CONICET | Buscador de Institutos y Recursos Humanos

Two highly similar plastidic NADP-malic enzymes (NADP-ME) are found in the C4 species maize (Zea mays); one exclusively expressed in the Bundle Sheath Cells (BSC) and involved in C4 photosynthesis (ZmC4-NADP-ME); and the other (ZmnonC4-NADP-ME) with housekeeping roles. In the present work, these two NADP-MEs were analyzed regarding their redox-dependent activity modulation. The results clearly show that ZmC4-NADP-ME is the only one modulated by redox status, and that its oxidation produces a conformational change limiting the catalytic process, although inducing higher-affinity binding of the substrates. The reversal of ZmC4-NADP-ME oxidation by chemical reductants suggests the presence of thiol groups able to form disulphide bonds. In order to identify the Cys residues involved in the activity modulation, site-directed mutagenesis and MALDI-TOF analysis of ZmC4-NADP-ME were performed. The results obtained allowed the identification of Cys192, Cys246 (not conserved in ZmnonC4-NADP-ME), Cys270 and Cys410 as directly or indirectly implicated in ZmC4-NADP-ME redox-modulation. These residues may be involved in forming disulphide bridge/s or in the modulation of the oxidation of critical residues. Overall, the results indicate that, besides having acquired a high level of expression and localization in BSC, ZmC4-NADP-ME displays a particular redox-modulation, which may be required to accomplish the C4 photosynthetic metabolism. Therefore, the present work could provide new insights into the regulatory mechanisms potentially involved in the recruitment of genes for the C4-pathway during evolutio