An uncharacterized alpha helical domain containing a highly conserved ER motif and typically found as a tandem duplication. Contextual analysis suggests that it functions in a distinct peptide synthesis/modification system comprising of a transglutaminase, a peptidase of the NTN-hydrolase superfamily, an active and inactive circularly permuted ATP-grasp domains and a transglutaminase fused N-terminal to a circularly permuted COOH-NH2 ligase 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