InterPro domain: IPR042099

This superfamily comprises structural domains found at the N terminus of various ligases from the ANL superfamily. The name ANL derives from from three of the subfamilies - Acyl-CoA synthetases, the adenylation domains of the modular non-ribosomal peptide synthetases (NRPSs), and the luciferase enzymes. Members of this superfamily include luciferase, long chain fatty acid Co-A ligase, acetyl-CoA synthetase and various other closely-related synthetases as well as a plant auxin-responsive promoter family. These enzymes are involved in catalysing the initial adenylation of a carboxylate to form an acyl-AMP intermediate, followed by a second partial reaction, most commonly the formation of a thioester. These adenylating enzymes utilise a 140 degrees rotation of the C-terminal domain to adopt two distinct conformations that are used for the adenylation and thiolation reactions.

Thus, by using two different conformations of the C-terminal domain, these enzymes perform two distinct steps of catalysis.

Luciferases are composed of a large N-terminal domain and a smaller C-terminal domain, which form a cleft. The active site of these enzymes is located at the interface between these two domains, with most active site residues located in the N-terminal domain, and two lysine residues in the C-terminal domain. The N-terminal domain is involved in catalysis, and the C-terminal domain is essential for luciferase activation during the catalytic reaction [ 1 , 2 ].

The overall structure of the N-terminal domain has been characterised in a fatty acyl-CoA ligase in M. tuberculosis, FA and fatty acyl-AMP ligase FAAL28. The N-terminal domain of FA consists of three subdomains: subdomains A and B form alpha + beta topology, which pack together to form a five-layered alpha-beta-alpha-beta-alpha tertiary structure. The third subdomain C folds into a distorted beta-barrel topology. In FAAL28, the C-subdomain presents an insertion between beta-strands 1 and 2. A hydrophobic interaction was identified at the interface of insertion and N-terminal domain, and it was suggested to play a fundamental role in anchoring the insertion motif and arresting the acyl-CoA catalysis [ 3 ].

The Mycobacterium tuberculosis fatty acyl-CoA synthetase (ACS) FadD13 is a peripheral membrane protein essential for virulence and intracellular growth of the pathogen. FadD13 was identified to play a central role in lipid metabolism, and therefore would be a possible drug target. FadD13 comprises an N- and a C-terminal domain. The N-terminal domain folds into an alpha+beta topology and can be further divided into two subdomains. The CoA binding site in ACS proteins is formed in the junction between the domains upon a 140 degrees rotation of the C-terminal domain after the initial adenylation step [ 4 , 5 ].

1. Crystal structure of native and a mutant of Lampyris turkestanicus luciferase implicate in bioluminescence color shift. Biochim Biophys Acta 1834, 2729-35
2. Crystal structure of firefly luciferase in a second catalytic conformation supports a domain alternation mechanism. Biochemistry 51, 6493-5
3. Molecular basis of the functional divergence of fatty acyl-AMP ligase biosynthetic enzymes of Mycobacterium tuberculosis. J. Mol. Biol. 416, 221-38
4. The Mycobacterium tuberculosis very-long-chain fatty acyl-CoA synthetase: structural basis for housing lipid substrates longer than the enzyme. Structure 20, 1062-70
5. Structural and functional investigation of the intermolecular interaction between NRPS adenylation and carrier protein domains. Chem Biol 19, 188-98