Poster: Photosynthesis

Abs # 334: Physiological Role of CP12 for Regulation of the Calvin Cycle in Synechococcus PCC 7942

Presenter:	Tamoi, Masahiro , tamoi@nara.kindai.ac.jp
Authors	Tamoi, Masahiro  (A)   Takashi, Miyazaki  (A)   Tamo, Fukamizo  (A)   Shigeru, shigeoka  (A)
Affiliations:	(A): Kinki University

We reported previously that thiol-modulated enzymes in the Calvin cycle are not regulated by a ferredoxin/thioredoxin system (FTS) in cyanobacteria and lack potential redox-sensitive Cys involved in the FTS. The occurrence of the gene encoding CP12 in cyanobacterial cells suggests the possibility that the CP12 protein might regulate the activities of PRK and GAPDH by the reversible dissociation of PRK/CP12/GAPDH complex mediated by NADP(H)/NAD(H). The concentrations of NAD(H) and NADP(H) in Synechococcus PCC7942 cells under dark condition were 128 mM and 483 mM, respectively. The size exclusion chromatography and the immunoblot analysis using crude extracts of S. 7942 showed the existence of a 520-kDa PRK/CP12/GAPDH complex in the presence of 128 mM NAD⁺ and 483 mM NADPH. Under light condition, the concentrations of NAD(H) and NADP(H) in the cells were 100 mM and 649 mM, respectively, and the complexes were found to be dissociated in the crude extracts. These data suggest that the reversible dissociation of PRK/CP12/GAPDH complex is mediated by the change of NADP(H):NAD(H) ratio under light/dark conditions. The CP12 from higher plants, eukaryotic algae, and S. 6803 contained four Cys residues essential for the formation of two peptide loops. The N-terminal peptide loop was associated with PRK, while the C-terminal loop was with GAPDH. Interestingly, S. 7942 CP12 lacked the two Cys residues involved in the formation of the N-terminal loop. We constructed the CP12 mutant that changed Cys61 and Cys70 to Ser involved in the formation of C-terminal loop. This mutant CP12 protein could interact with PRK, but not with GAPDH, suggesting that the N-terminal region of CP12 is associated with PRK in spite of the absence of two Cys residues.