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Site-specific mutations in the D1 polypeptide affect the susceptibility of Synechocystis 6803 cells to photoinhibition
Authors:Pirkko Mäenpää  Taina Kallio  Paula Mulo  Gaza Salih  Eva-Mari Aro  Esa Tyystjärvi  Christer Jansson
Institution:(1) Dept. of Biology, University of Turku, SF-20700 Turku, Finland;(2) Dept. of Biochemistry, University of Stockholm, S-10691 Stockholm, Sweden
Abstract:Photoinhibition of photosystem II in the cyanobacterium Synechocystis 6803 was followed after site-specific mutagenesis of the D1 polypeptide. Mutations were created in the stromal/cytosolic loop connecting helices D and E. Two mutations E243K and CA1, a deletion of the three glutamates 242–244 and a substitution Q241H, were made in the putative cleavage area of the D1 polypeptide. A third mutation E229D was made in the PEST-like sequence. Mutants and control cells were illuminated and FV/FM was recorded. Compared to the control, the mutants were less photoinhibited. Fluorescence relaxation after a single flash was delayed in CA1. Restoration of FV/FM after photoinhibition in the mutants was totally dependent on protein synthesis while control cells were able to recover partially also when protein synthesis was inhibited. In addition, the protein synthesis-dependent recovery of CA1 was slowed down. Our results indicate a correlation between the mutated amino acids and photoinhibition of photosystem II.
Keywords:chlorophyll a fluorescence  D1 polypeptide  photoinhibition  psbA genes  site-specific mutagenesis  Synechocystis 6803
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