Structure and function of a single-chain, multi-domain long-chain acyl-CoA carboxylase

Biotin-dependent carboxylases are widely distributed in nature and have important functions in the metabolism of fatty acids, amino acids, carbohydrates, cholesterol and other compounds (1–6). Defective mutations in several of these enzymes have been linked to serious metabolic diseases in humans, and acetyl-CoA carboxylase (ACC) is a target for drug discovery against diabetes, cancer and other diseases (7–9). We report here the identification and biochemical, structural and functional characterizations of a novel single-chain (120 kD), multi-domain biotin-dependent carboxylase in bacteria. It has preference for long-chain acyl-CoA substrates, although it is also active toward short- and medium-chain acyl-CoAs, and we have named it long-chain acyl-CoA carboxylase (LCC). The holoenzyme is a homo-hexamer with molecular weight of 720 kD. The 3.0 Å crystal structure of Mycobacterium avium subspecies paratuberculosis LCC (MapLCC) holoenzyme revealed an architecture that is strikingly different compared to those of related biotin-dependent carboxylases (10,11). In addition, the domains of each monomer have no direct contacts with each other. They are instead extensively swapped in the holoenzyme, such that one cycle of catalysis involves the participation of four monomers. Functional studies in Pseudomonas aeruginosa suggest that the enzyme is involved in the utilization of selected carbon and nitrogen sources.