This is the N-terminal domain found in BL00235 present in Bacillus licheniformis. BL00235 is a ATP-grasp superfamily protein that catalyzes the formation of an alpha-peptide bond between two L-amino acids in an ATP-dependent manner. BL00235 has a highly restricted substrate specificity: the N-terminal substrate is confined to L-methionine an L-leucine, while the C-terminal substrates include small residues such as L-alanine, L-serine, L-threonine and L-cysteine [1].

1: The structure of L-amino-acid ligase from Bacillus licheniformis. Suzuki M, Takahashi Y, Noguchi A, Arai T, Yagasaki M, Kino K, Saito J; Acta Crystallogr D Biol Crystallogr. 2012;68:1535-1540. PMID:23090402