IMP dehydrogenase from the protozoan parasite Toxoplasma gondii

William Sullivan, Stacy E. Dixon, Catherine Li, Boris Striepen, Sherry Queener

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

The opportunistic apicomplexan parasite Toxoplasma gondii damages fetuses in utero and threatens immunocompromised individuals. The toxicity associated with standard antitoxoplasmal therapies, which target the folate pathway, underscores the importance of examining alternative pharmacological strategies. Parasitic protozoa cannot synthesize purines de novo; consequently, targeting purine salvage enzymes is a plausible pharmacological strategy. Several enzymes critical to purine metabolism have been studied in T. gondii, but IMP dehydrogenase (IMPDH), which catalyzes the conversion of IMP to XMP, has yet to be characterized. Thus, we have cloned the gene encoding this enzyme in T. gondii. Northern blot analysis shows that two IMPDH transcripts are present in T. gondii tachyzoites. The larger transcript contains an open reading frame of 1,656 nucleotides whose deduced protein sequence consists of 551 amino acids (TgIMPDH). The shorter transcript is an alternative splice product that generates a 371-amino-acid protein lacking the active-site flap (TgIMPDH-S). When TgIMPDH is expressed as a recombinant protein fused to a FLAG tag, the fusion protein localizes to the parasite cytoplasm. Immunoprecipitation with anti-FLAG was employed to purify recombinant TgIMPDH, which converts IMP to XMP as expected. Mycophenolic acid is an uncompetitive inhibitor relative to NAD+, with a intercept inhibition constant (Kii) of 0.03 ± 0.004 μM. Tiazofurin and its seleno analog were not inhibitory to the purified enzyme, but adenine dinucleotide analogs such as TAD and the nonhydrolyzable β-methylene derivatives of TAD or SAD were inhibitory, with Kii values 13- to 60-fold higher than that of mycophenolic acid.

Original languageEnglish
Pages (from-to)2172-2179
Number of pages8
JournalAntimicrobial Agents and Chemotherapy
Volume49
Issue number6
DOIs
StatePublished - Jun 2005

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IMP Dehydrogenase
Toxoplasma
Parasites
Mycophenolic Acid
Inosine Monophosphate
Enzymes
tiazofurin
Pharmacology
Amino Acids
Purines
Proteins
Adenine
Folic Acid
Immunoprecipitation
Recombinant Proteins
Northern Blotting
NAD
Open Reading Frames
Catalytic Domain
Cytoplasm

ASJC Scopus subject areas

  • Pharmacology (medical)

Cite this

IMP dehydrogenase from the protozoan parasite Toxoplasma gondii. / Sullivan, William; Dixon, Stacy E.; Li, Catherine; Striepen, Boris; Queener, Sherry.

In: Antimicrobial Agents and Chemotherapy, Vol. 49, No. 6, 06.2005, p. 2172-2179.

Research output: Contribution to journalArticle

Sullivan, William ; Dixon, Stacy E. ; Li, Catherine ; Striepen, Boris ; Queener, Sherry. / IMP dehydrogenase from the protozoan parasite Toxoplasma gondii. In: Antimicrobial Agents and Chemotherapy. 2005 ; Vol. 49, No. 6. pp. 2172-2179.
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