Molecular identification of three Arabidopsis thaliana mitochondrial dicarboxylate carrier isoforms: organ distribution, bacterial expression, reconstitution into liposomes and functional characterization
Résumé
Screening of the Arabidopsis thaliana genome revealed three potential homologs of mammalian and yeast mitochondrial dicarboxylate carriers designated as DIC1, DIC2 and DIC3, each belonging to the mitochondrial carrier protein family. Each DIC is broadly expressed at the organ level, with DIC1 being the more highly expressed isoform and DIC3 being expressed at very low levels. DICs 1-3 have been reported previously as uncoupling proteins, but direct transport assays with recombinant and reconstituted DIC proteins clearly demonstrate that their substrate specificity is unique to plants, showing the combined characteristics of the dicarboxylate carrier and oxaloacetate carrier in yeast. Indeed, the Arabidopsis DICs transported a wide-range of dicarboxylic acids including malate, oxaloacetate and succinate as well as phosphate, sulphate and thiosulphate at high rates, whereas 2-oxoglutarate revealed to be a very poor substrate. The role of these plant mitochondrial dicarboxylate carriers is discussed with respect to other known mitochondrial carrier family members including uncoupling proteins. It is proposed that plant DICs constitute the membrane component of several metabolic processes including the malate-oxaloacetate shuttle, the most important redox connection between mitochondria and the cytosol.
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