Figure 1

Schematic diagram showing the reaction catalyzed by the biotin protein ligase (BPL) and the general mechanism shared by the biotin-dependent carboxylases. Biotin (in green) is first activated to biotinyl-5'-AMP by BPL, then it is transferred by the same enzyme to a biotin carboxyl carrier protein (BCCP). Biotin-dependent carboxylases (in purple) are made up of a biotin carboxylase domain (BC), a carboxyl transferase domain (CT) and the BCCP. The BC domain fixes a CO₂ molecule to the BCCP-bound biotin and then the CT component binds the carboxyl group to its specific substrate.