Currently, there are no structures of NRPS A domains that activate anthranilate (Ant), but two CoA ligases bound to Ant-AMP are available, AuaEII involved in aurachin biosynthesis and PqsA from Pseudomonas quinolone signal (PQS) synthesis. CoA-ligases do not maintain the same substrate selectivity codes as NRPS A domains, but the structural report of AuaEII listed 19 residues that were critical for binding the various chemical moieties of Ant-AMP (SFTFASEADGIGCTHIDRK). Only eight of these residues were required for anthranilate interactions (F220, T221, F222, A293, G318, C319, H324 and I325), with F222, A293, H324 and I325 participating directly in aryl interactions (AuaEII numbering) (Figure ). Regarding PqsA, there were four anthranilate-interacting residues noted in the PqsA structure (Y211, A278, G302 and H308, PqsA numbering) (Figure ), as well as several others in its 15 residue binding pocket (QYAGSPDGIGTGHDR). In PqsA, the α-amino group of Ant was coordinated differently than in AuaEII, utilizing a water molecule to bridge Q162 and the carbonyl of G307. With AuaEII, by contrast, a direct hydrogen bond from T221 (corresponding to G210 in PqsA) was found to bind the α-amino group, indicating that there are two different modes of α-amino recognition in Ant-CoA ligases.