Dynamics of one-state downhill protein folding
Dynamics of one-state downhill protein folding
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DOI：
10.1073/pnas.0802986106
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发表时间：
2009-01-06
影响因子：
11.1
通讯作者：
Munoz, Victor
中科院分区：
文献类型：
--
作者：
Li, Peng;Oliva, Fabiana Y.;Munoz, Victor
小螺旋蛋白 BBL 已被证明可以在没有自由能势垒的情况下折叠和展开，根据平衡实验中的一系列定量标准，包括探针依赖性平衡展开、变性剂之间的复杂耦合、特征 DSC 热分析图、二级结构的逐渐熔化以及跨越整个展开过程的逐个原子的异质展开行为。在这里，我们展示了通过 IR 探测主链结构和通过 FRET 探测端到端距离的纳秒 T 跳跃实验的结果。用这两种探针观察到的折叠动力学都是指数的，具有共同的弛豫时间，但在它们依赖于探针的平衡展开后，振幅存在很大差异。对两种探针的振幅和弛豫时间数据的定量分析表明，BBL 折叠动力学与一态折叠场景完全一致，并且与涉及一个或多个障碍穿越事件的替代模型不兼容。在 333 K 时，BBL 的弛豫时间为 1.3 μs，与之前的折叠速度极限估计一致。然而，室温下的晚期折叠事件要慢一个数量级（20μs），表明潜在的能量景观相对粗糙。我们在 BBL 中的结果揭示了单态折叠的动态特征，并绘制了折叠过程中构象运动的内在时间尺度。有趣的是，BBL 的简单自平均折叠动力学正是分子变阻器所需的动力学特性，从而支持单态折叠的生物学作用。
The small helical protein BBL has been shown to fold and unfold in the absence of a free energy barrier according to a battery of quantitative criteria in equilibrium experiments, including probe-dependent equilibrium unfolding, complex coupling between denaturing agents, characteristic DSC thermogram, gradual melting of secondary structure, and heterogeneous atom-by-atom unfolding behaviors spanning the entire unfolding process. Here, we present the results of nanosecond T-jump experiments probing backbone structure by IR and end-to-end distance by FRET. The folding dynamics observed with these two probes are both exponential with common relaxation times but have large differences in amplitude following their probe-dependent equilibrium unfolding. The quantitative analysis of amplitude and relaxation time data for both probes shows that BBL folding dynamics are fully consistent with the one-state folding scenario and incompatible with alternative models involving one or several barrier crossing events. At 333 K, the relaxation time for BBL is 1.3 mu s, in agreement with previous folding speed limit estimates. However, late folding events at room temperature are an order of magnitude slower ( 20 mu s), indicating a relatively rough underlying energy landscape. Our results in BBL expose the dynamic features of one-state folding and chart the intrinsic time-scales for conformational motions along the folding process. Interestingly, the simple self-averaging folding dynamics of BBL are the exact dynamic properties required in molecular rheostats, thus supporting a biological role for one-state folding.