Intrinsically disordered proteins (IDPs) usually fold during binding to target proteins. In contrast to interactions between folded proteins, this additional folding step makes the binding process more complex. Understanding the mechanism of coupled binding and folding of IDPs requires analysis of binding pathways that involve formation of the transient complex (TC). However, experimental characterization of TC is challenging because it only appears for a very brief period during binding. Here, we use single-molecule fluorescence spectroscopy to investigate the mechanism of diffusion-limited association of an IDP. A large enhancement of the association rate is observed due to the stabilization of TC by non-native electrostatic interactions. Moreover, photon-by-photon analysis reveals that the lifetime of TC for IDP binding is at least two orders of magnitude longer than that for binding of two folded proteins. This result suggests the long lifetime of TC is generally required for folding of IDPs during binding processes.

中文翻译：

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非天然静电相互作用对无序蛋白质的扩散限制。

本质上无序的蛋白质（IDP）通常在与目标蛋白质结合期间折叠。与折叠蛋白之间的相互作用相反，该额外的折叠步骤使结合过程更加复杂。了解IDP的结合结合和折叠机制需要分析涉及瞬时复合物（TC）形成的结合途径。但是，TC的实验表征具有挑战性，因为它在结合过程中只会出现很短的时间。在这里，我们使用单分子荧光光谱法研究IDP扩散受限的关联的机制。由于非天然静电相互作用使TC稳定，因此观察到缔合速率大大提高。而且，光子逐光子分析显示，IDP结合的TC寿命比两种折叠蛋白的结合的寿命至少长两个数量级。该结果表明，在结合过程中折叠IDP通常需要较长的TC寿命。