How conformation matters: Ionic liquids as reaction media for oxidative folding and native chemical ligation of cysteine-containing peptides

考虑到离子液体在蛋白质和肽化学中的应用日益重要，表征离子对肽结构和以肽为反应物的反应的作用也很重要。本项目主要研究含半胱氨酸肽的氧化折叠和天然化学结扎（NCL）两种反应。在初步研究中，从海锥蜗牛中提取的结构紧凑的多种二硫桥接神经毒素被证明可以在生物相容性离子液体（例如[C2mim][OAc]， [C2mim][OTs]）中有效和正确地折叠成具有生物活性的构象。预成型的二级结构的稳定被认为是这种观察的原因。为了得到科学的解释，我们将对短、中型模型多肽以及天然富含cys的多肽进行离子液体介导的氧化折叠。通过光谱测量（例如CD和荧光光谱）的监测将提供对离子液体中肽的嵌入的见解。将改变反应条件，以建立单个肽折叠过程的优化，并探索是否有不同的参数影响肽稳定和二硫桥的形成。作为涉及半胱氨酸残基的第二种反应类型，离子液体中的NCL也将被研究。在这里，稳定和溶解作用对起始物质以及反应产物（小蛋白质，蛋白质结构域）都是决定合成结果的因素。因此，该项目将提供新的方法来获得含有半胱氨酸的肽和蛋白质，从而在生物学、生化和电生理学上对这些具有治疗潜力的复杂分子进行研究。

Concerning the increased significance of ionic liquids for applications in protein and peptide chemistry it is as well essential to characterize the ion effects on peptide structures and reactions involving peptides as reactants. This project is focused on studies of two reactions involving cysteine-containing peptides, oxidative folding and native chemical ligation (NCL). In preliminary studies structurally compact multiple disulfide-bridged neurotoxins derived from marine cone snails were shown to efficiently and correctly fold into their biologically active conformation in biocompatible ionic liquids (e.g. [C2mim][OAc], [C2mim][OTs]). Stabilization of pre-formed secondary structures by ILs was suggested to be the cause of this observation. In order to derive a scientific explanation, short and medium-sized model peptides as well as native Cys-rich peptides will be subjected to ionic liquid-mediated oxidative folding. Monitoring by spectroscopic measurements (e.g. CD, and fluorescence spectroscopy) will provide insights into embedment of the peptides in ionic liquids. Reaction conditions will be varied to establish optimization of individual peptide folding processes and to explore whether there are distinct parameter influencing peptide stabilization and disulfide bridge formation. As a second reaction type involving cysteine residues NCL will be investigated in ionic liquids, too. Here, stabilizing and solubilising effects on both, the starting material as well as the reaction products (small proteins, protein domains) is determining the synthetic outcome. The project will therefore provide new methodologies to obtain cysteinecontaining peptides and proteins in a scale enabling biological, biochemical and electrophysiological studies for such complex molecules carrying therapeutic potential.