Characterization of malic enzyme and the regulation of its activity and metabolic engineering on lipid production

Nowadays, microbial lipids are employed as the feedstock for biodiesel production, which has attracted great attention across the whole world. Malic enzyme (ME) is a key enzyme regulating the lipid accumulation process in oleaginous microorganisms. It catalyzes the oxidative decarboxylation of L-malate to pyruvate and CO2 with concomitant reduction of NADP(+) to NADPH, supplying the reducing power for fatty acid biosynthesis. The extent of lipid accumulation in some fungi is identified to be controlled by ME acting as the sole source of NADPH. This review covers related research about molecular characterization and biochemical properties of MEs from various sources, and summarizes several possible modulators that affect ME activity during the lipid production process. If those harmful effects on ME activity throughout the lipid accumulation can be eliminated, more lipids can be produced. In addition, recent progress in overexpression of the ME gene for lipid biosynthesis is discussed. Quite a few successful stories in lipid overproduction by homologous or heterogenous overexpression of ME have occurred in some transformed microbial strains, indicating that ME is a promising target for gene transformation. However, the role of ME in the regulation of lipid biosynthesis is challenging in some cases.