Trypanosomal nucleoside hydrolase. A novel mechanism from the structure with a transition-state inhibitor. Academic Article uri icon


  • Nucleoside N-ribohydrolases are targets for disruption of purine salvage in the protozoan parasites. The structure of a trypanosomal N-ribohydrolase in complex with a transition-state inhibitor is reported at 2.3 A resolution. The nonspecific nucleoside hydrolase from Crithidia fasciculata cocrystallized with p-aminophenyliminoribitol reveals tightly bound Ca2+ as a catalytic site ligand. The complex with the transition-state inhibitor is characterized by (1) large protein conformational changes to create a hydrophobic leaving group site (2) C3'-exo geometry for the inhibitor, typical of a ribooxocarbenium ion (3) stabilization of the ribooxocarbenium analogue between the neighboring group 5'-hydroxyl and bidentate hydrogen bonds to Asn168; and (4) octacoordinate Ca2+ orients a catalytic site water and is liganded to two hydroxyls of the inhibitor. The mechanism is ribooxocarbenium stabilization with weak leaving group activation and is a departure from glucohydrolases which use paired carboxylates to achieve the transition state.

published proceedings

  • Biochemistry

author list (cited authors)

  • Degano, M., Almo, S. C., Sacchettini, J. C., & Schramm, V. L.

citation count

  • 82

complete list of authors

  • Degano, M||Almo, SC||Sacchettini, JC||Schramm, VL

publication date

  • May 1998