Kaleta David T, Jarrold Martin F
Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, USA.
J Am Chem Soc. 2003 Jun 18;125(24):7186-7. doi: 10.1021/ja0353006.
The conformations of unsolvated Ac-A14KG3A14K + 2H+ (Ac = acetyl, A = alanine, K = lysine, G = glycine) have been examined by ion mobility measurements and molecular dynamics simulations. This peptide was designed as a model helix-turn-helix motif. It was found to adopt three distinct geometries which were assigned to an extended helical conformation which is only stable at low temperatures (<230 K), a relatively high energy but metastable structure with exchanged lysines, and a coiled-coil. The coiled coil (which consists of an antiparallel arrangement of two helical alanine sections linked by a flexible glycine loop) is the dominant conformation. For temperatures >350 K, the experimental results indicate the helices uncouple and the loop randomizes. From equilibrium constants determined for this helix coupling right arrow over left arrow uncoupling transition, we found DeltaH degrees = -45 kJ mol-1 and DeltaS degrees = 114 J K-1 mol-1. -DeltaH degrees is essentially the enthalpy change for docking the two helices together while DeltaS degrees is essentially the entropy change for freeing up the glycine loop.
通过离子迁移率测量和分子动力学模拟研究了未溶剂化的乙酰化-A14KG3A14K + 2H⁺（Ac = 乙酰基，A = 丙氨酸，K = 赖氨酸，G = 甘氨酸）的构象。该肽被设计为一种模型螺旋-转角-螺旋基序。发现它采用三种不同的几何结构，分别被指定为仅在低温（<230 K）下稳定的伸展螺旋构象、具有交换赖氨酸的相对高能量但亚稳的结构以及卷曲螺旋。卷曲螺旋（由通过柔性甘氨酸环连接的两个螺旋丙氨酸部分的反平行排列组成）是主要构象。对于温度>350 K，实验结果表明螺旋解偶联且环随机化。根据为这种螺旋偶联⇌解偶联转变确定的平衡常数，我们发现ΔH° = -45 kJ mol⁻¹ 和ΔS° = 114 J K⁻¹ mol⁻¹。-ΔH°本质上是将两个螺旋对接在一起的焓变，而ΔS°本质上是释放甘氨酸环的熵变。
