Identification of domains implicated in tetramerization and malate inhibition of maize C4 NADP-MALIC enzyme by analysis of chimerical proteins

ENRIQUE DETARSIO; CLARISA ALVAREZ; MARIANA SAIGO; CARLOS ANDREO; MARÍA F. DRINCOVICH

Pinamar, Argentina

Congreso; Sociedad Argentina de Investigación en Bioquímica y Biología Molecular XLI Reunión Anual; 2005

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

C4 photosynthetic NADP-malic enzyme has evolved from non-C4 isoforms during evolution and gained unique kinetic and structural properties. In order to identify the domains responsible for the structural and kinetic differences between maize C4- and non-C4 NADP-ME several reciprocal enzyme chimeras between these isoforms were constructed and analysed. By this approach, a region between aminoacids 102 and 247 was found to be implicated in the oligomerization state, being responsible for the tetrameric state of the C4 NADP-ME. In this way, the strategy for oligomerization of these NADP-ME isoforms differs markedly from the one that is present in non-plant NADP-ME crystallized until present. On the other hand, the region from aminoacid 248 to the carboxyl terminal of the protein was implicated in the inhibition by high malate concentrations at pH 7.0 of the C4 isoform. The inhibition pattern of the C4-NADP-ME and some of the chimeras suggested an allosteric site responsible for such inhibition. Based on structural analysis, two sites are proposed as potential targets for malate allosteric binding. In this way, this inhibition may be important for the regulation of the C4 isoform in vivo; being fully active when photosynthesis is in progress.