Polythiol binding of metal ions plays crucial role in the proper functioning of cysteine-rich proteins that are responsible for metal homeostasis and defending processes against metal toxicity (including heavy metals detoxification). The coordination properties of cysteine residues involved in specific sequencional patterns in proteins (like those present in e.g. metallothioneins) are interesting not only from a chemical point of view but may also lead to a better understanding of the purpose and allocation of metal ions in various biomolecules. In this study, the interaction of Zn2+, Cd2+ and Ni2+ ions with four peptides containing cysteine triplet motif were studied by potentiometric and spectroscopic methods. The main goal of this research was to answer the question how effectively three thiols, each being next to other, are able to bind single metal ion. Two of peptides contain additional, fourth cysteine residue, separated from triplet by two and three other amino acid residues. As results show, all three cysteine residues in the CCC motif are able to participate in the coordination of the metal ion (Cd2+, Zn2+). Except cysteine thiol groups, amide nitrogen atoms are also involved in the coordination of Ni2+.

中文翻译：

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半胱氨酸三联体-协调谜团？

金属离子的多硫醇结合在富含半胱氨酸的蛋白质的正常功能中起着至关重要的作用，这些蛋白质负责金属的稳态和防御金属毒性（包括重金属解毒）的过程。蛋白质中特定顺序模式中涉及的半胱氨酸残基的配位特性（例如金属硫蛋白中存在的半胱氨酸残基）不仅从化学角度来看很有趣，而且还可能导致人们更好地理解金属离子在各种生物分子中的用途和分配。在这项研究中，Zn2 +，Cd2 +和Ni2 +离子与四个含有半胱氨酸三联体基序的肽的相互作用通过电位和光谱法进行了研究。这项研究的主要目的是回答以下问题：三个硫醇彼此相邻的效率如何，能够结合单个金属离子。两种肽含有另外的第四个半胱氨酸残基，其与三联体之间被两个和三个其他氨基酸残基隔开。结果表明，CCC基序中的所有三个半胱氨酸残基均能够参与金属离子（Cd2 +，Zn2 +）的配位。除半胱氨酸硫醇基团外，酰胺氮原子还参与Ni2 +的配位。