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- Title
Crystal structures of Toxoplasma gondii uracil phosphoribosyltransferase reveal the atomic basis of pyrimidine discrimination and prodrug binding.
- Authors
Schumacher, Maria A.; Carter, Darrick; Scott, Daniel M.; Roos, David S.; Ullman, Buddy; Brennan, Richard G.
- Abstract
Uracil phosphoribosyltransferase (UPRTase) catalyzes the transfer of a ribosyl phosphate group from α-D-5- phosphoribosyl-1-pyrophosphate to the N1 nitrogen of uracil. The UPRTase from the opportunistic pathogen Toxoplasma gondii is a rational target for antiparasitic drug design. To aid in structure-based drug design studies against toxoplasmosis, the crystal structures of the T.gondii apo UPRTase (1.93 &Aring: resolution), the UPRTase bound to its substrate, uracil (2.2 &Aring: resolution), its product, UMP (2.5 &Aring: resolution), and the prodrug, 5-fluorouracil (2.3 &Aring: resolution), have been determined. These structures reveal that UPRTase recognizes uracil through polypeptide backbone hydrogen bonds to the uracil exocyclic O2 and endocyclic N3 atoms and a backbone-water-exocyclic O4 oxygen hydrogen bond. This stereochemical arrangement and the architecture of the uracil-binding pocket reveal why cytosine and pyrimidines with exocyclic substituents at ring position 5 larger than fluorine, including thymine, cannot bind to the enzyme. Strikingly, the T.gondii UPRTase contains a 22 residue insertion within the conserved PRTase fold that forms an extended antiparallel β-arm. Leu92, at the tip of this arm, functions to cap the active site of its dimer mate, thereby inhibiting the escape of the substrate-binding water molecule.
- Subjects
TOXOPLASMA gondii; URACIL; CRYSTALLOGRAPHY; PYRIMIDINES; DRUG design; DRUGS; TOXOPLASMOSIS; COCCIDIOSIS
- Publication
EMBO Journal, 1998, Vol 17, Issue 12, p3219
- ISSN
0261-4189
- Publication type
Article
- DOI
10.1093/emboj/17.12.3219