Plasmodium falciparum purine nucleoside phosphorylase: Crystal structures, immucillin inhibitors, and dual catalytic function

Wuxian Shi, Li Min Ting, Gregory A. Kicska, Andrzej Lewandowicz, Peter C. Tyler, Gary B. Evans, Richard H. Furneaux, Kami Kim, Steve C. Almo, Vern L. Schramm

Research output: Contribution to journalArticle

106 Scopus citations

Abstract

Purine nucleoside phosphorylase from Plasmodium falciparum (PfPNP) is an anti-malarial target based on the activity of Immucillins. The crystal structure of PfPNP·Immucillin-H (ImmH)·SO4 reveals a homohexamer with ImmH and SO4 bound at each catalytic site. A solvent-filled cavity close to the 5′-hydroxyl group of ImmH suggested that PfPNP can accept additional functional groups at the 5′-carbon. Assays established 5′-methyl-thioinosine (MTI) as a substrate for PfPNP. MTI is not found in human metabolism. These properties of PfPNP suggest unusual purine pathways in P. falciparum and provide structural and mechanistic foundations for the design of malaria-specific transition state analogue inhibitors. 5′-Methylthio-Immucillin-H (MT-ImmH) was designed to resemble the transition state of PfPNP and binds to PfPNP and human-PNP with K d values of 2.7 and 303 nM, respectively, to give a discrimination factor of 112. MT-ImmH is the first inhibitor that favors PfPNP inhibition. The structure of PfPNP·MT-ImmH.SO4 shows that the hydrophobic methylthio group inserts into a hydrophobic region adjacent to the more hydrophilic 5′-hydroxyl binding site of ImmH. The catalytic features of PfPNP indicate a dual cellular function in purine salvage and polyamine metabolism. Combined metabolic functions in a single enzyme strengthen the rationale for targeting PfPNP in anti-malarial action.

Original languageEnglish (US)
Pages (from-to)18103-18106
Number of pages4
JournalJournal of Biological Chemistry
Volume279
Issue number18
DOIs
StatePublished - Apr 30 2004

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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