title: Redox regulation of chloroplast enzymes in Galdieria sulphuraria in view of eukaryotic evolution.
abstract: Redox modulation is a general mechanism for enzyme regulation, particularly for the post-translational regulation of the Calvin cycle in chloroplasts of green plants. Although red algae and photosynthetic protists that harbor plastids of red algal origin contribute greatly to global carbon fixation, relatively little is known about post-translational regulation of chloroplast enzymes in this important group of photosynthetic eukaryotes. To address this question, we used biochemistry, phylogenetics and analysis of recently completed genome sequences. We studied the functionality of the chloroplast enzymes phosphoribulokinase (PRK, EC 2.7.1.19), NADP-dependent glyceraldehyde 3-phosphate dehydrogenase (NADP-GAPDH, GapA, EC 1.2.1.13), fructose 1,6-bisphosphatase (FBPase, EC 3.1.3.11) and glucose 6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49), as well as NADP-malate dehydrogenase (NADP-MDH, EC 1.1.1.37) in the unicellular red alga Galdieria sulphuraria (Galdieri) Merola. Despite high sequence similarity of G. sulphuraria proteins to those of other photosynthetic organisms, we found a number of distinct differences. Both PRK and GAPDH co-eluted with CP12 in a high molecular weight complex in the presence of oxidized glutathione, although Galdieria CP12 lacks the two cysteines essential for the formation of the N-terminal peptide loop present in higher plants. However, PRK inactivation upon complex formation turned out to be incomplete. G6PDH was redox modulated, but remained in its tetrameric form; FBPase was poorly redox regulated, despite conservation of the two redox-active cysteines. No indication for the presence of plastidic NADP-MDH (and other components of the malate valve) was found.
authors: Department of Plant Physiology, Institute for Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str 24-25, D-14476, Potsdam-Golm, Germany.
authors: Christine
authors: C
authors: Oesterhelt
authors: Susanne
authors: S
authors: Klocke
authors: Simone
authors: S
authors: Holtgrefe
authors: Vera
authors: V
authors: Linke
authors: Andreas P M
authors: AP
authors: Weber
authors: Renate
authors: R
authors: Scheibe
mesh_terms: D020418:Algal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D002736:Chloroplasts / Q000201:enzymology*; D004798:Enzymes / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D024601:Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+) / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050538:Malate Dehydrogenase (NADP+) / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010944:Plants / Q000201:enzymology / Q000235:genetics; D000461:Rhodophyta / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D020418:Algal Proteins; D004798:Enzymes; D010940:Plant Proteins; D050538:Malate Dehydrogenase (NADP+); D024601:Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+); D017853:Phosphotransferases (Alcohol Group Acceptor); C022390:phosphoribulokinase