Long-Lived Intermediates in a Cooperative Two-State Folding Transition
Long-Lived Intermediates in a Cooperative Two-State Folding Transition
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DOI：
10.1021/acs.jpcb.6b08932
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发表时间：
2016-12-01
影响因子：
3.3
通讯作者：
Clemmer, David E.
中科院分区：
文献类型：
--
作者：
El-Baba, Tarick J.;Kim, Doyong;Clemmer, David E.
生物分子折叠通常通过合作的二态反应物产物转变发生；合作一词并不表示中间结构不存在，而是表示这些状态无法通过现有的实验技术观察到。因此，很少有中间体被研究和表征。最近，离子迁移谱 (IMS) 测量表明，低聚物聚脯氨酸-13（Pro13，在丙醇 (PrOH) 中有利于形成具有顺式构型的相邻吡咯烷环的右手螺旋 PPI 结构）在转化为在水溶液中有利的全反式构型 PPII 结构时，会通过六个连续的长寿命中间体折叠。在这里，我们检查了 HisPro13 序列的 PPIPrOH -> PPIIaq 折叠转变，即 Pro13 在 N 末端添加了单个组氨酸残基。值得注意的是，IMS 测量结果表明，添加组氨酸后，所有与中间结构相关的 IMS 峰都消失了。相反，HisPro13 通过合作的两种状态转变折叠，并被显着的诱导期延迟。诱导期与温度相关——在较低温度下将转变时间延长。平衡研究表明，HisPro13 PPIProH -> PPIIaq 转变是吸热的，但有利于熵。根据这些线索，我们提出了一种顺序折叠机制，并开发了一个模型，该模型表明类似于 13-17 的长寿命中间体可能负责诱导期。在此模型中，中间体由类似于 90 kJ.mol(-1) 的平均单个激活势垒分隔，并且在熵上是有利的。
Biomolecular folding often occurs through a cooperative two-state reactant product transition; the term cooperative does not convey that intermediate structures are nonexistent but rather that these states are not observable by existing experimental techniques. Because of this, few intermediates have been studied and characterized. Recently, ion mobility spectrometry (IMS) measurements revealed that the oligomer polyproline-13 (Pro13, which in propanol (PrOH) favors the right-handed helical PPI structure having adjacent pyrrolidine rings in a cis configuration) folds through six sequential long-lived intermediates as it converts to the all-trans-configured PPII structure that is favored in aqueous solutions. Here, we examine the PPIPrOH -> PPIIaq folding transition for a HisPro13 sequence, i.e., Pro13 having a single histidine residue added to the N-terminus. Remarkably, the IMS measurements show that, upon addition of histidine, all of the IMS peaks associated with intermediate structures disappear. Instead, HisPro13 folds via a cooperative two-state transition, delayed by a significant induction period. The induction period is temperature dependent-shifting the transition to longer times at lower temperatures. Equilibrium studies show that the HisPro13 PPIProH -> PPIIaq transition is endothermic but favored entropically. From these clues, we propose a sequential folding mechanism and develop a model that suggests that similar to 13-17 long-lived intermediates are likely responsible for the induction period. In this model, intermediates are separated by average individual activation barriers of similar to 90 kJ.mol(-1), and are entropically favorable.