, we propose that the alpha-COO(-) group of D1-Ala344 ligates the Mn ion that undergoes an oxidation during the S(1) --> S(2) transition. Control experiments were conducted with Mn-depleted wild-type PSII particles. These experiments showed that tyrosine Y(D) may be structurally coupled to the carbonyl oxygen of an alanine-derived peptide carbonyl group.
authors.affiliation: Department of Biochemistry, University of California, Riverside, California 92521-0129, USA.
authors.forename: Hsiu-An
authors.initials: HA
authors.lastname: Chu
authors.forename: Warwick
authors.initials: W
authors.lastname: Hillier
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Debus
mesh_terms: D000409:Alanine / Q000235:genetics; D002244:Carbon; D002247:Carbon Isotopes; D002264:Carboxylic Acids / Q000737:chemistry; D002413:Cations, Divalent; D000458:Cyanobacteria / Q000737:chemistry / Q000235:genetics; D005998:Glycine / Q000235:genetics; D007553:Isotope Labeling / Q000379:methods; D008024:Ligands; D008345:Manganese / Q000737:chemistry*; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics; D010782:Photolysis; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000235:genetics; D012694:Serine / Q000235:genetics; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods
chemical_list: D002247:Carbon Isotopes; D002264:Carboxylic Acids; D002413:Cations, Divalent; D008024:Ligands; D010446:Peptide Fragments; D045332:Photosystem II Protein Complex; C422369:photosystem II, psbA subunit; D008345:Manganese; D012694:Serine; D002244:Carbon; D000409:Alanine; D005998:Glycine