Biotin carboxyl carrier protein (BCCP) refers to proteins containing a biotin attachment domain that carry biotin and carboxybiotin throughout the ATP-dependent carboxylation by biotin-dependent carboxylases. The biotin carboxyl carrier protein is an Acetyl CoA subunit that allows for Acetyl CoA to be catalyzed and converted to malonyl-CoA. More specifically, BCCP catalyzes the carboxylation of the carrier protein to form an intermediate. Then the carboxyl group is transferred by the transcacrboxylase to form the malonyl-CoA. This conversion is an essential step in the biosynthesis of fatty acids. In the case of E. coli Acetyl-CoA carboxylase, the BCCP is a separate protein known as accB (). On the other hand, in Haloferax mediterranei, propionyl-CoA carboxylase, the BCCP pccA () is fused with biotin carboxylase.
The biosynthesis of fatty acids in plants, such as triacylglycerol, is vital to the plant's overall health because it allows for accumulation of seed oil. The biosynthesis that is catalyzed by BCCP usually takes place in the chloroplast of plant cells. The biosynthesis performed by the BCCP protein allows for the transfer of CO within active sites of the cell.
The biotin carboxyl carrier protein carries approximately 1 mol of biotin per 22,000 g of protein.
There is not much research on BCCPs at the moment. However, a recent studyon plant genomics found that Brassica BCCPs might play a key role in abiotic and biotic stress responses. Meaning that these proteins may be relaying messages to the rest of the plant body after it has been exposed to extreme conditions that disrupt the plant's homeostasis.