Photosynthetic growth despite a broken Q-cycle

Malnoë A, Wollman FA, de Vitry C, Rappaport F.

Résumé:

Central in respiration or photosynthesis, the cytochrome bc₁ and b₆f complexes are regarded as functionally similar quinol oxidoreductases. They both catalyse a redox loop, the Q-cycle, which couples electron and proton transfer. This loop involves a bifurcated electron transfer step considered as being mechanistically mandatory, making the Q-cycle indispensable for growth. Attempts to falsify this paradigm in the case of cytochrome bc₁ have failed. The rapid proteolytic degradation of b₆f complexes bearing mutations aimed at hindering the Q-cycle has precluded so far the experimental assessment of this model in the photosynthetic chain. Here we combine mutations in Chlamydomonas that inactivate the redox loop but preserve high accumulation levels of b₆f complexes. The oxidoreductase activity of these crippled complexes is sufficient to sustain photosynthetic growth, which demonstrates that the Q-cycle is dispensable for oxygenic photosynthesis.

Revue:

Nature Communications

Lien:

www.nature.com/ncomms/journal/v2/n5/full/ncomms1299.html