title: Trypanosoma brucei Methylthioadenosine Phosphorylase Protects the Parasite from the Antitrypanosomal Effect of Deoxyadenosine: IMPLICATIONS FOR THE PHARMACOLOGY OF ADENOSINE ANTIMETABOLITES.
abstract: Trypanosoma brucei causes African sleeping sickness for which no vaccine exists and available treatments are of limited use due to their high toxicity or lack of efficacy. T. brucei cultivated in the presence of deoxyadenosine accumulates high levels of dATP in an adenosine kinase-dependent process and dies within a few hours. Here we show that T. brucei treated with 1 mm deoxyadenosine accumulates higher dATP levels than mammalian cells but that this effect diminishes quickly as the concentration of the deoxynucleoside decreases. Radioactive tracer studies showed that the parasites are partially protected against lower concentrations of deoxyadenosine by the ability to cleave it and use the adenine for ATP synthesis. T. brucei methylthioadenosine phosphorylase (TbMTAP) was found to be responsible for the cleavage as indicated by the phosphate dependence of deoxyadenosine cleavage in T. brucei cell extracts and increased deoxyadenosine sensitivity in TbMTAP knockdown cells. Recombinant TbMTAP exhibited higher turnover number (kcat) and Km values for deoxyadenosine than for the regular substrate, methylthioadenosine. One of the reaction products, adenine, inhibited the enzyme, which might explain why TbMTAP-mediated protection is less efficient at higher deoxyadenosine concentrations. Consequently, T. brucei grown in the presence of adenine demonstrated increased sensitivity to deoxyadenosine. For deoxyadenosine/adenosine analogues to remain intact and be active against the parasite, they need to either be resistant to TbMTAP-mediated cleavage, which is the case with the three known antitrypanosomal agents adenine arabinoside, tubercidin, and cordycepin, or they need to be combined with TbMTAP inhibitors.
authors.affiliation: From the Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87 Umeå, Sweden and.
authors.forename: Munender
authors.initials: M
authors.lastname: Vodnala
authors.affiliation: From the Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87 Umeå, Sweden and.
authors.forename: Farahnaz
authors.initials: F
authors.lastname: Ranjbarian
authors.affiliation: From the Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87 Umeå, Sweden and.
authors.forename: Anna
authors.initials: A
authors.lastname: Pavlova
authors.affiliation: Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8TA, Scotland, United Kingdom.
authors.forename: Harry P
authors.initials: HP
authors.lastname: de Koning
authors.affiliation: From the Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87 Umeå, Sweden and anders.hofer@umu.se.
authors.forename: Anders
authors.initials: A
authors.lastname: Hofer
mesh_terms: D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology*; D041702:BALB 3T3 Cells; D015153:Blotting, Western; D003839:Deoxyadenosines / Q000494:pharmacology*; D004285:Dogs; D018922:HL-60 Cells; D006801:Humans; D061985:Madin Darby Canine Kidney Cells; D051379:Mice; D011683:Purine-Nucleoside Phosphorylase / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000187:drug effects* / Q000201:enzymology* / Q000472:pathogenicity; D014353:Trypanosomiasis, African / Q000469:parasitology / Q000473:pathology* / Q000517:prevention & control
chemical_list: D000963:Antimetabolites; D003839:Deoxyadenosines; D011683:Purine-Nucleoside Phosphorylase; C021784:5'-methylthioadenosine phosphorylase; C058118:2'-deoxyadenosine
keywords: Trypanosoma brucei; methylthioadenosine phosphorylase (MTAP); nucleoside/nucleotide analogue; nucleoside/nucleotide metabolism; parasite; trypanosome