title: Light-induced oxidative stress, N-formylkynurenine, and oxygenic photosynthesis.
abstract: Light stress in plants results in damage to the water oxidizing reaction center, photosystem II (PSII). Redox signaling, through oxidative modification of amino acid side chains, has been proposed to participate in this process, but the oxidative signals have not yet been identified. Previously, we described an oxidative modification, N-formylkynurenine (NFK), of W365 in the CP43 subunit. The yield of this modification increases under light stress conditions, in parallel with the decrease in oxygen evolving activity. In this work, we show that this modification, NFK365-CP43, is present in thylakoid membranes and may be formed by reactive oxygen species produced at the Mn(4)CaO(5) cluster in the oxygen-evolving complex. NFK accumulation correlates with the extent of photoinhibition in PSII and thylakoid membranes. A modest increase in ionic strength inhibits NFK365-CP43 formation, and leads to accumulation of a new, light-induced NFK modification (NFK317) in the D1 polypeptide. Western analysis shows that D1 degradation and oligomerization occur under both sets of conditions. The NFK modifications in CP43 and D1 are found 17 and 14 Angstrom from the Mn(4)CaO(5) cluster, respectively. Based on these results, we propose that NFK is an oxidative modification that signals for damage and repair in PSII. The data suggest a two pathway model for light stress responses. These pathways involve differential, specific, oxidative modification of the CP43 or D1 polypeptides.
authors.affiliation: School of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia, United States of America.
authors.forename: Tina M
authors.initials: TM
authors.lastname: Dreaden Kasson
authors.forename: Sascha
authors.initials: S
authors.lastname: Rexroth
authors.forename: Bridgette A
authors.initials: BA
authors.lastname: Barry
mesh_terms: D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D007737:Kynurenine / Q000031:analogs & derivatives* / Q000378:metabolism; D008027:Light; D008969:Molecular Sequence Data; D018384:Oxidative Stress / Q000528:radiation effects*; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis; D059748:Proteolysis; D053719:Tandem Mass Spectrometry
chemical_list: C007772:N'-formylkynurenine; D007737:Kynurenine; D010100:Oxygen