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Inhibition and Structure of Toxoplasma gondii Purine Nucleoside Phosphorylase.

(2014) Eukaryot Cell 13: 572-579

• PubMed: 24585883 Search on PubMedSearch on PubMed Central
• DOI: https://doi.org/10.1128/EC.00308-13
• Primary Citation of Related Structures:  
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• PubMed Abstract: 
  

  The intracellular pathogen Toxoplasma gondii is a purine auxotroph that relies on purine salvage for proliferation. We have optimized T. gondii purine nucleoside phosphorylase (TgPNP) stability and crystallized TgPNP with phosphate and immucillin-H, a transition-state analogue that has high affinity for the enzyme. Immucillin-H bound to TgPNP with a dissociation constant of 370 pM, the highest affinity of 11 immucillins selected to probe the catalytic site. The specificity for transition-state analogues indicated an early dissociative transition state for TgPNP. Compared to Plasmodium falciparum PNP, large substituents surrounding the 5'-hydroxyl group of inhibitors demonstrate reduced capacity for TgPNP inhibition. Catalytic discrimination against large 5' groups is consistent with the inability of TgPNP to catalyze the phosphorolysis of 5'-methylthioinosine to hypoxanthine. In contrast to mammalian PNP, the 2'-hydroxyl group is crucial for inhibitor binding in the catalytic site of TgPNP. This first crystal structure of TgPNP describes the basis for discrimination against 5'-methylthioinosine and similarly 5'-hydroxy-substituted immucillins; structural differences reflect the unique adaptations of purine salvage pathways of Apicomplexa.

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Organizational Affiliation: 

Department of Microbiology and Immunology, Albert Einstein College of Medicine, Yeshiva University, Bronx, New York, USA.