Acetyl-CoA carboxylase (ACC) catalyzes the biotin-dependent carboxylation of acetyl-CoA to produce malonyl-CoA. This is the first and the committed step in the biosynthesis of long-chain fatty acids. At the same time, a second isoform of ACC, ACC2, is associated with the mitochondrial membrane and produces malonyl-CoA that regulates fatty acid oxidation by potently inhibiting the carnitine palmitoyltransferases (CPT-Is).

Mice that are deficient in ACC2 have elevated fatty acid oxidation and reduced body fat content and body weight, despite consuming more food. Therefore, inhibitors against ACCs might be efficacious for the treatment of obesity and diabetes (metabolic syndrome).

ACCs are multi-subunit enzymes in prokaryotes, whereas most eukaryotic ACCs are multi-domain enzymes. The biotin carboxylase (BC) domain catalyzes the first step of the reaction: the carboxylation of the biotin prosthetic group that is covalently linked to the biotin carboxyl carrier protein (BCCP) domain. In the second step of the reaction, the carboxyltransferase (CT) domain catalyzes the transfer of the carboxyl group from (carboxy)biotin to acetyl-CoA.

Some commercial herbicides kill plants by inhibiting the CT domain of their plastid ACC and thereby shutting down fatty acid biosynthesis. More recently, CP-640186 has been reported by Pfizer as a potent inhibitor of both isoforms of mammalian ACCs. Other potent inhibitors of mammalian ACCs have also been reported, some with significant selectivity between the two isoforms.

Soraphen A, a macrocyclic polyketide natural product, is a nanomolar inhibitor of the BC domain of eukaryotic ACCs, but it has no activity against the bacterial BC subunits.

While structures of the E. coli BC and BCCP subunits had been reported, no structural information was available for the CT domain. The CT domain shares no recognizable amino acid sequence homology to other proteins in the database.

• The crystal structure of the CT domain of yeast ACC has been determined at 2.7A resolution.


• The structure contains two domains, which share the same backbone folds. This fold belongs to the crotonase/ClpP family of proteins, with a b-b-a superhelix.


• There are many insertions on the surface of the domain, which are important for the dimerization of this enzyme.


• The domain exists as dimers in solution, with the monomers arranged in a head-to-tail fashion.


• The active site of the enzyme is located at the dimer inteface. We have determined the binding mode of CoA to the enzyme.


• Commercial herbicides inhibit CT at the active site.


• The structure of the haloxyfop herbicide in complex with the CT domain has been determined at 2.7A resolution.


• The herbicide is bound near the active site, but its binding requires large conformational changes for several residues in the active site.


• Two residues that confer resistance to the herbicides when mutated in plant ACCs, equivalent to Leu1705 and Val1967 of yeast ACC, are in the haloxyfop binding site.


• The structure of yeast CT in complex with CP-640186 has been determined at 2.7A resolution.


• CP-640186 is bound in the putative biotin binding site of CT, and causes only minor conformational change in the enzyme.


• The compounds CoA, haloxyfop, and CP-640186 identify three distinct regions in the active site of CT that could be used for developing inhibitors.


• The structure of yeast BC in complex with soraphen A has been determined at 1.8A resolution.


• Soraphen A may inhibit BC with a novel mechanism, by inhibiting its dimerization.


• The binding site for soraphen A is unique to the eukaryotic BC domains, thereby explaining its specificity.


• Dimerization of the E. coli BC subunit was believed to be required for its activity. We have generated mutants in the dimer interface that remain monomeric at micromolar concentrations. These mutants are active catalytically, suggesting that dimerization is not absolutely required for activity.


• Soraphen A may stabilize a form of the BC domain that is incompatible with catalysis.

Publications from this project

• H. Zhang, Z. Yang, Y. Shen & L. Tong. (2003). Crystal structure of the carboxyltransferase domain of acetyl-coenzyme A carboxylase. Science, 299, 2064-2067. Reprint(PDF)
• H. Zhang, B. Tweel & L. Tong. (2004). Molecular basis for the inhibition of the carboxyltransferase domain of acetyl-coenzyme A carboxylase by haloxyfop and diclofop. Proc. Natl. Acad. Sci. USA, 101, 5910-5915. Reprint(PDF)
• H. Zhang, B. Tweel, J. Li & L. Tong. (2004). Crystal structure of the carboxyltransferase domain of acetyl-coenzyme A carboxylase in complex with CP-640186. Structure, 12, 1683-1691. Reprint(PDF)
• Y. Shen, S.L. Volrath, S.C. Weatherly, T.D. Elich & L. Tong. (2004). A mechanism for the potent inhibition of eukaryotic acetyl coenzyme A carboxylase by soraphen A, a macrocyclic polyketide natural product. Mol. Cell, 16, 881-891. Reprint(PDF)
• L. Tong. (2005). Acetyl-coenzyme A carboxylase: crucial metabolic enzyme and attractive target for drug discovery. Cell. Mol. Life Sci., 62, 1784-1803. Reprint(PDF)
• Y. Shen, C.-Y. Chou, G.-G. Chang & L. Tong. (2006). Is dimerization required for the catalytic activity of bacterial biotin carboxylase? Mol. Cell, 22, 807-818. Reprint(PDF)
• L. Tong & H.J. Harwood, Jr. (2006). Acetyl-coenzyme A carboxylases: versatile targets for drug discovery. J. Cell. Biochem., 99, 1476-1488. Reprint(PDF)
• Y. Shen & L. Tong. (2008). Structural evidence for direct interactions between the BRCT domains of human BRCA1 and a phospho-peptide from human ACC1. Biochem., 47, 5767-5773. Reprint(PDF)

Funding for this project

• NIH R01 DK67238