Functional studies on the Deg/HtrA proteases of the cyanobacterium Synechocystis sp. PCC 6803
Christiane Funk, Department of Biochemistry

Organisms that perform oxygenic photosynthesis are subjected to inhibition of their photosynthetic function when exposed to excessive illumination. The main target of light stress is the oxygen-evolving Photosystem II (PSII) and its D1 reaction center protein. The degradation and replacement of photodamaged D1 protein by a functional copy represent an important repair mechanism of Photosystem II. In vitro studies revealed that a chloroplast Deg type serine protease performs the primary cleavage of photodamaged D1 protein in Arabidopsis thaliana (Haußühl, K., Andersson, B. & Adamska, I., 2001, EMBO J. 20, 713-722). The photosynthetic cyanobacterium Synechocystis sp. PCC6803 has three homologues to this DegP2 protease, called HhoA, HhoB and HtrA. Their role in D1 degradation in vivo is still under debate. After generating single mutants as well as a triple deletion mutant we now want to study the role of these proteases and also the mechanisms, Synechocystis 6803 uses to compensate for their loss. We will start taking the proteomic approach with DIGE-fluorescence staining. In the next step we will look at the metabolome of wild type compared to the mutants. After establishing the methods we will investigate different stress conditions (e.g. light/heat).