Proteomics of Synechocystis sp strain PCC 6803 - Identification of periplasmic proteins in cells grown at low and high salt concentrations

Periplasmic proteins isolated by cold osmotic shock of Synechocystis sp. PC C 6803 cells were identified using 2D PAGE, MS and genome analysis. Most of the periplasmic proteins represent 'hypothetical proteins' with unknown fu nction. A number of proteases of different specificity, and several enzymes involved in cell wall biosynthesis were also found. In salt-adapted cells, six proteins were greatly enhanced and three proteins were newly induced. Most of the salt-enhanced proteins are involved in the alteration of cell w all structure of salt-adapted cells. The precursors of all 57 periplasmic p roteins identified have a signal peptide; 47 of them contain a typical Sec- dependent signal peptide, whereas 10 contain a putative twin-arginine signa l peptide.