Direct Observation of Parallel Folding Pathways Revealed Using a Symmetric Repeat Protein System
Direct Observation of Parallel Folding Pathways Revealed Using a Symmetric Repeat Protein System
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DOI：
10.1016/j.bpj.2014.04.058
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发表时间：
2014-07-01
影响因子：
3.4
通讯作者：
Barrick, Doug
中科院分区：
文献类型：
--
作者：
Aksel, Tural;Barrick, Doug
虽然已经取得了进展，以确定从其一级结构的多肽的天然折叠，连接未折叠和折叠状态的途径的多样性还没有得到充分的探讨。理论和计算研究预测，蛋白质折叠通过漏斗状能量景观上的平行通路，尽管通路多样性的实验检测一直具有挑战性。在这里，我们利用线性重复蛋白质提供的高平移对称性和直接长度变化，通过平行途径直接检测折叠。通过比较的共识锚蛋白重复蛋白（CARP）的折叠速率，我们发现一个明显的增加折叠速率的大小和重复数的增加，虽然过渡态的大小（估计从变性剂的敏感性）保持不变。折叠速率随链长的增加而增加，而不是从球状蛋白的典型模型中预期的减少，这清楚地证明了平行途径。这一结论不依赖于广泛的曲线拟合或蛋白质结构的结构扰动。通过全局拟合一个简单的平行lsing路径模型，我们直接测量成核和蛋白质折叠的传播速率，并量化了通量沿着每个路径，提供了一个详细的能量景观折叠。这一发现的平行途径不同的结果从动力学研究的重复蛋白组成的序列可变重复，其中适度的重复能量变化合并成一个单一的，占主导地位的通道折叠。因此，对于在局部结构和拓扑结构中具有更高变化的球状蛋白，平行途径预计是例外而不是规则。
Although progress has been made to determine the native fold of a polypeptide from its primary structure, the diversity of pathways that connect the unfolded and folded states has not been adequately explored. Theoretical and computational studies predict that proteins fold through parallel pathways on funneled energy landscapes, although experimental detection of pathway diversity has been challenging. Here, we exploit the high translational symmetry and the direct length variation afforded by linear repeat proteins to directly detect folding through parallel pathways. By comparing folding rates of consensus ankyrin repeat proteins (CARPs), we find a clear increase in folding rates with increasing size and repeat number, although the size of the transition states (estimated from denaturant sensitivity) remains unchanged. The increase in folding rate with chain length, as opposed to a decrease expected from typical models for globular proteins, is a clear demonstration of parallel pathways. This conclusion is not dependent on extensive curve-fitting or structural perturbation of protein structure. By globally fitting a simple parallel-lsing pathway model, we have directly measured nucleation and propagation rates in protein folding, and have quantified the fluxes along each path, providing a detailed energy landscape for folding. This finding of parallel pathways differs from results from kinetic studies of repeat-proteins composed of sequence-variable repeats, where modest repeat-to-repeat energy variation coalesces folding into a single, dominant channel. Thus, for globular proteins, which have much higher variation in local structure and topology, parallel pathways are expected to be the exception rather than the rule.