Fast electron transfer through a single molecule natively structured redox protein
Fast electron transfer through a single molecule natively structured redox protein
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DOI：
10.1039/c2nr32131a
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发表时间：
2012-01-01
期刊：
影响因子：
6.7
通讯作者：
Elliott, Martin
中科院分区：
文献类型：
--
作者：
Della Pia, Eduardo Antonio;Chi, Qijin;Elliott, Martin
蛋白质的电子转移特性通常以分子平均集合来测量。通过这些和相关的测量，蛋白质被广泛认为是宏观绝缘材料。利用扫描隧道显微镜（STM），我们提出了新的测量电导通过单分子的电子转移蛋白细胞色素B（562）在其天然构象，在伪生理条件下。这是通过蛋白质工程在分子的相对末端处的硫醇（SH）连接体对实现的，从而在金表面和铂铱STM尖端之间产生限定的共价接触。两种不同的方向的接头进行了检查：长轴配置（SH-LA）和短轴配置（SH-SA）。在每种情况下，分子电导都可以通过血红素氧化还原状态的电化学控制来“门控”。在这个相对复杂的电子转移系统中观察到可再现的和显著高的电导，对于接近零电化学过电位的SH-SA和SH-LA细胞色素B（562）分子，单分子电导值峰值约为18 nS和12 nS。这有力地指出了血红素辅因子与天然结构蛋白质结合的重要作用。我们建议，在STM几何结构中的蛋白质电子转移的两步模型需要一个多电子转移来解释这样高的电导。该模型还产生了重组能量的低值，这意味着溶剂重组基本上是不存在的。
The electron transfer properties of proteins are normally measured as molecularly averaged ensembles. Through these and related measurements, proteins are widely regarded as macroscopically insulating materials. Using scanning tunnelling microscopy (STM), we present new measurements of the conductance through single-molecules of the electron transfer protein cytochrome b(562) in its native conformation, under pseudo-physiological conditions. This is achieved by thiol (SH) linker pairs at opposite ends of the molecule through protein engineering, resulting in defined covalent contact between a gold surface and a platinum-iridium STM tip. Two different orientations of the linkers were examined: a long-axis configuration (SH-LA) and a short-axis configuration (SH-SA). In each case, the molecular conductance could be 'gated' through electrochemical control of the heme redox state. Reproducible and remarkably high conductance was observed in this relatively complex electron transfer system, with single-molecule conductance values peaking around 18 nS and 12 nS for the SH-SA and SH-LA cytochrome b(562) molecules near zero electrochemical overpotential. This strongly points to the important role of the heme co-factor bound to the natively structured protein. We suggest that the two-step model of protein electron transfer in the STM geometry requires a multi-electron transfer to explain such a high conductance. The model also yields a low value for the reorganisation energy, implying that solvent reorganisation is largely absent.