The four members of the Drosophila metallothionein family exhibit distinct yet overlapping roles in heavy metal homeostasis and detoxification
The four members of the Drosophila metallothionein family exhibit distinct yet overlapping roles in heavy metal homeostasis and detoxification
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DOI：
10.1111/j.1365-2443.2006.00971.x
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发表时间：
2006-06-01
期刊：
影响因子：
2.1
通讯作者：
Atrian, Silvia
中科院分区：
文献类型：
--
作者：
Egli, Dieter;Domenach, Jordi;Atrian, Silvia
果蝇基因组中存在四种金属硫蛋白基因，分别命名为 MtnA、MtnB、MtnC、MtnD，所有这些基因均通过相同的金属响应转录因子 MTF-1 由重金属诱导转录。在这里，我们通过定向诱变表明，四种金属硫蛋白基因在重金属稳态和毒性预防中表现出不同但重叠的作用。在各个金属硫蛋白突变体中，它们之间最显着的区别是 MtnA 缺陷型果蝇对铜负荷最敏感，而 MtnB 缺陷型果蝇对镉最敏感。使用各种报告基因构建体和 mRNA 定量，我们表明 MtnA 启动子优先由铜诱导，而 MtnB 启动子优先由镉诱导。这种金属偏好也在蛋白质水平上观察到，因为铜和镉与 MtnA 和 MtnB 的络合物的化学计量、光谱测定和光谱特征与铜-MtnA 和镉-MtnB 的更高稳定性密切相关。最后，MtnC 和 MtnD 都与 MtnB 非常相似，与 MtnA 或 MtnB 相比，它们表现出较低的铜和镉结合能力。根据这些结合研究，MtnC 或 MtnD 的果蝇突变体具有接近野生型水平的对铜或镉负载的抵抗力。此外，MtnA 和 MtnB 的眼特异性过度表达，而非 MtnC 或 MtnD 的过度表达，可以挽救由眼内铜负荷引起的“粗糙眼”表型。总而言之，虽然 MtnC 和 MtnD 的确切作用仍有待确定，但 MtnA 和 MtnB 分别对铜和镉毒性的优先保护是启动子偏好和金属结合相结合的结果。
Four metallothionein genes are present in the Drosophila melanogaster genome, designated MtnA, MtnB, MtnC, MtnD, all of which are transcriptionally induced by heavy metals through the same metal-responsive transcription factor, MTF-1. Here we show, by targeted mutagenesis, that the four metallothionein genes exhibit distinct, yet overlapping, roles in heavy metal homeostasis and toxicity prevention. Among the individual metallothionein mutants, the most prominent distinction between them was that MtnA-defective flies were the most sensitive to copper load, while MtnB-defective flies were the most sensitive to cadmium. Using various reporter gene constructs and mRNA quantification, we show that the MtnA promoter is preferentially induced by copper, while the MtnB promoter is preferentially induced by cadmium. Such a metal preference is also observed at the protein level as the stoichiometric, spectrometric and spectroscopic features of the copper and cadmium complexes with MtnA and MtnB correlate well with a greater stability of copper-MtnA and cadmium-MtnB. Finally, MtnC and MtnD, both of which are very similar to MtnB, display lower copper and cadmium binding capabilities compared to either MtnA or MtnB. In accordance with these binding studies, Drosophila mutants of MtnC or MtnD have a near wild type level of resistance against copper or cadmium load. Furthermore, eye-specific over-expression of MtnA and MtnB, but not of MtnC or MtnD, can rescue a "rough eye" phenotype caused by copper load in the eye. Taken together, while the exact roles of MtnC and MtnD remain to be determined, the preferential protection against copper and cadmium toxicity by MtnA and MtnB, respectively, are the result of a combination of promoter preference and metal binding.