Huang Rong, Wu Ling, McElheny Dan, Bour Petr, Roy Anjan, Keiderling Timothy A
Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois 60607-7061, USA.
J Phys Chem B. 2009 Apr 23;113(16):5661-74. doi: 10.1021/jp9014299.
Conformational properties of a 12-residue tryptophan zipper (trpzip) beta-hairpin peptide (AWAWENGKWAWK-NH(2), a modification of the original trpzip2 sequence) are analyzed under equilibrium conditions using ECD and IR spectra of a series of variants, singly and doubly C(1)-labeled with (13)C on the amide CO. The characteristic features of the (13)CO component of the amide I' IR band and their sensitivity to the local structure of the peptide are used to differentiate stabilities for parts of the hairpin structure. Doubly labeled peptide spectra indicate that the ends of the beta-strands are frayed and that the center part is more stable as would be expected from formation of a stable hydrophobic core consisting of four tryptophan residues, and supported by MD simulations. NMR analyses were used to determine a best fit solution structure that is in close agreement with that of trpzip2, except for a small variation in the turn geometry. The distinct vibrational coupling patterns of the labeled sites based on this structure are also well matched by ab initio DFT-level calculations of their IR spectral patterns. Thermal unfolding of the peptides as studied with CD spectra could be fit with an apparent two-state transition model. ECD senses only the tryptophan interactions (tertiary-like) and their overall environment, as shown by TD-DFT modeling of the Trp-Trp pi-pi ECD. However, variation of the amide I IR spectra of (13)C-isotopomers showed that the thermal unfolding process is not cooperative in terms of the peptide backbone (secondary structure), since the transition temperatures sensed for labeled modes differ from those for the whole peptide. The thermal data also evidence dependence on concentration and pH but these cause little spectral variation. This study illustrates the consequences of multistate conformational change at the residue- or sequence-specific level in a system whose structure is dominated by hydrophobic collapse.
在平衡条件下，使用一系列酰胺羰基（CO）上单重和双重C(1)标记的(13)C同位素变体的ECD和IR光谱，分析了一种12残基色氨酸拉链（trpzip）β-发夹肽（AWAWENGKWAWK-NH(2)，原始trpzip2序列的一种修饰）的构象性质。酰胺I' IR带的(13)CO组分的特征及其对肽局部结构的敏感性，用于区分发夹结构各部分的稳定性。双重标记肽的光谱表明，β-链的末端是松散的，而中心部分更稳定，这正如由四个色氨酸残基形成稳定疏水核心所预期的那样，并且得到了分子动力学模拟的支持。NMR分析用于确定一个最佳拟合的溶液结构，该结构与trpzip2的结构非常吻合，只是在转角几何结构上有小的变化。基于此结构的标记位点独特的振动耦合模式，也与它们的IR光谱模式的从头算DFT水平计算很好地匹配。用CD光谱研究的肽的热解折叠可以用一个表观的两态转变模型来拟合。ECD仅感知色氨酸相互作用（类似三级结构）及其整体环境，如Trp-Trp π-π ECD的TD-DFT建模所示。然而，(13)C-同位素异构体的酰胺I IR光谱变化表明，就肽主链（二级结构）而言，热解折叠过程不是协同的，因为标记模式所感知的转变温度与整个肽的不同。热数据也证明了对浓度和pH的依赖性，但这些引起的光谱变化很小。这项研究说明了在一个结构由疏水塌缩主导的系统中，残基或序列特异性水平上多态构象变化的后果。
