Expression, purification, and characterization of uracil phosphoribosyltransferase from Toxoplasma gondii

The coding region derived from a full-length CDNA spanning the uracil phosphoribosyltransferase (UPRT) gene of Toxoplasma gondii has been ligated into a bacterial expression vector and overexpressed in E. coli. Recombinant UPRT protein migrated with a molecular mass of 27 kDa on SDS polyacrylamide gels and was purified to homogeneity by conventional protein purification techniques. In solution, UPRT behaved as a monomer and exhibited K(m)app values of 3.5 microM for uracil and 243 microM for phosphoribosylpyrophosphate, respectively. Other naturally occurring pyrimidine or purine bases were not recognized as substrates. [14C]Uracil phosphoribosylation was inhibited by 5-fluorouracil with a Ki value of 25 microM and was not activated by GTP. Ample quantities of recombinant enzyme are now available for biochemical and structural studies, facilitating evaluation of UPRT as a possible therapeutic target.