Metallothioneins (MTs) are a large superfamily of ubiquitous cysteine-rich metalloproteins with main functions in metal ion homeostasis and detoxification. Neclu_MT1 is a metallothionein from the aquatic fungus Heliscus lugdunensis and so far the only known MT that is solely induced by Cd^II but not by Zn^II or copper ions. In addition to eight cysteine residues, Neclu_MT1 also contains a less common single C-terminal histidine residue. To better understand the role of this histidine residue in metal ion binding, for the first time, potentiometric pH titrations are applied, revealing insights into the protonation and metal ion binding processes. Additional studies with absorption and NMR spectroscopy complement the finding that while the histidine residue is not crucial for the overall metal binding capacity, it does serve as a ligand in the Zn^II but not in the Cd^II form of the protein.

中文翻译：

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在水生真菌特定于镉的金属硫蛋白中，组氨酸残基对镉和锌的不同行为

金属硫蛋白（MTs）是一个普遍存在的富含半胱氨酸的金属蛋白的大家族，在金属离子的稳态和排毒中起主要作用。Neclu_MT1是一种来自水生真菌Heliscus lugdunensis的金属硫蛋白，也是迄今为止唯一已知的仅由Cd ^II诱导而不由Zn ^II诱导的MT。或铜离子。除八个半胱氨酸残基外，Neclu_MT1还包含较少见的单个C端组氨酸残基。为了更好地了解该组氨酸残基在金属离子结合中的作用，首次采用电位pH滴定法，揭示了对质子化和金属离子结合过程的见解。利用吸收光谱和NMR光谱进行的其他研究补充了以下发现：组氨酸残基对整体金属结合能力并不重要，但它确实可以作为Zn ^II的配体而不是以Cd ^II的形式存在。