Four generations of transition-state analogues for human purine nucleoside phosphorylase

Meng Chiao Ho, Wuxian Shi, Agnes Rinaldo-Matthis, Peter C. Tyler, Gary B. Evans, Keith Clinch, Steven C. Almo, Vern L. Schramm

Research output: Contribution to journalArticlepeer-review

68 Scopus citations


Inhibition of human purine nucleoside phosphorylase (PNP) stops growth of activated T-cells and the formation of 6-oxypurine bases, making it a target for leukemia, autoimmune disorders, and gout. Four generations of ribocation transition-state mimics bound to PNP are structurally characterized. Immucillin-H (K*i = 58 pM, firstgeneration) contains an iminoribitol cation with four asymmetric carbons. DADMe-Immucillin-H (K*i = 9 pM, second-generation), uses a methylene-bridged dihydroxypyrrolidine cation with two asymmetric centers.DATMe-Immucillin-H (K*i = 9 pM, third-generation) contains an open-chain amino alcohol cation with two asymmetric carbons. SerMe-ImmH (K*i = 5 pM, fourth-generation) uses achiral dihydroxyaminoalcohol seramide as the ribocation mimic. Crystal structures of PNPs establish features of tight binding to be; 1) ion-pair formation between bound phosphate (or its mimic) and inhibitor cation, 2) leaving-group interactions to N1, O6, and N7 of 9-deazahypoxanthine, 3) interaction between phosphate and inhibitor hydroxyl groups, and 4) His257 interacting with the 5′-hydroxyl group. The first generation analogue is an imperfect fit to the catalytic site with a long ion pair distance between the iminoribitol and bound phosphate and weaker interactions to the leaving group. Increasing the ribocation to leaving-group distance in the second- to fourth-generation analogues provides powerful binding interactions and a facile synthetic route to powerful inhibitors. Despite chemical diversity in the four generations of transitionstate analogues, the catalytic site geometry is almost the same for all analogues. Multiple solutions in transition-state analogue design are available to convert the energy of catalytic rate enhancement to binding energy in human PNP.

Original languageEnglish (US)
Pages (from-to)4805-4812
Number of pages8
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number11
StatePublished - Mar 16 2010


  • Enzyme structure
  • Immucillins
  • Inhibitor design
  • T-cells disorders
  • Tight-binding

ASJC Scopus subject areas

  • General


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