Department of Chemistry, Haverford College 370 Lancaster Avenue, Haverford, Pennsylvania 19041-1392, USA.
J Phys Chem B. 2010 Apr 15;114(14):4931-6. doi: 10.1021/jp101447r.
Beta-thiocyanatoalanine, or cyanylated cysteine, is an artificial amino acid that can be introduced at solvent-exposed cysteine residues in proteins via chemical modification. Its facile post-translational synthesis means that it may find broad use in large protein systems as a probe of site-specific structure and dynamics. The C[triple bond]N stretching vibration of this artificial side chain provides an isolated infrared chromophore. To test both the perturbative effect of this side chain on local secondary structure and its sensitivity to structural changes, three variants of a model water-soluble alanine-repeat helix were synthesized containing cyanylated cysteine at different sites. The cyanylated cysteine side chain is shown to destabilize, but not completely disrupt, the helical structure of the folded peptide when substituted for alanine. In addition, the [triple bond]N stretching bandwidth of the artificial side chain is sensitive to the helix-coil structural transition. These model system results indicate that cyanylated cysteine can be placed into protein sequences with a native helical propensity without destroying the helix, and further that the CN probe may be able to report local helix formation events even when it is water-exposed in both the ordered and disordered conformational states. These results indicate that cyanylated cysteine could be a widely useful probe of structure-forming events in proteins with large in vitro structural distributions.
β-硫氰酸基丙氨酸，或硫氰酸化半胱氨酸，是一种人工氨基酸，可通过化学修饰将其引入蛋白质中溶剂暴露的半胱氨酸残基。其易于进行的翻译后合成意味着它可能在大型蛋白质系统中广泛用作特定位置结构和动态的探针。该人工侧链的 C[N 三重键]N 伸缩振动提供了一个孤立的红外发色团。为了测试该侧链对局部二级结构的微扰效应及其对结构变化的敏感性，我们合成了三种含有不同位置硫氰酸化半胱氨酸的模型水溶性丙氨酸重复螺旋的变体。当取代丙氨酸时，硫氰酸化半胱氨酸侧链被证明会使折叠肽的螺旋结构失稳，但不会完全破坏。此外，人工侧链的[N 三重键]N 伸缩带宽对螺旋-无规卷曲结构转变敏感。这些模型系统的结果表明，硫氰酸化半胱氨酸可以在不破坏螺旋的情况下被引入具有天然螺旋倾向的蛋白质序列中，并且进一步表明，即使在有序和无序构象状态下 CN 探针都能暴露于水中，该探针也可能能够报告局部螺旋形成事件。这些结果表明，硫氰酸化半胱氨酸可能是研究具有大体外结构分布的蛋白质中形成结构事件的一种广泛有用的探针。
