Hauser Karin, Krejtschi Carsten, Huang Rong, Wu Ling, Keiderling Timothy A
Institut für Biophysik, Johann Wolfgang Goethe-Universität Frankfurt, Max-von-Laue-Strasse 1, 60438 Frankfurt, Germany.
J Am Chem Soc. 2008 Mar 12;130(10):2984-92. doi: 10.1021/ja074215l. Epub 2008 Feb 16.
Two antiparallel beta-strands connected by a turn make beta-hairpins an ideal model system to analyze the interactions and dynamics of beta-sheets. Site-specific conformational dynamics were studied by temperature-jump IR spectroscopy and isotopic labeling in a model based on the tryptophan zipper peptide, Trpzip2, developed by Cochran et al. (Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 5578). The modified Trpzip2C peptides have nearly identical equilibrium spectral behavior as Trpzip2 showing that they also form well-characterized beta-hairpin conformations in aqueous solution. Selective introduction of 13C=O groups on opposite strands lead to distinguishable cross-strand coupling of the labeled residues as monitored in the amide I' band. These frequency patterns reflect theoretical predictions, and the coupled 13C=O band loses intensity with increase in temperature and unfolding of the hairpin. Thermal relaxation kinetics were analyzed for unlabeled and cross-strand isotopically labeled variants. T-jumps of approximately 10 degrees C induce relaxation times of a few microseconds that decrease with increase of the peptide temperature. Differences in kinetic behavior for the loss of beta-strand and gain of disordered structure can be used to distinguish localized structure dynamics by comparison of nonlabeled and labeled amide I' components. Analysis of the data supports multistate dynamic and equilibrium behavior, but because of this process it is not possible to clearly define a folding and unfolding rate. Nonetheless, site-specific relaxation kinetics could be seen to be consistent with a hydrophobic collapse hypothesis for hairpin folding.
由一个转角连接的两条反向平行β链使β-发夹成为分析β-折叠片层相互作用和动力学的理想模型系统。通过温度跃升红外光谱和同位素标记，在基于Cochran等人（《美国国家科学院院刊》2001年，98卷，5578页）开发的色氨酸拉链肽Trpzip2的模型中研究了位点特异性构象动力学。修饰后的Trpzip2C肽具有与Trpzip2几乎相同的平衡光谱行为，表明它们在水溶液中也形成了特征明确的β-发夹构象。在相反链上选择性引入13C=O基团会导致标记残基在酰胺I'带中监测到可区分的跨链偶联。这些频率模式反映了理论预测，并且随着温度升高和发夹展开，偶联的13C=O带强度降低。对未标记和跨链同位素标记变体的热弛豫动力学进行了分析。大约10℃的温度跃升诱导了几微秒的弛豫时间，该时间随着肽温度的升高而降低。β链丢失和无序结构增加的动力学行为差异可用于通过比较未标记和标记的酰胺I'组分来区分局部结构动力学。数据分析支持多态动态和平衡行为，但由于这个过程，不可能明确界定折叠和展开速率。尽管如此，位点特异性弛豫动力学可以被视为与发夹折叠的疏水塌缩假说是一致的。
