Journal Article

Redox Regulation of Chloroplast Enzymes in <i>Galdieria sulphuraria</i> in View of Eukaryotic Evolution

Christine Oesterhelt, Susanne Klocke, Simone Holtgrefe, Vera Linke, Andreas P. M. Weber and Renate Scheibe

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 48, issue 9, pages 1359-1373
Published in print September 2007 | ISSN: 0032-0781
Published online September 2007 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcm108
Redox Regulation of Chloroplast Enzymes in Galdieria sulphuraria in View of Eukaryotic Evolution

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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.

Keywords: Chloroplast enzymes; Complex formation; CP12; Galdieria sulphuraria; Light/dark modulation; Molecular evolution

Journal Article.  8082 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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