Linear free-energy analysis of mercury(II) and cadmium(II) binding to three-stranded coiled coils
Linear free-energy analysis of mercury(II) and cadmium(II) binding to three-stranded coiled coils
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DOI：
10.1021/bi0506674
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发表时间：
2005-08-09
期刊：
影响因子：
2.9
通讯作者：
Pecoraro, VL
中科院分区：
文献类型：
--
作者：
Ghosh, D;Lee, KH;Pecoraro, VL
研究人员已经研究了蛋白质如何在金属中心上实施非标准几何形状，以评估蛋白质结构如何定义活性位点金属辅因子的配位几何形状和结合亲和力的问题。我们已经表明，TRI肽系列[AcG-（LKALEEK）（4）G-NH 2]的半胱氨酸取代版本以不同于水溶液中通常发现的巯基配体的几何形状结合Hg-II和Cd-II。一个基本的问题是，这种结构扰动是否是由于蛋白质的影响或金属几何形状偏好的变化。为了解决这个问题，我们已经完成了线性自由能分析，该分析将三链卷曲螺旋在不存在金属的情况下与肽对重金属Hg-II和CO的结合亲和力相关联。在本文中，已经合成了这个家族的六个新成员，用较小且疏水性较低的残基取代核心亮氨酸残基，从而导致不同程度的自缔合亲和力。与此同时，一些更小和更长的测序肽的研究也进行了检查。所有这些肽被认为是螯合汞-II和镉-II在一个不常见的三角环境。对于这两种金属，结合是强的微摩尔解离常数。对于Hg-II与肽的结合，对于第三个硫醇盐与线性Hg-II（pep）2物质的结合，解离常数范围从Baby L12 C的2.4 x 10（-5）M到Grand L9 C的2.5 x 10（-9）M。Hg-II与肽Grand L9 C的结合在金属调节蛋白汞响应（merR）中的金属结合的能量学上是相似的，在纳摩尔金属浓度下显示出类似于50%三角形HgII形成。大约11 kcal/mol的Hg-II（Grand L9 C）（3）（-）稳定性是由于肽相互作用，而只有1-4 kcal/mol的稳定性是由Hg-II（RS）（2）结合第三个硫醇配体产生的。这进一步验证了这样的假设：merR等蛋白质系统中有利的三级相互作用对于稳定生物系统中的非自然协调环境有很大帮助。类似地，对于Cd-II与TRI家族的结合，解离常数范围从Baby L9 C的1.3 x 10（-6）M到TRI L9 C的8.3 x 10（-9）M，显示出稳定聚集体形成的类似性质。
Investigators have studied how proteins enforce nonstandard geometries on metal centers to assess the question of how protein structures can define the coordination geometry and binding affinity of an active-site metal cofactor. We have shown that cysteine-substituted versions of the TRI peptide series [AcG-(LKALEEK)(4)G-NH2] bind Hg-II and Cd-II in geometries that are different from what is normally found with thiol ligands in aqueous solution. A fundamental question has been whether this structural perturbation is due to protein influence or a change in the metal geometry preference. To address this question, we have completed linear free-energy analyses that correlate the association of three-stranded coiled coils in the absence of a metal with the binding affinity of the peptides to the heavy metals, Hg-II and CO. In this paper, six new members of this family have been synthesized, replacing core leucine residues with smaller and less hydrophobic residues, consequently leading to varying degrees of self-association affinities. At the same time, studies with some smaller and longer sequenced peptides have also been examined. All of these peptides are seen to sequester Hg-II and Cd-II in an uncommon trigonal environment. For both metals, the binding is strong with micromolar dissociation constants. For binding of Hg-II to the peptides, the dissociation constants range from 2.4 x 10(-5) M for Baby L12C to 2.5 x 10(-9) M for Grand L9C for binding of the third thiolate to a linear Hg-II(pep)2 species. The binding of Hg-II to the peptide Grand L9C is similar in energetics for metal binding in the metalloregulatory protein, mercury responsive (merR), displaying similar to 50 % trigonal HgII formation at nanomolar metal concentrations. Approximately, 11 kcal/mol of the Hg-II(Grand L9C)(3)(-) stability is due to peptide interactions, whereas only 1-4 kcal/mol stabilization results from Hg-II(RS)(2) binding the third thiolate ligand. This further validates the hypothesis that the favorable tertiary interactions in protein systems such as merR go a long way in stabilizing nonnatural coordination environments in biological systems. Similarly, for the binding of Cd-II to the TRI family, the dissociation constants range from 1.3 x 10(-6) M for Baby L9C to 8.3 x 10(-9) M for TRI L9C, showing a similar nature of stable aggregate formation.