Escherichia coli Malic enzymes: two isoforms with substantial differences in kinetic properties, metabolic regulation and structure

BOLOGNA, F.; ANDREO, CS; MARIA FABIANA DRINCOVICH

JOURNAL OF BACTERIOLOGY

AMER SOC MICROBIOLOGY

Año: 2007 vol. 189 p. 5937 - 5946

0021-9193

Malic enzymes (MEs) catalyze the oxidative decarboxylation of malate in the presence of a divalent metal ion. In eukaryotes, well-conserved cytoplasmic, mitochondrial and plastidic MEs have been characterized. On the other hand, distinct groups can be detected among prokaryotic MEs, which are more diverse in structure and less characterized than their eukaryotic counterparts. In Escherichia coli, two genes with high degree of homology to ME can be detected: sfcA and maeB. MaeB possesses a multimodular structure: the N-terminal extension shows homology to ME while the C-terminal to phosphotransacetylases (PTAs). In the present work, a detailed characterization of the products from E. coli sfcA and maeB was performed. Results indicate that both ME exhibit relevant kinetic, regulatory and structural differences. SfcA is a NAD(P)-ME while MaeB a NADP-specific ME highly regulated by key metabolites. Characterization of truncated versions of MaeB indicated that the PTA-domain is not essential for the ME-reaction. Nevertheless, truncated MaeB without the PTA domain, losses most of its metabolic ME modulation and its native oligomeric state. Thus, the association of the two structural domains in MaeB seems to facilitate metabolic control of the enzyme. Although the PTA domain in MaeB is highly similar to domains of proteins with PTA activity, MaeB and its PTA domain do not exhibit PTA activity. Determination of the distinct properties of recombinant products from sfcA and maeB performed in the present work will help in the future to clarify the roles of MEs in prokaryotic metabolism