Selective metal binding by Vanabin2 from the vanadium-rich ascidian, Ascidia sydneiensis samea.
Selective metal binding by Vanabin2 from the vanadium-rich ascidian, Ascidia sydneiensis samea.
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DOI：
10.1016/j.bbagen.2006.03.013
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发表时间：
2006-07
期刊：
影响因子：
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通讯作者：
Norifumi Kawakami;T. Ueki;K. Matsuo;K. Gekko;H. Michibata
中科院分区：
文献类型：
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作者：
Norifumi Kawakami;T. Ueki;K. Matsuo;K. Gekko;H. Michibata
钒结合蛋白（Vanabins）是从富含钒的海鞘（Ascidia sydneiensis samea）中分离出来的。最近的报道表明，Vanabin 2在pH 7.5下结合20个V（IV）离子，并且它具有新颖的弓形构象。然而，Vanabin 2在海鞘积累钒中的作用尚未确定。在本研究中，酸性pH值的选择性金属结合的Vanabin 2和Vanabin 2的二级结构的影响进行了检查。在酸性条件下，Vanabin 2选择性地与V（IV）、Fe（III）和Cu（II）离子结合。相比之下，Co（II）、Ni（II）和Zn（II）离子在pH 6.5下结合，但在pH 4.5下不结合。在酸性条件下，pH值的变化对Vanabin 2的二级结构没有可检测的影响，如通过圆二色性光谱测定的，并且在pH 4.5-7.5的范围内观察到V（IV）离子的解离常数的变化很小，这表明配体的结合状态不受酸化的影响。两者合计，这些结果表明，酸化后金属离子解离的原因是不可归因于二级结构的变化，而是由与V（IV）离子络合的氨基酸配体的质子化引起的。
Vanadium-binding proteins, or Vanabins, have recently been isolated from the vanadium-rich ascidian, Ascidia sydneiensis samea. Recent reports indicate that Vanabin2 binds twenty V(IV) ions at pH 7.5, and that it has a novel bow-shaped conformation. However, the role of Vanabin2 in vanadium accumulation by the ascidian has not yet been determined. In the present study, the effects of acidic pH on selective metal binding to Vanabin2 and on the secondary structure of Vanabin2 were examined. Vanabin2 selectively bound to V(IV), Fe(III), and Cu(II) ions under acidic conditions. In contrast, Co(II), Ni(II), and Zn(II) ions were bound at pH 6.5 but not at pH 4.5. Changes in pH had no detectable effect on the secondary structure of Vanabin2 under acidic conditions, as determined by circular dichroism spectroscopy, and little variation in the dissociation constant for V(IV) ions was observed in the pH range 4.5–7.5, suggesting that the binding state of the ligands is not affected by acidification. Taken together, these results suggest that the reason for metal ion dissociation upon acidification is attributable not to a change in secondary structure but, rather, that it is caused by protonation of the amino acid ligands that complex with V(IV) ions.