Asparaginases (amidohydrolases, E.C. 3.5.1.1) are dimeric or tetrameric enzymes that catalyze the hydrolysis of asparagine to aspartic acid and ammonia. In bacteria, there are two classes of amidohydrolases, one highly specific for asparagine and localized to the periplasm (type II L-asparaginase), and a second (asparaginase- glutaminase) present in the cytosol (type I L-asparaginase) that hydrolyzes both asparagine and glutamine with similar specificities and has a lower affinity for its substrate. Bacterial L-asparaginases (type II) are potent antileukemic agents and have been used in the treatment of acute lymphoblastic leukemia (ALL). A conserved threonine residue is thought to supply the nucleophile hydroxy-group that attacks the amide bond. Many bacterial L-asparaginases have both L-asparagine and L-glutamine hydrolysis activities, to a different degree, and some of them are annotated as asparaginase/glutaminase. This wider family also includes a subunit of an archaeal Glu-tRNA amidotransferase.
Comment:Type II L-asparaginases are active as homotetramers; two intimate dimers each provide two active sites; the N-terminal domain of one subunit and the C-terminal domain of the second subunit each appear to contribute residues to each active site. GatD and type I L-asparaginase act as homodimers; for GatD both subunits appear to contribute residues to each active site, for type 1 L-asparaginase only one subunit appears to contribute residues at each active site.
Structure:1DJP: Pseudomonas glutaminase-asparaginase homodimer binds inhibitor in one of two active sites of the dimer
Structure:1ZQI: Pyrococcus abyssi GatD homodimer binds aspartic acid in one of two active sites (active site residues inferred via related family members), contacts at 4 A
Jiyao W et al.(2023). "The conserved domain database in 2023.",