BCCP

Biotin carboxyl carrier protein, abbreviated BCCP, is a subunit of biotin-dependent carboxylases, most notably acetyl-CoA carboxylase (ACCase). In bacteria and plants, ACCase is a multi-enzyme complex comprising a biotin carboxylase (BC), the BCCP, and a carboxyltransferase (CT). The BCCP carries the biotin prosthetic group, covalently attached to a highly conserved lysine, and functions as a swinging arm that transfers carboxyl groups between BC and CT during catalysis.

Biotinylation of BCCP is performed by biotin protein ligases: BirA in bacteria and holocarboxylase synthetase in eukaryotes. The biotinylated lysine is embedded in a short, conserved motif; the surrounding sequence and the protein’s structure allow the biotin to extend outward for carboxyl transfer. In bacteria, accB encodes BCCP and is commonly found in the acetyl-CoA carboxylase operon; in plants, BCCP domains are targeted to plastids as part of a single large ACCase complex.

Functionally, BCCP is essential for fatty acid biosynthesis because malonyl-CoA produced by ACCase serves as the building block for chain elongation. Without properly biotinylated BCCP, carboxylation does not proceed efficiently. The protein is conserved across bacteria and plastids and is a focus of studies in metabolism, structural biology, and metabolic engineering.

From a practical perspective, because many bacteria require ACCase activity for growth, BCCP and its biotinylation pathway are explored as potential antimicrobial targets. In biotechnology, engineering BCCP-containing ACCase systems can influence fatty acid production and carbon flux in microbial hosts and plants.