Isolation and molecular characterization of the bifunctional hydroxymethyldihydropterin pyrophosphokinase-dihydropteroate synthase gene from Toxoplasma gondii

Tanya V. Pashley, Filippo Volpe, Mary Pudney, John E. Hyde, P. F G Sims, Chris J. Delves

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Toxoplasma gondii is an important cause of AIDS-related opportunistic infection, manifest as toxoplasmic encephalitis. The clinical treatment of choice is the synergistic combination of antifolate agents, pyrimethamine and sulphadiazine, of which the latter targets the parasite's dihydropteroate synthase (DHPS) activity. Here, we describe the isolation of the gene encoding this activity in T. gondii. The nucleotide sequence contains an open reading frame interrupted by five introns, which encodes a protein of 664 amino acids with an M(r) of 72991. Sequence analysis revealed that, in addition to DHPS, the predicted protein contains a second enzyme function, hydroxymethyldihydropterin pyrophosphokinase (PPPK). This enzyme immediately precedes DHPS in the folate biosynthetic pathway. The bifunctional arrangement of the T. gondii pppk-dhps gene is the same as that observed in the related protozoan parasite, Plasmodium falciparum, and confirms previous biochemical data that these activities were inseparable. Recently, specific mutations within conserved motifs of the DHPS gene of P. falciparum have been identified which give rise to sulphonamide drug resistance. Analysis of seven clinical isolates of T. gondii did not reveal any similar mutations in this limited sample of organisms that had been subjected to drug pressure.
    Original languageEnglish
    Pages (from-to)37-47
    Number of pages10
    JournalMolecular and biochemical parasitology
    Volume86
    Issue number1
    DOIs
    Publication statusPublished - 1997

    Keywords

    • antifolates
    • dihydropteroate synthase
    • drug resistance
    • hydroxymethyldihydropterin pyrophosphokinase
    • Toxoplasma gondii

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