Polymer scaling laws of unfolded and intrinsically disordered proteins quantified with single-molecule spectroscopy
Polymer scaling laws of unfolded and intrinsically disordered proteins quantified with single-molecule spectroscopy
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DOI：
10.1073/pnas.1207719109
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发表时间：
2012-10-02
影响因子：
11.1
通讯作者：
Schuler, Benjamin
中科院分区：
文献类型：
--
作者：
Hofmann, Hagen;Soranno, Andrea;Schuler, Benjamin
未折叠和内在无序的蛋白质的尺寸高度依赖于它们的氨基酸组成和溶液条件，特别是盐和变性剂的浓度。然而，这种行为的定量含义仍然不清楚，很大程度上是因为有效的theta状态，即潜在聚合物崩溃转变的中心参考点，无法通过实验确定。在这里，我们使用单分子荧光光谱和双焦点相关光谱来确定六种不同蛋白质的θ点。虽然在高变性剂浓度下，所有蛋白质的结垢指数收敛于0.62 +/- 0.03，正如聚合物在良好溶剂中的预期那样，但在水中的结垢制度强烈依赖于序列组成。本研究中四个可折叠蛋白序列的平均缩放指数为0.46 +/- 0.05，表明水细胞环境接近于未折叠蛋白的有效theta条件。相比之下，两种内在无序的蛋白质在任何溶剂条件下都没有达到t点，这可能反映了它们与细胞伴侣相互作用的扩展状态的优化。基于我们的结果的序列分析表明，具有更紧凑的未折叠状态的可折叠序列是蛋白质进化的最新结果。
The dimensions of unfolded and intrinsically disordered proteins are highly dependent on their amino acid composition and solution conditions, especially salt and denaturant concentration. However, the quantitative implications of this behavior have remained unclear, largely because the effective theta-state, the central reference point for the underlying polymer collapse transition, has eluded experimental determination. Here, we used single-molecule fluorescence spectroscopy and two-focus correlation spectroscopy to determine the theta points for six different proteins. While the scaling exponents of all proteins converge to 0.62 +/- 0.03 at high denaturant concentrations, as expected for a polymer in good solvent, the scaling regime in water strongly depends on sequence composition. The resulting average scaling exponent of 0.46 +/- 0.05 for the four foldable protein sequences in our study suggests that the aqueous cellular milieu is close to effective theta conditions for unfolded proteins. In contrast, two intrinsically disordered proteins do not reach the T-point under any of our solvent conditions, which may reflect the optimization of their expanded state for the interactions with cellular partners. Sequence analyses based on our results imply that foldable sequences with more compact unfolded states are a more recent result of protein evolution.