Acetyl-CoA carboxylase isoforms: Polymerization and formation of multi- protein complexes

Mammalian acetyl-CoA carboxylase (ACC) isoforms, ACC-1 and ACC-2, catalyze the formation of malonyl-CoA, a substrate for fatty acid synthesis and fatty acyl chain elongation, and a potent inhibitor of beta-oxidation. Based on the phenotype of knockout mice, ACC contributes significantly to overall body energy metabolism and is a potential drug target for the treatment of obesity and type II diabetes. Highly-purified ACC-1 undergoes a dramatic increase in mass following treatment with allosteric activators such as citrate, apparently due to linear polymerization of ACC dimers. The current studies were undertaken to explore (a) the extent to which ACC-2 undergoes polymerization and (b) to investigate whether other cellular proteins associate with and perhaps regulate the polymerization process. Size exclusion chromatography and sucrose gradient sedimentation studies show that ACC-2 undergoes very modest changes in molecular size upon allosteric activation, although the extent of polymerization of ACC-2 is enhanced in the presence of ACC-1. Isolation of the largest molecular forms of ACC, followed by mass spectrometry analysis, reveals that ACC "polymers" are multi-protein complexes. The proteins most reliably detected in ACC polymer fractions include tubulin, actin, fatty acid synthase, and heat shock proteins. The significance of the additional components of ACC complexes is evaluated from effects on the kinetics of the ACC reaction and of the polymerization process, as well as by cellular colocalization using fluorescence microscopy and co-immunoprecipitation studies. [ABSTRACT FROM AUTHOR]