Human purine nucleoside phosphorylase double mutant E201Q,N243D complexed with 2-fluoroadenine
[PNPH_HUMAN] Defects in PNP are the cause of purine nucleoside phosphorylase deficiency (PNPD) [MIM:613179]. It leads to a severe T-cell immunodeficiency with neurologic disorder in children.  
[PNPH_HUMAN] The purine nucleoside phosphorylases catalyze the phosphorolytic breakdown of the N-glycosidic bond in the beta-(deoxy)ribonucleoside molecules, with the formation of the corresponding free purine bases and pentose-1-phosphate.
Publication Abstract from PubMed
A double mutant of human purine nucleoside phosphorylase (hDM) with the amino acid mutations Glu201Gln:Asn243Asp cleaves adenosine-based prodrugs to their corresponding cytotoxic drugs. When fused to an anti-tumor targeting component, hDM is targeted to tumor cells, where it effectively catalyzes phosphorolysis of the prodrug, 2-fluoro-2'-deoxyadenosine (F-dAdo) to the cytotoxic drug, 2-fluoroadenine (F-Ade). This cytotoxicity should be restricted only to the tumor microenvironment, because the endogenously expressed wild type enzyme cannot use adenosine-based prodrugs as substrates. To gain insight into the interaction of hDM with F-dAdo, we have determined the crystal structures of hDM with F-dAdo and F-Ade. The structures reveal that despite the two mutations, the overall fold of hDM is nearly identical to the wild type enzyme. Importantly, the residues Gln201 and Asp243 introduced by the mutation form hydrogen bond contacts with F-dAdo that result in its binding and catalysis. Comparison of substrate and product complexes suggest that the side chains of Gln201 and Asp243 as well as the purine base rotate during catalysis possibly facilitating cleavage of the glycosidic bond. The two structures suggest why hDM, unlike the wild-type enzyme, can utilize F-dAdo as substrate. More importantly, they provide a critical foundation for further optimization of cleavage of adenosine-based prodrugs, such as F-dAdo by mutants of human purine nucleoside phosphorylase.
Structure of a mutant human purine nucleoside phosphorylase with the prodrug, 2-fluoro-2'-deoxyadenosine and the cytotoxic drug, 2-fluoroadenine.,Afshar S, Sawaya MR, Morrison SL Protein Sci. 2009 May;18(5):1107-14. PMID:19388075
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.