PARENT SESSION
Posters P6B Photosynthetic acclimation: Mechanisms and gene expression. Abstracts (531-578)

Transcriptional profiles and structural models of the Synechocystis sp. PCC 6803 Deg proteases. Tove Jansén^*,1, Heidi Kidron², Hanna Taipaleenmäki¹, Tiina Salminen², Pirkko Mäenpää¹, ¹ 1Department of Biology, University of Turku, FIN-20014 Turku, Finland² Department of Biochemistry and Pharmacy, Åbo Akademi University, FIN-20521 Turku, Finland

ABSTRACT- Protein turnover is a vital process for all living organisms. This task is completed by the cellular protease complement. The Deg serine endopeptidases are wide spread among different organisms. In plants and cyanobacteria the Deg proteases have been addressed a role in photosystem II, specifically in turnover of photodamaged D1 protein, product of the psbA gene family. The Synechocystis 6803 genome harbours a deg gene family consisting of three members, htrA (slr 1204), hhoA (sll 1679) and hhoB (sll1427), the cellular roles and substrates of which are currently unknown. We studied Synechocystis 6803 Deg gene family members both at levels of gene transcription and protein structure to reveal details of the possible roles of the Deg proteases in D1 protein turnover. The responsiveness of Synechocystis 6803 htrA, hhoA and hhoB gene transcription to various environmental conditions including light, temperature, salinity and growth mode was monitored by northern blotting. The results revealed that the transcription of the deg genes is differentially regulated, supporting a view of distinct roles of Degs in Synechocystis 6803 cellular processes. Additionally, the overall transcriptional activation of the psbA2 gene is not fully synchronized with the deg genes, shown by the various environmental conditions tested. The oligomerisation state as well as the three dimensional structure of the Synechocystis 6803 Deg proteases were predicted based on an amino acid sequence alignment and comparison of the crystal structures from human, Escherichia coli and Thermotoga maritima. Results from these comparisons show that the structures of the Synechocystis 6803 Degs resemble more closer the Thermotoga maritima Deg structure than the Escherichia coli one. Moreover, the structures of the LA-loops hints towards a homotrimeric form of the Synechocystis 6803 Deg proteases.

KEY WORDS: Deg proteases, PSII, Synechocystis 6803, D1 protein