Intrinsic electronic conductivity of individual atomically resolved amyloid crystals reveals micrometer-long hole hopping via tyrosines
Intrinsic electronic conductivity of individual atomically resolved amyloid crystals reveals micrometer-long hole hopping via tyrosines
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DOI：
10.1073/pnas.2014139118
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发表时间：
2021-01-12
影响因子：
11.1
通讯作者：
Malvankar, Nikhil S.
中科院分区：
文献类型：
--
作者：
Shipps, Catharine;Kelly, H. Ray;Malvankar, Nikhil S.
众所周知，蛋白质可以在几纳米的距离内转移电子。然而，许多生物过程需要电子传输更长的距离。例如，土壤和沉积物细菌通过富含芳香残基的假定丝状蛋白质传输电子，超过数百微米甚至厘米。然而，由于蛋白质和电极之间的大接触电阻，真实蛋白质电导率的测量受到人为因素的阻碍。使用单个淀粉样蛋白晶体的原子分辨率结构作为模型系统，我们进行无接触测量的固有电子电导率使用四电极的方法。我们发现空穴传输通过微米长的堆叠酪氨酸在生理相关的电位。值得注意的是，通过酪氨酸的转运速率（10（5）s（-1））与细胞色素相当。因此，我们的研究表明，淀粉样蛋白可以有效地传输电荷，在普通的热条件下，不需要任何氧化还原活性金属辅因子，大的驱动力，或光敏剂，以产生一个高氧化态的电荷注入。通过测量电导率作为分子长度，电压和温度的函数，同时消除接触电阻的主要贡献，我们表明，多步跳跃机制（由多个隧穿步骤组成），而不是单步隧穿，解释了测量的电导率。结合实验和计算的研究表明，质子耦合的电子转移赋予导电性;质子受体，相邻的谷氨酰胺，和它的接近酪氨酸的能量通过质子摇摆机制影响空穴传输速率。令人惊讶的是，电导率增加200倍，冷却后，由于更高的可用性质子受体通过增加氢键。
Proteins are commonly known to transfer electrons over distances limited to a few nanometers. However, many biological processes require electron transport over far longer distances. For example, soil and sediment bacteria transport electrons, over hundreds of micrometers to even centimeters, via putative filamentous proteins rich in aromatic residues. However, measurements of true protein conductivity have been hampered by artifacts due to large contact resistances between proteins and electrodes. Using individual amyloid protein crystals with atomic-resolution structures as a model system, we perform contact-free measurements of intrinsic electronic conductivity using a four-electrode approach. We find hole transport through micrometer-long stacked tyrosines at physiologically relevant potentials. Notably, the transport rate through tyrosines (10(5) s(-1)) is comparable to cytochromes. Our studies therefore show that amyloid proteins can efficiently transport charges, under ordinary thermal conditions, without any need for redox-active metal cofactors, large driving force, or photosensitizers to generate a high oxidation state for charge injection. By measuring conductivity as a function of molecular length, voltage, and temperature, while eliminating the dominant contribution of contact resistances, we show that a multistep hopping mechanism (composed of multiple tunneling steps), not single-step tunneling, explains the measured conductivity. Combined experimental and computational studies reveal that proton-coupled electron transfer confers conductivity; both the energetics of the proton acceptor, a neighboring glutamine, and its proximity to tyrosine influence the hole transport rate through a proton rocking mechanism. Surprisingly, conductivity increases 200-fold upon cooling due to higher availability of the proton acceptor by increased hydrogen bonding.