InterPro domain: IPR000544

Lipoate-protein ligase B [ 1 ] (gene lipB), alternatively known as octanoyltransferase ( 2.3.1.181 ) is an enzyme that creates an amide linkage that joins the free carboxyl group of lipoic acid to the epsilon-amino group of a specific lysine residue in lipoate-dependent enzymes.

Lipoyl(octanoyl) transferase catalyses the first committed step in the biosynthesis of lipoyl cofactor. The lipoyl cofactor is essential for the function of several key enzymes involved in oxidative metabolism, as it converts apoprotein into the biologically active holoprotein. Examples of such lipoylated proteins include pyruvate dehydrogenase (E2 domain), 2-oxoglutarate dehydrogenase (E2 domain), the branched-chain 2-oxoacid dehydrogenases and the glycine cleavage system (H protein) [ 2 ]. Lipoyl-ACP can also act as a substrate [ 3 ] although octanoyl-ACP is likely to be the true substrate [ 4 ]. The other enzyme involved in the biosynthesis of lipoyl cofactor is 2.8.1.8 , lipoyl synthase. An alternative lipoylation pathway involves 2.7.7.63 , lipoate-protein ligase, which can lipoylate apoproteins using exogenous lipoic acid (or its analogues).

Such an enzyme has also been found in fungi [ 5 ], where it is located in the mitochondria. It also seems to exist in plants [ 6 ] and is encoded in the chloroplast genome of the red alga Cyanidium caldarium [ 7 ].

1. Lipoic acid metabolism in Escherichia coli: the lplA and lipB genes define redundant pathways for ligation of lipoyl groups to apoprotein. J. Bacteriol. 177, 1-10
2. Lipoic acid metabolism in Escherichia coli: isolation of null mutants defective in lipoic acid biosynthesis, molecular cloning and characterization of the E. coli lip locus, and identification of the lipoylated protein of the glycine cleavage system. J. Bacteriol. 173, 6411-20
3. Assembly of the covalent linkage between lipoic acid and its cognate enzymes. Chem. Biol. 10, 1293-302
4. Swinging arms and swinging domains in multifunctional enzymes: catalytic machines for multistep reactions. Annu. Rev. Biochem. 69, 961-1004
5. Cloning and characterization of the lipoyl-protein ligase gene LIPB from the yeast Kluyveromyces lactis: synergistic respiratory deficiency due to mutations in LIPB and mitochondrial F1-ATPase subunits. Mol. Gen. Genet. 255, 341-9
6. Lipoic acid metabolism in Arabidopsis thaliana: cloning and characterization of a cDNA encoding lipoyltransferase. Plant Cell Physiol. 42, 650-6
7. The structure and gene repertoire of an ancient red algal plastid genome. J. Mol. Evol. 51, 382-90