Proteins are insulating molecular solids, yet even those containing easily reduced or oxidized centers can have single-molecule electronic conductances that are too large to account for with conventional transport theories. Here, we report the observation of remarkably high electronic conductance states in an electrochemically-inactive protein, the ~200 kD αVβ3 extracelluar domain of human integrin. Large current pulses (up to nA) were observed for long durations (many ms, corresponding to many pC of charge transfer) at large gap (>5nm) distances in an STM when the protein was bound specifically by a small peptide ligand attached to the electrodes. The effect is greatly reduced when a homologous, weakly-binding protein (α4β1) is used as a control. In order to overcome the limitations of the STM, the time- and voltage-dependence of the conductance were further explored using a fixed-gap (5 nm) tunneling junction device that was small enough to trap a single protein molecule at any one time. Transitions to a high conductance (~ nS) state were observed, the protein being "on" for times from ms to tenths of a second. The high-conductance states only occur above ~ 100mV applied bias, and thus are not an equilibrium property of the protein. Nanoamp two-level signals indicate the specific capture of a single molecule in an electrode gap functionalized with the ligand. This offers a new approach to label-free electronic detection of single protein molecules. Electronic structure calculations yield a distribution of energy level spacings that is consistent with a recently proposed quantum-critical state for proteins, in which small fluctuations can drive transitions between localized and band-like electronic states.

中文翻译：

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蛋白质中巨大电导波动的观察。

蛋白质是绝缘的分子固体，但即使是那些含有易于还原或氧化的中心的蛋白质，其单分子电子电导也可能太大，无法用传统的运输理论来解释。在这里，我们报告了观察到的高电导率状态的电化学失活蛋白，人类整联蛋白的〜200 kDαVβ3胞外域。当STM蛋白质被附着在蛋白质上的小肽配体特异性结合时，在大间隙（> 5nm）距离上观察到了大电流脉冲（高达nA）了很长的时间（许多毫秒，相当于许多pC的电荷转移）。电极。当使用同源，弱结合蛋白（α4β1）作为对照时，效果会大大降低。为了克服STM的局限性，使用固定间隙（5 nm）的隧道结器件进一步探究了电导的时间和电压依赖性，该器件足够小，可以随时捕获单个蛋白质分子。观察到过渡到高电导（〜nS）状态，该蛋白质从毫秒到十分之一秒的时间处于“打开”状态。高电导状态仅在施加的偏置电压高于〜100mV时出现，因此不是蛋白质的平衡特性。纳安两级信号表明单个分子在配体功能化的电极间隙中的特异性捕获。这为单一蛋白质分子的无标记电子检测提供了一种新方法。电子结构计算得出的能级间距分布与最近提出的蛋白质的量子临界状态一致，