NADP-malate dehydrogenase from unicellular green algal Chlamydomonas reinhardtii. A first step toward redox regulation?

• Published in: Plant physiology (Bethesda) Vol. 137; no. 2; pp. 514 - 521
• Main Authors: Lemaire, S.D, Quesada, A, Merchan, F, Corral, J.M, Igeno, M.I, Keryer, E, Issakidis-Bourguet, E, Hirasawa, M, Knaff, D.B, Miginiac-Maslow, M
• Format: Journal Article
• Language: English
• Published: 2005
• Subjects: algae and seaweeds; amino acid sequences; Chlamydomonas reinhardtii; chloroplasts; malate dehydrogenase (NADP); molecular sequence data; plant proteins; redox potential; redox reactions; sequence alignment; structure-activity relationships; thioredoxin
• ISSN: 0032-0889; 1532-2548

The determinants of the thioredoxin (TRX)-dependent redox regulation of the chloroplastic NADP-malate dehydrogenase (NADP-MDH) from the eukaryotic green alga Chlamydomonas reinhardtii have been investigated using site-directed mutagenesis. The results indicate that a single C-terminal disulfide is responsible for this regulation. The redox midpoint potential of this disulfide is less negative than that of the higher plant enzyme. The regulation is of an all-or-nothing type, lacking the fine-tuning provided by the second N-terminal disulfide found only in NADP-MDH from higher plants. The decreased stability of specific cysteine/alanine mutants is consistent with the presence of a structural disulfide formed by two cysteine residues that are not involved in regulation of activity. Measurements of the ability of C. reinhardtii thioredoxin f (TRX f) to activate wild-type and site-directed mutants of sorghum (Sorghum vulgare) NADP-MDH suggest that the algal TRX f has a redox midpoint potential that is less negative than most those of higher plant TRXs f. These results are discussed from an evolutionary point of view.