ON THE REGULATION OF TRIOSE-PHOSPHATE METABOLISM BY PROTEIN PHOSPHORYLATION

PIATTONI, CLAUDIA V.; GUERRERO, SERGIO A.; IGLESIAS, ALBERTO A.

Puerto Madryn, Chubut, Argentina

Congreso; XLVI Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2010

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Posttranslational modifications, as protein phosphorylation, regulate different processes in plants. In this work we analyzed phosphorylation of two plant cytosolic Ga3P dehydrogenases: the phosphorylating (Ga3PDHase, EC 1.2.1.12), and the non-phosphorylating (np-Ga3PDHase, EC 1.2.1.9) enzymes; which respectively derive triose-P to the synthesis of ATP and NADH or NADPH. We found that, in wheat endosperm, a protein kinase from the SnRK1 family is involved in modification of both Ga3PDHases. Phosphorylation occurs on residues Ser404 (np-Ga3PDHase) and Ser205 (Ga3PDHase), which localize in respective conserved domains that were described as preferred sites for SnRK1 phosphorylation. We purified and characterized the wheat endosperm SnRK1 kinase. The enzyme required Mg2+ or Mn2+ (but not Ca2+) for activity and it was allosterically inhibited by nearly physiological concentrations of Rib5P and to a lesser extent by Fru1,6bisP and 3PGA. Glc6P (the main effector of spinach leaf SnRK) produced little or no effect. MALDI-TOF analysis evidenced that sucrose synthase copurified with SnRK1, the former also being a target of the kinase action. We hypothesize that phosphorylation of both Ga3PDHases by SnRK1 would occur within a mechanism (specific of heterotrophic tissues) that coordinates carbon metabolism during the stage of reserve carbohydrates accumulation in developing wheat seeds