Department of Physics, Syracuse University, 201 Physics Building, Syracuse, New York 13244-1130, United States.
Structural Biology, Biochemistry, and Biophysics Program, Syracuse University, 111 College Place, Syracuse, New York 13244-4100, United States.
Langmuir. 2020 Dec 22;36(50):15247-15257. doi: 10.1021/acs.langmuir.0c02498. Epub 2020 Dec 13.
Previous studies of transmembrane protein channels have employed noise analysis to examine their statistical current fluctuations. In general, these explorations determined a substrate-induced amplification in the Gaussian white noise of these systems at a low-frequency regime. This outcome implies a lack of slowly appearing fluctuations in the number and local mobility of diffusing charges in the presence of channel substrates. Such parameters are among the key factors in generating a low-frequency 1/ noise. Here, we show that a protein-selective biological nanopore exhibits a substrate-induced amplification in the 1/ noise. The modular composition of this biological nanopore includes a hydrophilic transmembrane protein pore fused to a water-soluble binding protein on its extramembranous side. In addition, this protein nanopore shows an open substate populated by a high-frequency current noise because of the flickering of an engineered polypeptide adaptor at the tip of the pore. However, the physical association of the protein ligand with the binding domain reversibly switches the protein nanopore from a high-frequency noise substate into a quiet substate. In the absence of the protein ligand, our nanopore shows a low-frequency white noise. Remarkably, in the presence of the protein ligand, an amplified low-frequency 1/ noise was detected in a ligand concentration-dependent fashion. This finding suggests slowly occurring equilibrium fluctuations in the density and local mobility of charge carriers under these conditions. Furthermore, we report that the excess in 1/ noise is generated by reversible switches between the noisy ligand-released substate and the quiet ligand-captured substate. Finally, quantitative aspects of the low-frequency 1/ noise are in accord with theoretical predictions of the current noise analysis of protein channel-ligand interactions.
先前关于跨膜蛋白通道的研究运用噪声分析来研究它们的统计电流波动。一般来说，这些探索在低频范围内确定了基质诱导的这些系统中高斯白噪声的放大。这一结果意味着在通道基质存在的情况下，扩散电荷的数量和局部迁移率没有缓慢出现的波动。这些参数是产生低频 1/f 噪声的关键因素之一。在这里，我们表明，一种蛋白质选择性的生物纳米孔表现出基质诱导的 1/f 噪声放大。这种生物纳米孔的模块化组成包括亲水跨膜蛋白孔，其外膜侧融合有水溶性结合蛋白。此外，由于孔尖端的工程多肽接头的闪烁，这种蛋白质纳米孔显示出一个由高频电流噪声组成的开放亚态。然而，由于蛋白质配体与结合域的物理结合，蛋白质纳米孔可逆地从高频噪声亚态切换到安静亚态。在没有蛋白质配体的情况下，我们的纳米孔显示出低频白噪声。值得注意的是，在存在蛋白质配体的情况下，以配体浓度依赖的方式检测到放大的低频 1/f 噪声。这一发现表明，在这些条件下，载流子的密度和局部迁移率缓慢地出现平衡波动。此外，我们报告说，1/f 噪声的过剩是由嘈杂的配体释放亚态和安静的配体捕获亚态之间的可逆转换产生的。最后，低频 1/f 噪声的定量方面与蛋白质通道-配体相互作用的电流噪声分析的理论预测一致。
