Light-modulated NADP-malate dehydrogenases from mossfern and green algae: insights into evolution of the enzyme's regulation

Autor(en): Ocheretina, O
Haferkamp, I
Tellioglu, H
Scheibe, R 
Stichwörter: CDNA SEQUENCE; chloroplast; CLONING; DEPENDENT ACTIVATION; EXCHANGE; EXPRESSION; Genetics & Heredity; isoenzymes; LEAVES; METABOLITES; molecular evolution; MOTIF; PURIFICATION; redox regulation; SPINACH
Erscheinungsdatum: 2000
Journal: GENE
Volumen: 258
Ausgabe: 1-2
Startseite: 147
Seitenende: 154
Chloroplast NADP-dependent malate dehydrogenase is one of the best-studied light-regulated enzymes. In C3 plants, NADP-MDH is a part of the `malate valve' that controls the export of reducing equivalents in the form of malate to the cytosol. NADP-MDH is completely inactive in the dark and is activated in the light with reduced thioredoxin. Compared with its permanently active NAD-limited counterparts, NADP-MDH exhibits N- and C-terminal sequence extensions, each bearing one regulatory disulphide. Upon reduction of the C-terminal disulphide, the enzyme active site becomes accessible for the substrate. Reduction of the N-terminal disulphide promotes a conformational change advantageous for catalysis. To trace the evolutionary development of this intricate regulation mechanism, we isolated cDNA clones for NADP-MDH from the mossfern Selaginella and from two unicellular green algae. While the NADP-MDH sequence from Selaginella demonstrates the classic cysteine pattern of the higher plant enzyme, the sequences from the green algae are devoid of the N-terminal regulatory disulphide. Phylogenetic analysis of new sequences and of those available in the databases led to the conclusion that the chloroplast NADP-MDH and the cytosolic NAD-dependent form arose via duplication of an ancestral eubacterial gene, which preceded the separation of plant and animal lineages. Redox-sensitive NADP-MDH activity was detected only in the `green' plant lineage starting from the primitive prasinophytic algae but not in cyanobacteria, Cyanophora paradoxa, red algae and diatoms. The latter organisms therefore appear to utilize mechanisms other than the light-regulated `malate valve' to remove from plastids excessive electrons produced by photosynthesis. (C) 2000 Elsevier Science B.V. All rights reserved.
ISSN: 03781119
DOI: 10.1016/S0378-1119(00)00409-1

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