Department of Chemistry , Duke University , Durham , North Carolina 27708 , United States.
Department of Biochemistry , Duke University , Durham , North Carolina 27710 , United States.
J Phys Chem B. 2019 Jun 20;123(24):5035-5047. doi: 10.1021/acs.jpcb.9b01086. Epub 2019 Jun 10.
The electrically conductive pili of Geobacter sulfurreducens are of both fundamental and practical interest. They facilitate extracellular and interspecies electron transfer (ET) and also provide an electrical interface between living and nonliving systems. We examine the possible mechanisms of G. sulfurreducens electron transfer in regimes ranging from incoherent to coherent transport. For plausible ET parameters, electron transfer in G. sulfurreducens bacterial nanowires mediated only by the protein is predicted to be dominated by incoherent hopping between phenylalanine (Phe) and tyrosine (Tyr) residues that are 3 to 4 Å apart, where Phe residues in the hopping pathways may create delocalized "islands." This mechanism could be accessible in the presence of strong oxidants that are capable of oxidizing Phe and Tyr residues. We also examine the physical requirements needed to sustain biological respiration via nanowires. We find that the hopping regimes with ET rates on the order of 10 s between Phe islands and Tyr residues, and conductivities on the order of mS/cm, can support ET fluxes that are compatible with cellular respiration rates, although sustaining this delocalization in the heterogeneous protein environment may be challenging. Computed values of fully coherent electron fluxes through the pili are orders of magnitude too low to support microbial respiration. We suggest experimental probes of the transport mechanism based on mutant studies to examine the roles of aromatic amino acids and yet to be identified redox cofactors.
导电菌毛在希瓦氏菌属中的作用兼具基础科学和实际应用价值。它们促进了细胞外和种间电子转移（ET），并为活细胞和非活细胞系统之间提供了电接口。我们研究了希瓦氏菌属在从非相干到相干输运的不同条件下电子转移的可能机制。对于合理的 ET 参数，仅由蛋白质介导的希瓦氏菌属细菌纳米线中的电子转移预计将由相隔 3 到 4 Å 的苯丙氨酸（Phe）和酪氨酸（Tyr）残基之间的非相干跳跃主导，其中跳跃途径中的 Phe 残基可能会产生非定域的“岛屿”。这种机制在能够氧化 Phe 和 Tyr 残基的强氧化剂存在下可能是可行的。我们还研究了通过纳米线维持生物呼吸所需的物理要求。我们发现，在 Phe 岛和 Tyr 残基之间 ET 速率约为 10 s，电导率约为 mS/cm 的跳跃区域，可以支持与细胞呼吸速率兼容的 ET 通量，尽管在异质蛋白环境中维持这种离域可能具有挑战性。通过菌毛进行完全相干电子流的计算值低得离谱，无法支持微生物呼吸。我们建议根据突变体研究来进行实验探测，以检验芳香族氨基酸和尚未确定的氧化还原辅因子的作用。
