Fig. 5: Role of the YRE loop and arrangement of the glutaminase active site.

a This panel illustrates the hsNadE glutaminase domain with the glutaminase active site free of ligand in a complex with the synthetase active site fully occupied with the intermediate analog. b The glutaminase active site of tbNadE subunit D is occupied with glutamine in a complex with SFIs and PPi bound in the synthetase active site of the coupled subunit B. The YRE loop residues are shown in orange sticks in all complexes, the catalytic and substrate-binding residues are shown in green in hsNadE and purple in tbNadE. The glutamine substrate and water in the ammonia tunnel of the tbNadE complex are shown as a yellow stick and red sphere. c Overlay of the hsNadE and tbNadE–DON complexes (PDB code 3DLA). Distance of hydrogen bonding between (i) YRE loop’s glutamate and catalytic lysine and (ii) the glutamate and constriction 1’s tyrosine is shown as green (hsNadE) and gray (tbNadE) numbers. d–f The glutaminase active site of previously reported tbNadE structures bound to waters in the apo form (PDB code 3SDB) (d), with DON bound (dark purple stick, PDB code 3DLA) (e), and with glutamate bound (green stick, PDB code 3SYT (f).