title: 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.affiliation: Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
authors.forename: Meng-Chiao
authors.initials: MC
authors.lastname: Ho
authors.forename: Wuxian
authors.initials: W
authors.lastname: Shi
authors.forename: Agnes
authors.initials: A
authors.lastname: Rinaldo-Matthis
authors.forename: Peter C
authors.initials: PC
authors.lastname: Tyler
authors.forename: Gary B
authors.initials: GB
authors.lastname: Evans
authors.forename: Keith
authors.initials: K
authors.lastname: Clinch
authors.forename: Steven C
authors.initials: SC
authors.lastname: Almo
authors.forename: Vern L
authors.initials: VL
authors.lastname: Schramm
mesh_terms: D000818:Animals; D020134:Catalytic Domain; D002417:Cattle; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000494:pharmacology; D006801:Humans; D008958:Models, Molecular; D011487:Protein Conformation; D011684:Purine Nucleosides / Q000737:chemistry / Q000494:pharmacology; D011683:Purine-Nucleoside Phosphorylase / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D011744:Pyrimidinones / Q000737:chemistry / Q000494:pharmacology; D011759:Pyrrolidines / Q000737:chemistry / Q000494:pharmacology; D013816:Thermodynamics
chemical_list: C508755:DADMe-immucillin H; D004791:Enzyme Inhibitors; D011684:Purine Nucleosides; D011744:Pyrimidinones; D011759:Pyrrolidines; C113101:forodesine; D011683:Purine-Nucleoside Phosphorylase