Site-specific mutations in the D1 polypeptide affect the susceptibility of Synechocystis 6803 cells to photoinhibition.

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.