Biochemical characterization of the biotin-dependent carboxylases, acetyl-CoA carboxylase and 3-methylcrotonyl-CoA carboxylase

cetyl-CoA Carboxylase (ACC) catalyzes the conversion of acetyl-CoA to malonyl-CoA. Dicot plants have a homomeric ACC (hmACC) located in the cytosol responsible for the generation of malonyl-CoA pools for fatty acid elongation and secondary metabolites such as isoprenoids. Dicots utilize a heteromeric ACC (htACC) consisting of four subunits which as a holo-htACC generate malonyl-CoA for de novo fatty acid biosynthesis in the plastid. All ACC contain three functional domains. Biotin carboxylase (BC) catalyzes the ATP dependent carboxylation of biotin while carboxyltransferase (CT) catalyzes the transfer of the carboxyl group from biotin to acetyl-CoA. A biotin carboxyl carrier protein (BCCP) contains the cofactor biotin that is covalently linked to a conserved lysine residue and mediates between both half reactions. Arabidopsis thaliana (Arabidopsis) htACC contains natural structural diversity. Two isoforms of BCCP have been identified (CAC1A, At5g16390 encodes BCCP1, CAC1B, At5g15530 encodes BCCP2). In addition to BCCP isoforms, RNA-editing within the plastome encoded ACCD (AtCg00500 encoding CTbeta) results in a serine to leucine point mutation at amino acid residue...