Proteomic study of the peripheral proteins from thylakoid membranes of thecyanobacterium Synechocystis sp PCC 6803

Thylakoid membranes of cyanobacteria and plants contain enzymes that functi on in diverse metabolic reactions. Many of these enzymes and regulatory pro teins are associated with the membranes as peripheral proteins. To identify these proteins, we separated and identified the peripheral proteins of thy lakoid membranes of the cyanobacterium Synechocystis sp. PCC 6803. Trichlor oacetic acid (TCA)-acetone extraction was used to enrich samples with perip heral proteins and to remove integral membrane proteins. The proteins were separated by two-dimensional electrophoresis (2-DE) and identified by pepti de mass fingerprinting. More than 200 proteins were detected on the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gel that was stained with colloidal Coomassie blue. We analyzed 116 spots by peptide mas s fingerprinting and identified 78 spots that were derived from 51 genes. S ome proteins were found in multiple spots, indicating differential modifica tions resulting in charge differences. Therefore, a significant fraction of the peripheral proteins in thylakoid membranes is modified post-translatio nally. In our analysis, products of 17 hypothetical genes could be identifi ed in the peripheral protein fraction. Therefore, proteomic analysis is a p owerful tool to identify location of the products of hypothetical genes and to characterize complexity in gene expression due to post-translational mo difications.