Study of the structure-function relationship in maize NADP-malic enzyme

DETARSIO, E.; CLARISA ALVAREZ; SAIGO, MARIANA; MARIA FABIANA DRINCOVICH; ANDREO, CARLOS S

Photosynthesis. Energy from the Sun

Springer Publishing

Lugar: No Informado; Año: 2007; p. 841 - 844

NADP-malic enzyme catalyses the reversible oxidative decarboxylation of L-malate to yield carbon dioxide and pyruvate with the concomitant reduction of NADP.  Maize presents at least three isoforms of this enzyme, and the “photosynthetic isoform” is responsible for providing CO2 to the Calvin Cycle for carbon fixation. In this work, different aspects of the enzyme were studied by recombinant protein engineering. The site directed mutagenesis of the residues A392 and K435/6 indicated that these residues contribute to the specificity of NADP over NAD as substrate of the enzyme. The mutation of the conserved basic residues K255 and R237 showed that they are implicated in substrate binding and catalysis, probably acting as a base. In addition, four cysteine residues C192, C231, C246 and C270 were shown to affect the catalytic activity when mutated to alanine. The structural basis of the differences between the photosynthetic (C4) and non-photosynthetic (non-C4) isoform were studied by constructing and analyzing chimeras between these isoforms, which indicated that the region between residues 102 and 247 is necessary for tetramerization capacity of the photosynthetic isoform, and the region between residues 247 and C terminus is responsible for malate inhibition at pH 7.0.