Central in oxygenic photosynthesis, the cytochrome b6f complex, couples electron transfer to proton translocation across the thylakoid membrane via its quinol:plastocyanin oxidoreductase activity, contributing to ATP formation. Cytochrome b6f complex differs from its respiratory homolog, the bc1 complex, by the presence of an additional heme, heme ci located within the quinone reduction site Qi and attached by a unique thioether bond. Mutants lacking heme ci show low accumulation of partially functional b6f complex and, hence, cannot grow phototrophically. This grounded a screen for suppressor mutations that would restore higher accumulation of b6f complexes whose function, even if compromised, would sustain phototrophic growth.The genetic suppressor approach undertook in Chlamydomonas reinhardtii during this PhD thesis led to the isolation and characterisation of the ftsh1-1 protease mutant (mutation R420C which should affect ATP hydrolysis). The mutant ftsh1-1 proved to be a versatile tool for the functional study of otherwise degraded proteins. The combination of genetic, biochemical, physiological and biophysical experiments demonstrated notably that: (i) a QiKO mutant, whose b6f complexes are devoid of both bh and ci hemes, can grow phototrophically despite a broken Q-cycle, (ii) the absence of covalently bound heme ci, in the Rccb2 mutant, triggers photosensivity enhanced in the presence of O2 supporting a role for heme ci in oxygen rich environment, (iii) FtsH is involved in the maintenance of the main photosynthetic complexes.
| Identifer | oai:union.ndltd.org:CCSD/oai:tel.archives-ouvertes.fr:tel-01057821 |
| Date | 08 July 2011 |
| Creators | Malnoë, Alizée |
| Publisher | Université Paris Sud - Paris XI |
| Source Sets | CCSD theses-EN-ligne, France |
| Language | English |
| Detected Language | English |
| Type | PhD thesis |
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