Crystal structures of Toxoplasma gondii uracil phosphoribosyltransferase reveal the atomic basis of pyrimidine discrimination and prodrug binding.

Journal Article (Journal Article)

Uracil phosphoribosyltransferase (UPRTase) catalyzes the transfer of a ribosyl phosphate group from alpha-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 A resolution), the UPRTase bound to its substrate, uracil (2.2 A resolution), its product, UMP (2.5 A resolution), and the prodrug, 5-fluorouracil (2.3 A 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 beta-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.

Full Text

Duke Authors

Cited Authors

  • Schumacher, MA; Carter, D; Scott, DM; Roos, DS; Ullman, B; Brennan, RG

Published Date

  • June 15, 1998

Published In

Volume / Issue

  • 17 / 12

Start / End Page

  • 3219 - 3232

PubMed ID

  • 9628859

Pubmed Central ID

  • PMC1170660

International Standard Serial Number (ISSN)

  • 0261-4189

Digital Object Identifier (DOI)

  • 10.1093/emboj/17.12.3219


  • eng

Conference Location

  • England