Department of Chemical Biology, Faculty of Biotechnology, University of Wrocław, Joliot-Curie 14a, 50-383 Wrocław, Poland.
Inorg Chem. 2021 Apr 5;60(7):4657-4675. doi: 10.1021/acs.inorgchem.0c03639. Epub 2021 Mar 18.
Phytochelatins (PCs) are short Cys-rich peptides with repeating γ-Glu-Cys motifs found in plants, algae, certain fungi, and worms. Their biosynthesis has been found to be induced by heavy metals-both biogenic and toxic. Among all metal inducers, Cd(II) has been the most explored from a biological and chemical point of view. Although Cd(II)-induced PC biosynthesis has been widely examined, still little is known about the structure of Cd(II) complexes and their thermodynamic stability. Here, we systematically investigated glutathione (GSH) and PC2-PC6 systems, with regard to their complex stoichiometries and spectroscopic and thermodynamic properties. We paid special attention to the determination of stability constants using several complementary techniques. All peptides form CdL complexes, but CdL was found for GSH, PC2, and partially for PC3. Moreover, binuclear species CdL were identified for the series PC3-PC6 in an excess of Cd(II). Potentiometric and competition spectroscopic studies showed that the affinity of Cd(II) complexes increases from GSH to PC4 almost linearly from micromolar (log = 5.93) to the femtomolar range (log = 13.39) and additional chain elongation does not increase the stability significantly. Data show that PCs form an efficient system which buffers free Cd(II) ions in the pico- to femtomolar range under cellular conditions, avoiding significant interference with Zn(II) complexes. Our study confirms that the favorable entropy change is the factor governing the elevation of phytochelatins' stability and illuminates the importance of the chelate effect in shifting the free Gibbs energy.
植物螯合肽（PCs）是一类富含半胱氨酸的短肽，在植物、藻类、某些真菌和蠕虫中发现，具有重复的 γ-Glu-Cys 基序。它们的生物合成已被发现可被重金属诱导，包括生物来源的和有毒的重金属。在所有金属诱导剂中，Cd(II)从生物学和化学角度来看是研究最多的。尽管 Cd(II)诱导的 PC 生物合成已被广泛研究，但对 Cd(II)配合物的结构及其热力学稳定性仍知之甚少。在这里，我们系统地研究了谷胱甘肽（GSH）和 PC2-PC6 体系，涉及它们的配合物化学计量比、光谱和热力学性质。我们特别关注使用几种互补技术确定稳定常数。所有肽都形成 CdL 配合物，但 GSH、PC2 和部分 PC3 形成 CdL。此外，在 Cd(II)过量的情况下，我们还鉴定了 PC3-PC6 系列的双核物种 CdL。电位和竞争光谱研究表明，Cd(II)配合物的亲和力从 GSH 到 PC4 几乎呈线性增加，从微摩尔（log = 5.93）到飞摩尔范围（log = 13.39），并且链的进一步延长不会显著增加稳定性。数据表明，PCs 形成了一个有效的体系，可以在细胞条件下缓冲皮摩尔到飞摩尔范围内的游离 Cd(II)离子，避免与 Zn(II)配合物发生显著干扰。我们的研究证实了有利的熵变是提高植物螯合肽稳定性的因素，并阐明了螯合效应在改变自由吉布斯能方面的重要性。
