Heme Hopping Falls Short: What Explains Anti-Arrhenius Conductivity in a Multi-heme Cytochrome Nanowire?
Heme Hopping Falls Short: What Explains Anti-Arrhenius Conductivity in a Multi-heme Cytochrome Nanowire?
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DOI：
10.1101/2022.08.01.502099
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发表时间：
2022-08
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通讯作者：
Matthew J. Guberman‐Pfeffer
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作者：
Matthew J. Guberman‐Pfeffer
外膜细胞色素类型S（OmcS）的螺旋均聚物被提出用于将常见的土壤细菌Geophylsulfurreducens与矿物和其他微生物电连接，以进行重要的地球化学过程。OmcS表现出一个令人惊讶的上升，电导率冷却后，从300至270 K，最近已被归因于重组的H-键，这反过来又调制血红素氧化还原电位。本文通过（1）在涵盖整个实验范围的13个温度下分析氢键;（2）用量子力学/分子力学计算从3倍长（2 μs）的分子动力学以及3 μs的恒定氧化还原和pH分子动力学采样的10倍多（3000）构型的氧化还原电势;（3）用单粒子扩散和多粒子通量动力学方案模拟氧化还原导电。在冷却30 K时，蛋白质内氢键网络的连接是高度相似的（86%）。丝水合壳的密度和静态介电常数的增加导致血红素氧化还原电位的−0.002 V/K偏移，电荷迁移率降低2倍。修正了先前工作中过负的氧化还原电位（−0.521 V;预期= −0.350 - +0.150 V;新计算值）。= −0.214 V vs. SHE）导致迁移率在高温下比低温下更大，与最初的预测相反。这些溶液相氧化还原传导模型未能再现电极吸收，部分脱水，并可能聚集的OmcS丝的实验电导率。通过忽略从溶剂到模型脱水的重组能，可以看到一些改进。正确的建模的物理状态的建议是一个先决条件，达到一个判决的操作电荷传输机制和其温度响应的分子基础。
A helical homopolymer of the outer-membrane cytochrome type S (OmcS) was proposed to electrically connect a common soil bacterium, Geobacter sulfurreducens, with minerals and other microbes for biogeochemically important processes. OmcS exhibits a surprising rise in conductivity upon cooling from 300 to 270 K that has recently been attributed to a restructuring of H-bonds, which in turn modulates heme redox potentials. This proposal is more thoroughly examine herein by (1) analyzing H-bonding at 13 temperatures encompassing the entire experimental range; (2) computing redox potentials with quantum mechanics/molecular mechanics for 10-times more (3000) configurations sampled from 3-times longer (2 μs) molecular dynamics, as well as 3 μs of constant redox and pH molecular dynamics; and (3) modeling redox conduction with both single-particle diffusion and multi-particle flux kinetic schemes. Upon cooling by 30 K, the connectivity of the intra-protein H-bonding network was highly (86%) similar. An increase in the density and static dielectric constant of the filament’s hydration shell caused a −0.002 V/K shift in heme redox potentials, and a factor of 2 decrease in charge mobility. Revision of a too-far negative redox potential in prior work (−0.521 V; expected = −0.350 – +0.150 V; new Calc. = −0.214 V vs. SHE) caused the mobility to be greater at high versus low temperature, opposite to the original prediction. These solution-phase redox conduction models failed to reproduce the experimental conductivity of electrode-absorbed, partially dehydrated, and possibly aggregated OmcS filaments. Some improvement was seen by neglecting reorganization energy from the solvent to model dehydration. Correct modeling of the physical state is suggested to be a prerequisite for reaching a verdict on the operative charge transport mechanism and the molecular basis of its temperature response.