The structural mechanism of GTP stabilized oligomerization and catalytic activation of the Toxoplasma gondii uracil phosphoribosyltransferase.

Journal Article (Journal Article)

Uracil phosphoribosyltransferase (UPRT) is a member of a large family of salvage and biosynthetic enzymes, the phosphoribosyltransferases, and catalyzes the transfer of ribose 5-phosphate from alpha-d-5-phosphoribosyl-1-pyrophosphate (PRPP) to the N1 nitrogen of uracil. The UPRT from the opportunistic pathogen Toxoplasma gondii represents a promising target for rational drug design, because it can create intracellular, lethal nucleotides from subversive substrates. However, the development of such compounds requires a detailed understanding of the catalytic mechanism. Toward this end we determined the crystal structure of the T. gondii UPRT bound to uracil and cPRPP, a nonhydrolyzable PRPP analogue, to 2.5-A resolution. The structure suggests that the catalytic mechanism is substrate-assisted, and a tetramer would be the more active oligomeric form of the enzyme. Subsequent biochemical studies revealed that GTP binding, which has been suggested to play a role in catalysis by other UPRTs, causes a 6-fold activation of the T. gondii enzyme and strikingly stabilizes the tetramer form. The basis for stabilization was revealed in the 2.45-A resolution structure of the UPRT-GTP complex, whereby residues from three subunits contributed to GTP binding. Thus, our studies reveal an allosteric mechanism involving nucleotide stabilization of a more active, higher order oligomer. Such regulation of UPRT could play a role in the balance of purine and pyrimidine nucleotide pools in the cell.

Full Text

Duke Authors

Cited Authors

  • Schumacher, MA; Bashor, CJ; Song, MH; Otsu, K; Zhu, S; Parry, RJ; Ullman, B; Brennan, RG

Published Date

  • January 8, 2002

Published In

Volume / Issue

  • 99 / 1

Start / End Page

  • 78 - 83

PubMed ID

  • 11773618

Pubmed Central ID

  • PMC117517

International Standard Serial Number (ISSN)

  • 0027-8424

Digital Object Identifier (DOI)

  • 10.1073/pnas.012399599


  • eng

Conference Location

  • United States