| Popis: |
The cyanobacterium Synechocystis sp. strain BO 8402, isolated from Lake Constance, lacks phycobilisomes but instead forms inclusion bodies containing remnants of phycobiliproteins. The inclusion bodies are surrounded by a proteinaceous capsule and contain alpha-phycocyanin and beta-phycocyanin, the rod linker polypeptide L35RPC and a novel blue-colored protein L55 with an apparent molecular mass of 55 kDa. An antibody raised against beta-phycocyanin showed a strong cross-reaction with L55. Mass spectrometry analysis of proteolytic peptides from L55 revealed mass identity to proteolytic peptides derived from L35RPC and beta-phycocyanin. However, analysis of the genome of strain BO 8402 revealed only one cpcBACE operon, encoding the apoproteins of beta-phycocyanin and alpha-phycocyanin, L35RPC and a subunit of the phycocyanin alpha subunit phycocyanobilin lyase, respectively. The gene structure, sequence and transcription of these genes were identical to that of a revertant strain, Synechocystis sp. strain BO 9201, which formed phycobilisomes and did not express L55. Based on these observations, we concluded that L55 did not derive from a particular gene or from a special form of mRNA-processing. We propose that L55 is formed by post-translational fusion of L35RPC and beta-phycocyanin. Cross-linking may stabilize the formation of the large paracrystalline phycocyanin aggregates unique to Synechocystis sp. strain BO 8402. |
