InterPro domain: IPR004143

Biotin and lipoic acid are the covalently bound cofactors of variousmulticomponent enzyme complexes that catalyze key metabolic reactions. Inthese enzymes complexes, biotin and lipoic acid are attached via amide linkagethrough their carboxyl group and the epsilon-amino group of a specific lysineresidue of a protein module known respectively as the biotinyl and the lipoyldomain. Covalent attachment of biotin and lipoic acid tothese enzyme complexes occurs post-translationally, and it is mediated bybiotinylating and lipoylating protein enzymes, which specifically recognisethe biotinyl and lipoyl domains, ensuring their correct post-translationalmodification. Lipoylating and biotinylating enzymes are evolutionarily relatedprotein families containing a homologous catalytic module [ 1 ].

Amino acid sequence conservation between the catalytic modules of biotinylprotein ligases (BPLs) and lipoyl protein ligases (LPLs) is very low, andmainly affects residues that are important for the scaffold of the structure,such as those contributing to the hydrophobic core. Despite the poor overallsequence similarity, a single lysine residue is strictly conserved in all LPLand BPL sequences. This lysine residue is likely to bind specifically to thecarbonyl oxygen of the carboxyl group of biotin or at the end of the hydrogen-carbon tail of the lipoyl moiety [ 2 ]. The BPL/LPL catalytic domain contains aseven-stranded mixed beta-sheet on one side and four alpha-helices on theother side [ 2 ].

1. Lipoylating and biotinylating enzymes contain a homologous catalytic module. Protein Sci. 9, 1922-9
2. Crystal structures of biotin protein ligase from Pyrococcus horikoshii OT3 and its complexes: structural basis of biotin activation. J. Mol. Biol. 353, 322-33