Evaluating the involvement of tryptophan on thiolated peptide-mercury(II) complexes: Cation-pi interactions
Evaluating the involvement of tryptophan on thiolated peptide-mercury(II) complexes: Cation-pi interactions
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DOI：
10.1016/j.ica.2020.119552
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发表时间：
2020-06-01
影响因子：
2.8
通讯作者：
Nixon, Timothy
中科院分区：
文献类型：
--
作者：
Ngu-Schwemlein, Maria;Merle, John;Nixon, Timothy
了解汞（II）如何与含有辅助结合基团的双半胱氨酸肽形成复合物，可以为优化汞固定化提供重要见解。在这项研究中，我们研究了色氨酸如何参与肽-汞（II）复合物的形成。设计了由Cys-Xaa-Cys （CXC）序列组成的模型五肽，其中Xaa是Gly (Penta 1), Trp （Penta 2）和D-Trp （Penta 3）。通过光谱方法和分子模拟研究了它们与汞（II）的络合作用。紫外吸收差谱反映了双硫酸-汞（II）键的形成。这些光谱还显示了配合物形成后吲哚基团的B-b吸收带的变化。圆二色性（CD）光谱表明，汞（II）结合肽采用类似于I型β转结构的二级结构。汞（II）结合的Penta 2也在221 nm处形成负CD带，这表明色氨酸吲哚环与汞（II）之间通过阳离子- π相互作用存在关联。在等摩尔汞（II）存在下，Penta 2的荧光猝灭明显大于Penta 3。这些CD和荧光数据表明，Penta 3的吲哚环不与配位汞（II）相互作用。优化的1:1汞（II）肽结构表明，Penta 2的吲哚-pi系统参与汞（II）阳离子-pi相互作用，而Penta 3的吲哚-pi系统参与铵态阳离子-pi缔合。这些结构的见解将有助于设计更有效的汞螯合剂，其中包含色氨酸作为固定汞的辅助结合和疏水屏蔽基团（II）。
An understanding of how mercury(II) forms complexes with bis-cysteinyl peptides containing auxiliary binding groups could provide vital insights for optimal mercury immobilization. In this study, we investigate how tryptophan might participate in peptide-mercury(II) complex formation. Model pentapeptides consisting of a Cys-Xaa-Cys (CXC) sequence, where Xaa is Gly (Penta 1), Trp (Penta 2), and D-Trp (Penta 3) were designed. Their complexation with mercury(II) was studied by spectroscopic methods and molecular modeling. UV absorption difference spectra reflect the formation of bisthiolate-mercury(II) bonds. These spectra also show changes in the B-b absorption band of the indole group following complex formation. Circular Dichroism (CD) spectra indicate that mercury(II) bound peptides adopt a secondary structure resembling a type I beta turn structure. Mercury(II) bound Penta 2 also develops a negative CD band at 221 nm, which suggests an association between the tryptophan indole ring and mercury(II) via cation-pi interaction. Fluorescence quenching in the presence of equimolar mercury(II) is significantly greater for Penta 2 than Penta 3. These CD and fluorescence data indicate that the indole ring of Penta 3 is not interacting with the coordinated mercury(II). Optimized 1:1 mercury(II)-peptide structures show that the indole pi system of Penta 2 participates in mercury(II) cation-pi interaction, whereas in Penta 3 it is involved in ammonium cation-pi association. These structural insights will be useful for designing more effective mercury chelators containing tryptophan as an auxiliary binding and hydrophobic shielding group in immobilizing mercury(II).