Studies of helix fraying and solvation using 13C′ isotopomers
Studies of helix fraying and solvation using 13C′ isotopomers
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DOI：
10.1110/ps.051510705
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发表时间：
2005-09-01
期刊：
影响因子：
8
通讯作者：
Andersen, NH
中科院分区：
文献类型：
--
作者：
Fesinmeyer, RM;Peterson, ES;Andersen, NH
设计的螺旋的羰基（13 C '）同位素异构体的NMR和IR研究都可以提供关于沿着螺旋肽序列的螺旋phi/psi角沿着的分数出现和熔融行为的残余水平细节，这些细节不能从CD或H-1-NMR研究中获得。我们研究了一系列经典的螺旋模型Ac-YGG-（KAXAA）（3）K-NH_2（X = A，V），在含有氟醇共溶剂的水溶液和有利于螺旋的介质中，包括允许观察冷变性的溶剂系统。这些研究证实了与该序列相关的强N-加帽，并揭示了比使用当前螺旋度预测算法计算的更广泛的C-末端磨损。在X = A系列中，中心残基对热熔融有一定的抵抗力;相反，它主要发生在可磨损的C末端。对于在冷变性条件下的X = V系列，最大螺旋度的温度沿着序列是不均匀的，并且溶剂化和非溶剂化螺旋丙氨酸位点（分别在1592 cm（-1）和1615 cm（-1）处的C-13 = 0延伸）是明显的。所采用的两种光谱之间的相关性产生了有趣的观察结果，即缬氨酸侧链能够使短单体螺旋中的i - 4酰胺去溶剂化。此外，我们报告的丙氨酸统计线圈化学位移的温度依赖性的进一步测量，尿素的C-13化学位移的温度依赖性（用作化学位移参考），和一个有用的公式转换C-13，移位成分数螺旋。
Both NMR and IR studies of carbonyl (13C') isotoporners of designed helices can provide residue-level details regarding the fractional occurrence and melting behavior of helical phi/psi angles along the sequence of helical peptides, details that cannot be obtained from CD or H-1-NMR studies. We have studied a classic series of helical models, Ac-YGG-(KAXAA)(3)K-NH2 (X = A,V), in both aqueous and helix-favoring media containing fluoroalcohol cosolvents, including a solvent system allowing the observation of cold denaturation. These studies confirmed the strong N-capping associated with this sequence and revealed more extensive C-terminal fraying than that calculated using current helicity prediction algorithms. In the X = A series, the central residues are somewhat resistant to thermal melting; it instead occurs predominantly at the frayable C terminus. For the X = V series under cold-denaturing conditions, the temperature of maximal helicity is not uniform along the sequence and both solvated and nonsolvated helical alanine sites (C-13 = 0 stretches at 1592 cm(-1) and 1615 cm(-1), respectively) are apparent. Correlation between the two spectroscopies employed yielded the intriguing observation that the valine side chain is able to desolvate the i - 4 amide in short monomeric helices. In addition, we report further measurements of the temperature dependence of alanine statistical coil chemical shifts, the temperature dependence of the C-13 chemical shift of urea (employed as chemical shift reference), and a useful formula for converting C-13, shifts into fractional helicities.