The phycocyanin-associated rod linker proteins of the phycobilisome of Gloeobacter violaceus PCC 7421 contain unusually located rod-capping domains

Gloeobacter violaceus PCC 7421 is a unique cyanobacterium that has no thylakoids and whose genome has been sequenced Y. Nakamura, T. Kaneko, S. Sato, M. Mimuro, H. Miyashita, T. Tsuchiya, S. Sasamoto, A. Watanabe, K. Kawashima, Y. Kishida, C. Kiyokawa, M. Kohara, M. Matsumoto, A. Matsuno, N. Nakazaki, S. Shimpo, C. Takeuchi, M. Yamada, S. Tabata, Complete Genome Structure of Gloeobacter violaceus PCC 7421, a cyanobacterium that lacks thylakoids. DNA Research 10 (2003) 137-145]. Phycobilisomes of G. violaceus were isolated and analyzed by SDS-PAGE followed by N-terminal sequencing. Three rod-linker subunits (CpeC, CpeD and CpeE) were identified as predicted from the genome sequence. The cpcC1 and cpcC2 genes at order locus named (OLN) glr0950 and gll 3219 encoding phycocyanin-associated linker proteins from G. violaceus are 56 and 55 amino acids longer at the N-terminus than the open reading frame proposed in the genome. The two amino acid extensions showed a 66% identity to one another. Also, the N-terminal extensions of these sequences were similar to domains in both the rod-capping-linker protein CpcD2 and to the C-terminus domain of the phycoerythrin-associated linker protein CpeC. These domains are not only unusual in their N-terminal location, but are unusual in that they are more closely related in sequence similarity to the C-terminus domain of the phycoerythrin-associated linker, CpeC of G. violaceus, than to the C-terminus domain of phycocyanin-associated linker CpcC in other cyanobacteria. These linker proteins with unique special domains are indicators of the unusual structure of the phycobilisomes of G. violaceus.