An ATP-grasp family that is present both as catalytically active and inactive versions. Contextual analysis suggests that it functions in a distinct peptide synthesis/modification system that additionally contains a transglutaminase, an NTN-hydrolase, the Alpha-E domain, and a transglutaminase fused N-terminal to a circularly permuted COOH-NH2 ligase. The inactive forms are often fused N-terminal to the Alpha-E domain [1].

1: Amidoligases with ATP-grasp, glutamine synthetase-like and acetyltransferase-like domains: synthesis of novel metabolites and peptide modifications of proteins. Iyer LM, Abhiman S, Maxwell Burroughs A, Aravind L; Mol Biosyst. 2009;5:1636-1660. PMID:20023723