An insight into the role of 9360FtsH protease in photoprotection in the cyanobacterium Synechococcus PCC7942

Abstract

The multisubunit complex of photosystem-II, present in thylakoid membranes of all oxygen evolving photosynthetic organisms has some unique features. It drives one of the most thermodynamically demanding reactions, the oxidation of water. Yet it turns over more rapidly than any other protein complex of the photosynthetic apparatus and its D1 core protein, binding the majority of electron transport cofactors, is the most frequently damaged subunit of all. The repair mechanism operating to restore photosystem II to its functional state requires proteolytic activity to degrade the photoinactivated D1 subunit before replacing it with a newly synthesized copy. In our model organism, the cyanobacterium Synechococcus 7942, we explored the possibility that an FtsH protease (JGI ID 637799360) plays an important role in the early stages of the repair cycle by subjecting the gene encoding it to insertional mutagenesis. The phenotype of the resulted mutant was subsequently compared to that of the wild type, as both types of cells were simultaneously assessed using various biochemical and biophysical techniques. The assay produced results correlating well with the present knowledge about the role of the particular protease in other model organisms such as Synechocystis 6803 and Arabidopsis thaliana and thus substantiated the significance of the protease in the repair cycle of photosystem II and yet proposed an evolutionary conserved role among oxygenic phototrophs. We identified a possible role in the degradation of functional photosystem II under stress conditions and its dynamics within thylakoid membranes since absence of this protease profoundly affects the diffusion of the complex in the membranes. Besides, computational analysis of FtsH proteins, present as multigene families in all oxygenic phototrophs, brought forth the discovery of a unique domain present in cyanobacterial peptidases. 2