In this study we describe a new methodology to physically probe individual complexes formed between proteins and DNA. By combining nanoscale, high speed physical force measurement with sensitive fluorescence imaging we investigate the complex formed between the prokaryotic DNA repair protein UvrA2 and DNA. This approach uses a triangular, optically-trapped "nanoprobe" with a nanometer scale tip protruding from one vertex. By scanning this tip along a single DNA strand suspended between surface-bound micron-scale beads, quantum-dot tagged UvrA2 molecules bound to these '"DNA tightropes" can be mechanically interrogated. Encounters with UvrA2 led to deflections of the whole nanoprobe structure, which were converted to resistive force. A force histogram from all 144 detected interactions generated a bimodal distribution centered on 2.6 and 8.1 pN, possibly reflecting the asymmetry of UvrA2's binding to DNA. These observations successfully demonstrate the use of a highly controllable purpose-designed and built synthetic nanoprobe combined with fluorescence imaging to study protein-DNA interactions at the single molecule level.

译文

在这项研究中,我们描述了一种物理探测蛋白质和DNA之间形成的单个复合物的新方法。通过将纳米级,高速物理力测量与灵敏的荧光成像相结合,我们研究了原核DNA修复蛋白UvrA2与DNA之间形成的复合物。这种方法使用三角形的,光学捕获的 “纳米探针”,其纳米级尖端从一个顶点伸出。通过沿着悬浮在表面结合的微米级珠子之间的单个DNA链扫描该尖端,可以机械地询问与这些 “DNA牵索” 结合的量子点标记的UvrA2分子。与UvrA2的相遇导致整个纳米探针结构的偏转,并将其转换为阻力。来自所有144检测到的相互作用的力直方图产生了以2.6和8.1 pN为中心的双峰分布,这可能反映了UvrA2与DNA结合的不对称性。这些观察结果成功地证明了使用高度可控的目的设计和构建的合成纳米探针结合荧光成像技术在单分子水平上研究蛋白质-DNA相互作用。

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