E. coli malic enzymes: a NAD(P)-ME and a multimodular NADP-ME with dual enzymatic activity

BOLOGNA F,; CARLOS SANTIAGO ANDREO; DRINCOVICH MF,

Rosario

Congreso; XLII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular, SAIB; 2006

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Malic enzyme (ME) catalyses the oxidative decarboxylation of malate to yield pyruvate, CO2 and NAD(P)H. Distinct isoforms of ME are expressed in both prokaryotic and eukaryotic organisms, where they play diverse metabolic roles. By sequence homology, two isoforms of ME have been detected in E. coli genome: sfcA and maeB. Both genes present high degree of homology with ME from different sources, having the product of maeB an N-terminal region that presents homology with ME and a C-terminal region of approximately 320 amino acids, which shows homology to phosphotransacetylase enzymes (PTA). The aim of the present work was the cloning and expression of both enzymes and the products from the two regions composing MaeB. Complete and truncated proteins were purified and kinetically and structurally characterized. The product of the maeB N-terminal region retained ME activity, although the properties of this truncated enzyme were different from that of the complete maeB protein. The maeB protein as well as the product of the C-terminal region presented PTA activity. In this way maeB is a bifunctional enzyme which activities are reciprocally regulated. The results indicate that the two E. coli ME may fulfill different metabolic roles in vivo and that their activities are highly regulated by different key metabolic compounds