Open AccessReduced Turnover of the D1 Polypeptide and Photoactivation of Electron Transfer in Novel Herbicide Resistant Mutants of Synechocystis sp. PCC 6803
Author(s) -
Chjesa Marta Dalla,
Friso Giulia,
DeÁK Zsuzsanna,
Vass Imre,
Barber James,
Nixon Peter J.
Publication year - 1997
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1997.00731.x
Subject(s) - mutant , photosystem ii , thylakoid , plastoquinone , phycobilisome , missense mutation , biochemistry , biology , biophysics , chemistry , chlorophyll fluorescence , synechocystis , photosynthesis , microbiology and biotechnology , cyanobacteria , genetics , chloroplast , mutation , gene , bacteria
Two missense mutants, A263P and S264P, and a deletion mutant des‐Ala263, Ser264, have been constructed in the D1 protein of the cyanobacterium Syneclzocystis sp PCC 6803. All were expected to induce a significant conformational change in the Q B ‐binding region of photosystem II (PSII). Although the des‐Ala263, Ser264‐D1 mutant accumulated some D1 protein in the thylakoid membrane it was unable to grow photoautotrophically or evolve oxygen. Thermoluminescence and chlorophyll fluorescence studies confirmed that this deletion mutant did not show any functional PSII activity. In contrast, [S264P]D1 was able to grow photoautotrophically and give light‐saturated rates of oxygen evolution at 60% of the rate of the wild‐type control strain, TC31. The A263P missense mutant was also able to evolve oxygen at 50% of TC31 rates although it did not readily grow photoautotrophically. Thermoluminescence, flash oxygen yield and chlorophyll fluorescence measurements indicated that in both missense mutants electron transfer from Q A to Q B was significantly impaired in dark adapted cells. However, Q A to Q B electron transfer could be photoactivated in the mutants by background illumination. Both the A263P and S264P mutants also showed an increase in resistance to the s ‐triazine family of herbicides although this feature did not hold for the phenolic herbicide, ioxynil. Of particular interest was that the two missense mutants, especially S264P, possessed a slower rate of turnover of the D1 protein compared with TC31 and in vivo contained detectable levels of a 41‐kDa adduct consisting of D1 and the α subunit of cytochrotne B 559 . When protein synthesis was blocked by the addition of lincomycin, D1 degradation was again slower in S264P than TC31. The results are discussed in terms of structural changes in the Q B ‐binding region which affect herbicide and plastoquinone binding and perturb the normal regulatory factors that control the degradation of the D1 protein and its synchronisation with the synthesis of a replacement D1 protein.