Biotin Cofactor biochemistry
D-(+)-Biotin is a cofactorresponsible for carbon dioxidetransfer in several carboxylaseenzymes:
Methylcrotonyl-CoA carboxylase
Biotin is important in fatty acid synthesis, branched-chain amino acid catabolism, and gluconeogenesis. It covalently attaches to the epsilon-amino group of specific lysine residues in these carboxylases. This biotinylationreaction requires ATPand is catalyzed by holocarboxylase synthetase.[12]In bacteria, biotin is attached to biotin carboxyl carrier protein (BCCP) by biotin protein ligase (BirA in E. coli).[13]The attachment of biotin to various chemical sites, biotinylation, is used as an important laboratory technique to study various processes, including protein localization, protein interactions, DNAtranscription, and replication. Biotinidase itself is known to be able to biotinylate histone proteins,[14]but little biotin is found naturally attached to chromatin.
Biotin binds very tightly to the tetrameric protein avidin(also streptavidinand neutravidin), with a dissociation constantKd on the order of 10−15M, which is one of the strongest known protein-ligand interactions.[15]This is often used in different biotechnological applications. Until 2005, very harsh conditions were thought to be required to break the biotin-streptavidin bond.[16]
