Identification and bioinformatic analysis of the membrane proteins of synechocystis sp PCC 6803

Background: The membranes of Synechocystis sp. PCC 6803 play a central role in photosynthesis, respiration and other important metabolic pathways. Comprehensive identification of the membrane proteins is of importance for a better understanding of the diverse functions of its unique membrane structures. Up to date, approximately 900 known or predicted membrane proteins, consisting 24.5% of Synechocystis sp. PCC 6803 proteome, have been indentified by large-scale proteomic studies. Results: To resolve more membrane proteins on 2-D gels for mass spectrometry identification, we separated integral proteins from membrane associated proteins and collected them as the integral and peripheral fractions, respectively. In total, 95 proteins in the peripheral fraction and 29 proteins in the integral fraction were identified, including the 5 unique proteins that were not identified by any previous studies. Bioinformatic analysis revealed that the identified proteins can be functionally classified into 14 distinct groups according to the cellular functions annotated by Cyanobase, including the two largest groups hypothetical and unknown, and photosynthesis and respiration. Homology analysis indicates that the identified membrane proteins are more conserved than the rest of the proteome. Conclusion: The proteins identified in this study combined with other published proteomic data provide the most comprehensive Synechocystis proteome catalog, which will serve as a useful reference for further detailed studies to address protein functions through both traditional gene-by-gene and systems biology approaches.