Identification and characterisation of high affinity nucleoside and nucleobase transporters in Toxoplasma gondii
Identification and characterisation of high affinity nucleoside and nucleobase transporters in Toxoplasma gondii
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DOI：
10.1016/s0020-7519(03)00091-2
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发表时间：
2003-07-30
影响因子：
4
通讯作者：
Wastling, JM
中科院分区：
文献类型：
--
作者：
De Koning, HP;Al-Salabi, MI;Wastling, JM
原生动物寄生虫刚地弓形虫依赖于抢救它所需要的嘌呤。我们重新分析了弓形虫的嘌呤转运，并鉴定了新的核苷和核碱基转运体。后者转运次黄嘌呤（TgNBT1; K-m = 0.91 +/- 0.19 muM），受到鸟嘌呤和黄嘌呤的抑制，是在顶复合体寄生虫中发现的第一个高亲和力核碱基转运蛋白。先前报道的核苷转运体TgAT1对腺苷和莫西分别具有低亲和力，K-m值分别为105和134 muM。我们现在已经确定了第二种核苷转运蛋白TgAT2，它具有高亲和力，可被腺苷、莫西、鸟苷、尿苷和胸苷（K-m值0.28 +/- 1.5 muM）以及胞苷（K-i = 32 muM）抑制。TgAT2还识别出几种具有治疗潜力的核苷类似物。我们研究了TgAT2广泛特异性的基础，发现它与3‘和5’羟基形成氢键，碱基与嘌呤环的N3或嘧啶环的N(3)H通过氢键结合，并且很可能是pi-pi堆叠。这些高亲和力嘌呤核碱基和核苷转运体的鉴定首次将胞内环境中游离核苷和核碱基的低丰度与弓形虫进行的高效嘌呤回收相协调。(C) 2003澳大利亚寄生虫学学会Elsevier Science Ltd.出版。版权所有。
The protozoan parasite Toxoplasma gondii depends upon salvaging the purines that it requires. We have re-analysed purine transport in T gondii and identified novel nucleoside and nucleobase transporters. The latter transports hypoxanthine (TgNBT1; K-m = 0.91 +/- 0.19 muM) and is inhibited by guanine and xanthine: it is the first high affinity nucleobase transporter to be identified in an apicomplexan parasite. The previously reported nucleoside transporter, TgAT1, is low affinity with K-m values of 105 and 134 muM for adenosine and mosine, respectively. We have now identified a second nucleoside transporter, TgAT2, which is high affinity and inhibited by adenosine, mosine, guanosine, uridine and thymidine (K-m values 0.28 +/- 1.5 muM) as well as cytidine (K-i = 32 muM). TgAT2 also recognises several nucleoside analogues with therapeutic potential. We have investigated the basis for the broad specificity of TgAT2 and found that hydrogen bonds are formed with the 3' and 5' hydroxyl groups and that the base groups are bound through H-bonds with either N3 of the purine ring or N(3)H of the pyrimidine ring, and most probably pi-pi-stacking as well. The identification of these high affinity purine nucleobase and nucleoside transporters reconciles for the first time the low abundance of free nucleosides and nucleobases in the intracellular environment with the efficient purine salvage carried out by T gondii. (C) 2003 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.