Rate enhancement of bacterial extracellular electron transport involves bound flavin semiquinones
Rate enhancement of bacterial extracellular electron transport involves bound flavin semiquinones
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DOI：
10.1073/pnas.1220823110
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发表时间：
2013-05-07
影响因子：
11.1
通讯作者：
Nakamura, Ryuhei
中科院分区：
文献类型：
--
作者：
Okamoto, Akihiro;Hashimoto, Kazuhito;Nakamura, Ryuhei
据推测，细胞外氧化还原活性化合物、黄素和其他醌在通过基于扩散的穿梭双电子转移机制将电子从细胞代谢系统传递到细胞外不溶性底物中发挥着重要作用。在这里，我们发现希瓦氏菌 MR-1 分泌的黄素分子增强了其外膜 c 型细胞色素 (OM c-Cyts) 作为氧化还原辅助因子传输电子的能力，但不增强游离形式的黄素。全细胞微分脉冲伏安法显示，黄素的氧化还原电位可逆地正向移动超过 100 mV，与微生物电流产生的增加非常一致。重要的是，这种黄素/OM c-Cyts 相互作用被发现可以促进通过半醌的单电子氧化还原反应，导致反应速率比游离黄素快 10(3) 至 10(5) 倍。这些结果与之前提出的氧化还原穿梭机制不一致，但表明黄素/OM c-Cyts 相互作用调节细胞外电子传递与细胞内代谢活动相结合的程度。
Extracellular redox-active compounds, flavins and other quinones, have been hypothesized to play a major role in the delivery of electrons from cellular metabolic systems to extracellular insoluble substrates by a diffusion-based shuttling two-electron-transfer mechanism. Here we show that flavin molecules secreted by Shewanella oneidensis MR-1 enhance the ability of its outer-membrane c-type cytochromes (OM c-Cyts) to transport electrons as redox cofactors, but not free-form flavins. Whole-cell differential pulse voltammetry revealed that the redox potential of flavin was reversibly shifted more than 100 mV in a positive direction, in good agreement with increasing microbial current generation. Importantly, this flavin/OM c-Cyts interaction was found to facilitate a one-electron redox reaction via a semiquinone, resulting in a 10(3)- to 10(5)-fold faster reaction rate than that of free flavin. These results are not consistent with previously proposed redox-shuttling mechanisms but suggest that the flavin/OM c-Cyts interaction regulates the extent of extracellular electron transport coupled with intracellular metabolic activity.