The Calvin cycle in cyanobacteria is regulated by CP12 via the NAD(H)/NADP(H) ratio under light/dark conditions

Abstract

SummaryIn Synechococcus PCC7942 cells grown in the dark, the concentrations of NAD(H) and NADP(H) were 128 AE 2.5 and 483 AE 4.0 lM, respectively, while those in the cells under light conditions were 100 AE 5.0 and 649 AE 7.0 lM, respectively. Analysis of gel filtration indicated that the change of the ratio of NADP(H) to NAD(H) in cyanobacterial cells under light/dark conditions controls the reversible dissociation of the PRK/CP12/GAPDH complex (approximately 520 kDa) consisting of phosphoribulokinase (PRK), CP12, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). S. 7942 CP12 lacked the two Cys residues essential for formation of the N-terminal peptide loop in the CP12 of higher plants, but the N-terminal region of S. 7942 CP12 had the ability to be associated with PRK. The growth of mutant cells in which the CP12 gene was disrupted by a kanamycin resistance cartridge gene was almost the same as that of wild-type cells under continuous light conditions. However, under the light/dark cycle (12 h/12 h), the growth of CP12-disrupted mutant cells was significantly inhibited compared with that of wild-type cells. The mutant cells showed a decreased rate of O 2 consumption and an increased level of ribulose 1,5-bisphosphate compared with wild-type cells in the dark. These data suggest that under light and dark conditions, the oligomerization of CP12 with PRK and GAPDH regulates the activities of both enzymes and thus the carbon flow from the Calvin cycle to the oxidative pentose phosphate cycle.

Comparative Analysis of 126 Cyanobacterial Genomes Reveals Evidence of Functional Diversity Among Homologs of the Redox-Regulated CP12 Protein

“…These data provide strong evidence for a more diverse regulatory role for CP12 and CP12-like proteins in cyanobacteria, in either input signal or output activity, than previously thought. Direct support for this comes from analysis of an S. elongatus CP12-C knockout mutant that showed inhibited growth under dark/light conditions (Tamoi et al, 2005), suggesting that the CP12 variant (CP12-N/C) present in this organism could not compensate for the loss of CP12-C.…”

“…In eukaryotic organisms, CP12 is located in the chloroplast, where the only function thus far identified is in the regulation of the Calvin cycle in response to changes in light availability by reversibly binding glyceraldehyde-3-P dehydrogenase (GAPDH) and, subsequently, phosphoribulokinase (PRK; Wedel et al, 1997;Graciet et al, 2003aGraciet et al, , 2003bMarri et al, 2005aMarri et al, , 2008Erales et al, 2008a;Howard et al, 2008;Carmo-Silva et al, 2011). The formation of the GAPDH-PRK-CP12 complex inhibits GAPDH and PRK activity leading to down-regulation of the Calvin cycle; this has been demonstrated in plants, Chlamydomonas reinhardtii, and cyanobacteria (Wedel et al, 1997;Graciet et al, 2003a;Marri et al, 2005b;Tamoi et al, 2005). The GAPDH-PRK-CP12 complex dissociates under reducing conditions mediated by thioredoxin, thereby restoring GAPDH and PRK activity (Lebreton et al, 2003;Marri et al, 2005bMarri et al, , 2009Howard et al, 2008).…”

“…The importance of CP12 in cyanobacteria was demonstrated by analysis of an S. elongatus insertion mutant that showed, under both light and dark conditions, that the formation of the GAPDH-PRK-CP12 ternary complex regulated the activities of both enzymes and thus carbon flow from the Calvin cycle to the oxidative pentose phosphate cycle (Tamoi et al, 2005). More recently, it was shown that cyanophages of the marine picoplanktonic cyanobacteria genera Synechococcus and Prochlorococcus encode and express a CP12 protein similar to that of their hosts (Thompson et al, 2011).…”

“…In the cyanobacterium Synechococcus elongatus sp. PCC 7942 (hereafter S. elongatus), the N-terminal Cys pair is not required for PRK binding (Tamoi et al, 2005). In the green alga C. reinhardtii, CP12 and GAPDH have complex interactions centered on the Cys pairs.…”

Further characterization of the role of the mitochondrial high-mobility group box protein in the intracellular redox environment of Aspergillus nidulans

“…Mycelia were ground to powder under liquid nitrogen in a mortar. The measurement of NADP and NADPH was performed according to Tamoi et al (2005) using a 6800 UV/Vis spectrophotometer (Jenway). The levels of pyridine nucleotides were normalized to dry weight.…”