Center for Biological NMR, Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA.
J Phys Chem B. 2011 Dec 29;115(51):15355-61. doi: 10.1021/jp206405b. Epub 2011 Dec 6.
Short, secondary-structure-containing peptides are suitable models for the study of protein folding due to their relative simplicity. Here, we investigate thermal denaturation of the tryptophan zipper peptide, trpzip4, a peptide that forms a β-hairpin in solution. In order to monitor the thermal denaturation of peptides or small proteins, chemical shift values of H(α) or H(N) may be used. However, various factors other than secondary structure can influence chemical shift values, such as side-chain orientation of nearby aromatic residues. Nuclear Overhauser effect (NOE) intensity from backbone interproton cross peaks is an alternative way to study thermal denaturation, as long as various factors that give rise to a change in NOE intensity upon changing the temperature are considered. As a relative indicator for denaturation, we define a cutoff temperature, where half of the initial NOE intensity is lost for each backbone interproton cross peak. For trpzip4, this cutoff temperature is highest for residues in the central part of the structure and lowest for residues near the termini. These observations support the notion that the structure of the trpzip4 peptide is stabilized by a hydrophobic cluster formed by tryptophan residues located in the central region of the β-hairpin.
短的、含有二级结构的肽是研究蛋白质折叠的合适模型，因为它们相对简单。在这里，我们研究了色氨酸拉链肽 trpzip4 的热变性，该肽在溶液中形成 β-发夹。为了监测肽或小蛋白的热变性，可以使用 H(α)或 H(N)的化学位移值。然而，除了二级结构之外，还有许多其他因素会影响化学位移值，例如附近芳香族残基的侧链取向。核 Overhauser 效应（NOE）强度来自骨架质子间交叉峰是研究热变性的另一种方法，只要考虑到导致温度变化时 NOE 强度发生变化的各种因素即可。作为变性的相对指标，我们定义了一个截止温度，对于每个骨架质子间交叉峰，初始 NOE 强度的一半在此温度下丢失。对于 trpzip4，结构中部残基的截止温度最高，末端附近残基的截止温度最低。这些观察结果支持了这样一种观点，即 trpzip4 肽的结构通过位于 β-发夹中心区域的色氨酸残基形成的疏水区簇稳定。
