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

Abstract

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(1/4) 58 pM, first generation)contains an iminoribitol cation with four asymmetric carbons. DADMe-Immucillin-H (K*i(1/4) 9 pM, second-generation),uses a methylene-bridged dihydroxypyrrolidine cation with twoasymmetric centers.DATMe-Immucillin-H (K*i(1/4)9 pM, third-generation) contains an open-chain amino alcohol cation with two asymmetric carbons. SerMe-ImmH (K*i(1/4) 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 transition-state 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.

• Authors: Meng-Chiao Ho, Wuxian Shi, Agnes Rinaldo-Matthis, Peter C Tyler, Gary B Evans, Keith Clinch, Steven C Almo, Vern L Schramm
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 107 Issue 11 Pg. 4805-12 (Mar 16 2010) ISSN: 1091-6490 [Electronic] United States
• PMID: 20212140 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• DADMe-immucillin H
• Enzyme Inhibitors
• Purine Nucleosides
• Pyrimidinones
• Pyrrolidines
• forodesine
• Purine-Nucleoside Phosphorylase

Topics

• Animals
• Catalytic Domain
• Cattle
• Enzyme Inhibitors (chemistry, pharmacology)
• Humans
• Models, Molecular
• Protein Conformation
• Purine Nucleosides (chemistry, pharmacology)
• Purine-Nucleoside Phosphorylase (antagonists & inhibitors, chemistry)
• Pyrimidinones (chemistry, pharmacology)
• Pyrrolidines (chemistry, pharmacology)
• Thermodynamics