Effect of viscosity on the kinetics of α-helix and β-hairpin formation
Effect of viscosity on the kinetics of α-helix and β-hairpin formation
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DOI：
10.1021/jp0022048
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发表时间：
2001-01-11
影响因子：
3.3
通讯作者：
Hofrichter, J
中科院分区：
文献类型：
--
作者：
Jas, GS;Eaton, WA;Hofrichter, J
纳秒激光温度跳跃和荧光检测用于测量粘度对含有21和16个氨基酸的肽中β-螺旋和β-发夹形成动力学的影响。分别通过添加浓度不显著改变平衡解折叠曲线的葡萄糖和蔗糖来改变溶剂粘度。在固定的溶剂组合物的温度依赖性的分析表明，活化能也不受影响，表明在添加糖的结果完全从他们的动态效应的增加溶剂粘度（η）的弛豫速率减慢。发现β-发夹形成的速率几乎如Kramers理论在高摩擦极限中所预测的那样变化为1/eta。相反，α-螺旋形成的速率表现出分数粘度依赖性（k = eta（-α）），指数α近似为0.6.用一个简单的统计力学模型得到的旋转一对骨架二面角的基本动力学步骤的内禀活化能，对于β-发夹结构接近于零，而对于α-螺旋结构则接近于5千卡/摩尔。如果较高的势垒频率可以与较大的活化能相关联，则α-螺旋的分数粘度依赖性可能是由于跨越势垒顶部的运动快于溶剂弛豫时间的事实。
Nanosecond laser temperature jumps and fluorescence detection were used to measure the effect of viscosity on the kinetics of beta -helix and beta -hairpin formation in peptides containing 21 and 16 amino acids. respectively. The solvent viscosity was changed by adding glucose and sucrose at concentrations that do not significantly alter the equilibrium unfolding curves. Analysis of the temperature dependence at fixed solvent compositions shows that the activation energies are also unaffected, indicating that the slowing of the relaxation rates upon addition of the sugars results entirely from their dynamical effect of increasing the solvent viscosity (eta). The rate of beta -hairpin formation was found to vary nearly as 1/eta, as predicted by Kramers theory in the high friction limit. In contrast, the rate of alpha -helix formation exhibited a fractional viscosity dependence (k = eta (-alpha)) with an exponent alpha approximate to 0.6. The intrinsic activation energy for the elementary kinetic step of rotating a pair of backbone dihedral angles, obtained using a simple statistical mechanical model, is near zero for the beta -hairpin but is similar to5 kcal/mol for the alpha -helix. If a higher barrier frequency can be associated with the larger activation energy, the fractional viscosity dependence for the alpha -helix may result from the fact that motion across the barrier top is faster than the solvent relaxation time.