title: Novel Characteristics of Trypanosoma brucei Guanosine 5'-monophosphate Reductase Distinct from Host Animals.
abstract: The metabolic pathway of purine nucleotides in parasitic protozoa is a potent drug target for treatment of parasitemia. Guanosine 5'-monophosphate reductase (GMPR), which catalyzes the deamination of guanosine 5'-monophosphate (GMP) to inosine 5'-monophosphate (IMP), plays an important role in the interconversion of purine nucleotides to maintain the intracellular balance of their concentration. However, only a few studies on protozoan GMPR have been reported at present. Herein, we identified the GMPR in Trypanosoma brucei, a causative protozoan parasite of African trypanosomiasis, and found that the GMPR proteins were consistently localized to glycosomes in T. brucei bloodstream forms. We characterized its recombinant protein to investigate the enzymatic differences between GMPRs of T. brucei and its host animals. T. brucei GMPR was distinct in having an insertion of a tandem repeat of the cystathionine β-synthase (CBS) domain, which was absent in mammalian and bacterial GMPRs. The recombinant protein of T. brucei GMPR catalyzed the conversion of GMP to IMP in the presence of NADPH, and showed apparent affinities for both GMP and NADPH different from those of its mammalian counterparts. Interestingly, the addition of monovalent cations such as K+ and NH4+ to the enzymatic reaction increased the GMPR activity of T. brucei, whereas none of the mammalian GMPR's was affected by these cations. The monophosphate form of the purine nucleoside analog ribavirin inhibited T. brucei GMPR activity, though mammalian GMPRs showed no or only a little inhibition by it. These results suggest that the mechanism of the GMPR reaction in T. brucei is distinct from that in the host organisms. Finally, we demonstrated the inhibitory effect of ribavirin on the proliferation of trypanosomes in a dose-dependent manner, suggesting the availability of ribavirin to develop a new therapeutic agent against African trypanosomiasis.
authors.affiliation: Laboratory of Biological Macromolecules, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka, Japan.
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Bessho
authors.affiliation: Laboratory of Biological Macromolecules, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Okada
authors.affiliation: Laboratory of Biological Macromolecules, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka, Japan.
authors.forename: Chihiro
authors.initials: C
authors.lastname: Kimura
authors.affiliation: Laboratory of Biological Macromolecules, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Shinohara
authors.affiliation: Laboratory of Biological Macromolecules, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka, Japan.
authors.forename: Ai
authors.initials: A
authors.lastname: Tomiyama
authors.affiliation: Laboratory of Biological Macromolecules, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Imamura
authors.affiliation: Laboratory of Veterinary Pathology, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Izumisano, Osaka, Japan.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Kuwamura
authors.affiliation: Laboratory of Toxicology, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Izumisano, Osaka, Japan.
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Nishimura
authors.affiliation: Laboratory of Biodefense and Regulation, Osaka University of Pharmaceutical Sciences, Takatsuki, Osaka, Japan.
authors.forename: Ko
authors.initials: K
authors.lastname: Fujimori
authors.affiliation: Laboratory of Organic Chemistry for Drug Development, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Shuto
authors.affiliation: Laboratory of Biological Macromolecules, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Ishibashi
authors.affiliation: AU/NEPAD Agency Regional Office for Eastern and Central Africa, Nairobi, Kenya.
authors.forename: Bruno Kilunga
authors.initials: BK
authors.lastname: Kubata
authors.affiliation: Laboratory of Biological Macromolecules, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Inui
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D050899:GMP Reductase / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D011994:Recombinant Proteins; D012254:Ribavirin / Q000494:pharmacology; D013045:Species Specificity; D013696:Temperature; D014344:Trypanocidal Agents / Q000494:pharmacology; D014346:Trypanosoma brucei brucei / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
chemical_list: D000963:Antimetabolites; D011994:Recombinant Proteins; D014344:Trypanocidal Agents; D012254:Ribavirin; D050899:GMP Reductase