Reaction: [protein]-N6-(octanoyl)-L-lysine + an [Fe-S] cluster scaffold protein carrying a [4Fe-4S]2+ cluster + 2 S-adenosyl-L-methionine + 6 reduced [2Fe-2S] ferredoxin + 6 H+ = [protein]-N6-[(R)-dihydrolipoyl]-L-lysine + an [Fe-S] cluster scaffold protein + 2 sulfide + 4 Fe3+ + 2 L-methionine + 2 5'-deoxyadenosine + 6 oxidized [2Fe-2S] ferredoxin
Other name(s): lipA (gene name); LS; lipoate synthase; protein 6-N-(octanoyl)lysine:sulfur sulfurtransferase; protein N6-(octanoyl)lysine:sulfur sulfurtransferase; protein N6-(octanoyl)lysine:sulfur-(sulfur carrier) sulfurtransferase
Systematic name: [protein]-N6-(octanoyl)-L-lysine:an [Fe-S] cluster scaffold protein carrying a [4Fe-4S]2+ cluster sulfurtransferase
Comments: This enzyme catalyses the final step in the de-novo biosynthesis of the lipoyl cofactor, the attachment of two sulfhydryl groups to C6 and C8 of a pendant octanoyl chain. It is a member of the ‘AdoMet radical’ (radical SAM) family, all members of which produce the 5'-deoxyadenosin-5'-yl radical and methionine from AdoMet (S-adenosylmethionine) by the addition of an electron from an iron-sulfur centre. The enzyme contains two [4Fe-4S] clusters. The first cluster produces the radicals, which are converted into 5'-deoxyadenosine when they abstract hydrogen atoms from C6 and C8, respectively, leaving reactive radicals at these positions that interact with sulfur atoms within the second (auxiliary) cluster. Having donated two sulfur atoms, the auxiliary cluster is degraded during catalysis, but is regenerated immediately by the transfer of a new cluster from iron-sulfur cluster carrier proteins [8]. Lipoylation 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) [1,2]. An alternative lipoylation pathway involves EC 6.3.1.20, lipoate—protein ligase, which can lipoylate apoproteins using exogenous lipoic acid (or its analogues) [4].
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 189398-80-9
References:
1. Cicchillo, R.M. and Booker, S.J. Mechanistic investigations of lipoic acid biosynthesis in Escherichia coli: both sulfur atoms in lipoic acid are contributed by the same lipoyl synthase polypeptide. J. Am. Chem. Soc. 127 (2005) 2860-2861. [PMID: 15740115]
2. Vanden Boom, T.J., Reed, K.E. and Cronan, J.E., Jr. 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 (1991) 6411-6420. [PMID: 1655709]
3. Zhao, X., Miller, J.R., Jiang, Y., Marletta, M.A. and Cronan, J.E. Assembly of the covalent linkage between lipoic acid and its cognate enzymes. Chem. Biol. 10 (2003) 1293-1302. [PMID: 14700636]
4. Cicchillo, R.M., Iwig, D.F., Jones, A.D., Nesbitt, N.M., Baleanu-Gogonea, C., Souder, M.G., Tu, L. and Booker, S.J. Lipoyl synthase requires two equivalents of S-adenosyl-L-methionine to synthesize one equivalent of lipoic acid. Biochemistry 43 (2004) 6378-6386. [PMID: 15157071]
5. Jordan, S.W. and Cronan, J.E., Jr. A new metabolic link. The acyl carrier protein of lipid synthesis donates lipoic acid to the pyruvate dehydrogenase complex in Escherichia coli and mitochondria. J. Biol. Chem. 272 (1997) 17903-17906. [PMID: 9218413]
6. Miller, J.R., Busby, R.W., Jordan, S.W., Cheek, J., Henshaw, T.F., Ashley, G.W., Broderick, J.B., Cronan, J.E., Jr. and Marletta, M.A. Escherichia coli LipA is a lipoyl synthase: in vitro biosynthesis of lipoylated pyruvate dehydrogenase complex from octanoyl-acyl carrier protein. Biochemistry 39 (2000) 15166-15178. [PMID: 11106496]
7. Perham, R.N. Swinging arms and swinging domains in multifunctional enzymes: catalytic machines for multistep reactions. Annu. Rev. Biochem. 69 (2000) 961-1004. [PMID: 10966480]
8. McCarthy, E.L. and Booker, S.J. Destruction and reformation of an iron-sulfur cluster during catalysis by lipoyl synthase. Science 358 (2017) 373-377. [PMID: 29051382]