ANALYSES OF THE INTERACTION OF SUBUNITS OF NADP MALIC ENZYMES OF MAIZE

MARIANA SAIGO; MARÍA ALEJANDRA ROMERO; MARÍA FABIANA DRINCOVICH; CARLOS S. ANDREO

San Miguel de Tucumán

Congreso; Sociedad Argentina de Investigación en Bioquímica y Biología Molecular. XLV Reunión Anual; 2009

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Maize NADP-ME protein family has long being studied due to the essential role of one of the isoforms in carbon fixation (ZmME1). Even though the sequences in maize are well conserved, the photosynthetic isoform (ZmME1) is more closely related to a plastidic enzyme associated with housekeeping functions (ZmME2). Both isoforms have been extensively compared with regard to their kinetics and structural features. Besides the kinetic parameters, the oligomeric states also differ, while ZmME1 aggregates in the form of tetramers, ZmME2 remains as dimers in solution. Artificially generated chimerical structures allowed us to identify a region that strongly affects the quaternary structure of these enzymes. Moreover, we identified in silico some residues candidates to be involved in the assembly and stabilization of the tetramer. The aim of this work was to study the contribution of these residues to the basic kinetic parameters and the quaternary structure. In this regard, we replaced five residues in ZmME2 by the analogs found in ZmME1 by site-directed mutagenesis. The modified proteins were characterized by kinetic analysis and migration in non-denaturing PAGE. The results show that some single replacements had little or no effects on the structure, while two residues had major effects which indicate their involvement in the dimer assembly.