Proteomic analysis of the heat shock and acclimation responses of cyanobacteria
The cyanobacterium Synechocystis sp. PCC 6803 is a model experimental organism for proteomic research because its entire genomic sequence is available and cyanobacteria have high adaptive potential towards a variety of environmental stresses. Heat shock characteristically induces expression of the heat shock proteins (Hsps) and photosynthetic organisms have demonstrated the ability to acclimatise their photosynthetic apparatus to milder elevated temperatures. In this study the proteomic methodology of two dimension gel electrophoresis and peptide mass fingerprinting mass spectrometry (PMF MS) was developed for the analysis of Synechocystis proteins. High resolution was attained with the application of narrow acidic pH range 'zoom' gels and of 192 individual soluble protein spots analysed via MALDI ToF, 105 were identified. A 2-D difference gel electrophoresis (2D DIGE) based proteomic approach has been applied to characterise the heat shock response in the soluble protein fraction and determine protein factors involved in the thermal acclimation of the thylakoid membrane and its associated photosynthetic machinery in Synechocystis. These analyses together with PMF MS for protein identification characterised 176 and 108 heat shock and heat acclimation responsive protein spots, respectively. In both analyses, molecular chaperones displayed the highest heat elevated level, demonstrating a dual role in stabilisation and refolding of both soluble and membrane-bound proteins. Other proteins identified in the heat shock response included those involved in photosynthesis, carbon fixation, translation, amino acid biosynthesis and several hypothetical proteins. Proteins involved in heat acclimation of the thylakoid membrane included constituents of photosynthesis, respiration, hopene biosynthesis and several hypothetical proteins. Furthermore, a candidate heat sensor involved in the regulation of heat shock gene expression has been characterised through analysis of the heat shock response in a histidine kinase knock out mutant strain of Synechocystis, namely Мік34, which displays increased thermal tolerance. The gene product of hik34 has a possible dual role in both the suppression of hsp gene expression under normal growth temperature and enhancement under heat shock.