From C3 to C4: Evolution of maize NADP- Malic Enzyme

SAIGO M; FAHNENSTICH H; SAAVEDRA DD; MAURINO VG; DRINCOVICH MF; ANDREO CS

Alexandria

Congreso; BioVision Alexandria 2008. New Life Sciences: From Promises to Practice; 2008

The origin of C4 photosynthesis involved several morphological and biochemical adaptations. It is generally assumed that C4 specific enzymes arose by the acquisition of novel regulatory properties of duplicated copies of enzymes already present in the C3 ancestors. Maize and sorghum are C4 grasses in which a chloroplastic isoform of NADP-Malic enzyme (NADP-ME) decarboxylates malate to increase the concentration of CO2 in the surroundings of RuBisCO. These monocot plants along with rice, a C3 monocot, constitute a good model for the study of C4 evolution. Besides, maize and sorghum have two plastidic isoforms of NADP-ME, one involved in photosynthesis which is defined here as C4 type, whereas rice has only one isoform in this organelle. The aim of this work was to asses whether the previously reported kinetical and structural features that distinguish C4 from non-C4 isoforms in maize, can be found in sorghum and rice enzymes. First, the proteins were expressed in E. coli and purified by affinity chromatography. Kinetical parameters such as kcat, K substrates and substrate inhibition were assayed at pH7 and pH8. Additionally, the quaternary structure was determined by non denaturing electrophoresis. All the data obtained shows that the sequence-based classification of NADP-ME isoforms as C4 or non-C4 is in accordance with the kinetical and structural differences here presented.