InterPro: IPR001249 Acetyl-CoA biotin carboxyl carrier

The proteins in this family are a component of the acetyl coenzyme A carboxylase complex (EC:6.4.1.2) and are involved in the first step in long-chain fatty acid synthesis. In plants this is usually located in the chloroplast. In the first step, biotin carboxylase catalyses the carboxylation of the carrier protein to form an intermediate. Next, the transcarboxylase complex transfers the carboxyl group from the intermediate to acetyl-CoA forming malonyl-CoA. This protein functions in the transfer of CO₂ from one site to another, the biotin binding site locates to the C-terminal of this protein. The biotin is specifically attached to a lysine residue in the sequence AMKM.

The structure of the C-terminal domain of the biotin carboxyl carrier (BCC) protein was shown to be a flattened beta-barrel structure comprising two four-stranded beta sheets interrupted by a structural loop forming a thumb structure. The biotinyl-lysine is located on a tight beta-turn on the opposite end of the molecule. The thumb structure has been shown to attached biotin, thus stabilising the structure.