Parasitology



Identification of the first pyrimidine nucleobase transporter in Leishmania: similarities with the Trypanosoma brucei U1 transporter and antileishmanial activity of uracil analogues


I. G. PAPAGEORGIOU a1a3, L. YAKOB a2, M. I. AL SALABI a2, G. DIALLINAS a3, K. P. SOTERIADOU a1 and H. P. DE KONING a2c1
a1 Department of Biochemistry, Hellenic Pasteur Institute, 127 Vassilissis Sophias, 115 21 Athens, Greece
a2 Institute of Biomedical and Life Sciences, Division of Infection and Immunity, University of Glasgow, Glasgow G12 8QQ, UK
a3 Department of Botany, Faculty of Biology, University of Athens, Panepistimioupolis 15781 Athens, Greece

Article author query
papageorgiou ig   [PubMed][Google Scholar] 
yakob l   [PubMed][Google Scholar] 
al salabi mi   [PubMed][Google Scholar] 
diallinas g   [PubMed][Google Scholar] 
soteriadou kp   [PubMed][Google Scholar] 
de koning hp   [PubMed][Google Scholar] 

Abstract

While purine transport has been widely studied in protozoa, almost nothing is known about their capacity to salvage pyrimidines. Here, we report a Leishmania major transporter with high affinity for uracil (Km=0·32±0·07 μM) which we designated LmU1. This transporter displayed a high degree of specificity, as it had virtually no affinity for cytosine, thymine or purine nucleobases, nor did it transport pyrimidine nucleosides. Highest affinity was for 5-fluorouracil. The results show that the permeant binding site of LmU1 interacts strongly with the keto groups of uracil, as shown by a low affinity for 2-thio- and 4-thiouracil. LmU1 appears to further bind uracil through a weak hydrogen bond with N(1)H of the pyrimidine ring in addition to a stronger H-bond with N(3)H. Substrate binding and selectivity were strikingly similar to that of the U1 transporter in the related kinetoplastid Trypanosoma brucei. Uracil analogues likely to be transported by LmU1 were also screened for antileishmanial activity, with 5-fluorouracil displaying strong activity against promastigotes and intracellular amastigotes. Overall, the results show that, like purine nucleobase transport, pyrimidine nucleobase transport function is very similar in L. major and T. brucei insect forms.

(Received March 4 2004)
(Revised August 16 2004)
(Accepted August 17 2004)


Key Words: Leishmania major; Trypanosoma brucei; pyrimidine transporters; purine transporters; uracil transporter; 5-fluorouracil.

Correspondence:
c1 Institute of Biomedical and Life Sciences, Division of Infection and Immunity, University of Glasgow, Glasgow G12 8QQ, UK. Tel/Fax: +44 141 3303753. E-mail: h.de-koning@bio.gla.ac.uk


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