Photosystem II activity and turnover of the D1 protein are impaired in the psbA Y112L mutant of Synechocystis PCC6803 sp.
Site-directed psbA mutants at the tyrosine Y112 position have been generated in Synechocystis PCC6803 cells. The mutation Y112F does not affect photosystem II (PSII) activity as compared with control 4 delta 1K cells. However, the Y112L mutant exhibits a photosynthetically impaired phenotype. PSII activity is not detectable in this mutant when grown at 30 mumol photons m-2 s-1, while low levels of the D1 and D2 proteins and oxygen evolution activity are present in the mutant cells grown at a low light intensity (0.5-1 mumol m-2 s-1). The recombination of the QB-/S2,3 states of PSII in the Y112L mutant cells as detected by thermoluminescence (TL) is altered. The TL signal emission maximum of these cells due to charge recombination of the S2,3/QB- occurs at 20 degrees C as compared to 35-40 degrees C for the wild-type cells, indicating a possible change in the S2,3/Yz equilibrium. The Y112L mutant cells are rapidly photoinactivated and impaired in the recovery of the PSII activity. These results suggest that replacement of the aromatic residue at position Y112 by a hydrophobic amino acid may alter the function of the donor-side activity and affects the degradation and replacement of the PSII core proteins.
Tal
S
S
Department of Genetics, Minerva, Avron Evenari Center of Photosynthesis Research, Hebrew University of Jerusalem, Israel.
Keren
N
N
Hirschberg
J
J
Ohad
I
I
D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D007930:Leucine / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism
D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D014443:Tyrosine; D007930:Leucine