Kinetics of trifurcated electron flow in the decaheme bacterial proteins MtrC and MtrF
Kinetics of trifurcated electron flow in the decaheme bacterial proteins MtrC and MtrF
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DOI：
10.1073/pnas.1818003116
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发表时间：
2019-02-26
影响因子：
11.1
通讯作者：
Blumberger, Jochen
中科院分区：
文献类型：
--
作者：
Jiang, Xiuyun;Burger, Bastian;Blumberger, Jochen
细菌希瓦氏菌oneidensis已经进化出一种复杂的电子转移（ET）机制，在细胞外呼吸过程中将电子从细胞质输出到细胞外空间。在这个过程的核心是十血红素蛋白的Mtr途径，MtrC和MtrF，位于外细菌膜的外表面。晶体结构显示，这些蛋白质结合10个c型血红素排列在一个交错的十字架，三叉的电子流的特殊形状，大概是为了减少细胞外底物，同时引导电子到相邻的多血红素细胞色素在任何一侧沿着膜。特别有趣的是设计的血红素结trifurcating电子流：它们是由共面和T形血红素对图案相对较大，似乎不利的隧穿距离。在这里，我们使用电子结构计算和分子模拟表明，血红素环的侧链，特别是插入在共面和T形血红素对之间的空间中的半胱氨酸连接，强烈增强这两个图案中的电子耦合。这导致在血红素连接处的ET步骤的大约10（3）倍加速，否则这将是速率限制。通过溶剂化蛋白质的预测的最大电子通量是非常相似的所有可能的流动方向，这表明MtrC和MtrF穿梭电子具有相似的效率和可逆的方向平行和正交的外膜。没有发现在ET特性的MtrC和MtrF的重大差异，这意味着在细胞外呼吸过程中的两种蛋白质的不同表达水平是不相关的氧化还原功能。
The bacterium Shewanella oneidensis has evolved a sophisticated electron transfer (ET) machinery to export electrons from the cytosol to extracellular space during extracellular respiration. At the heart of this process are decaheme proteins of the Mtr pathway, MtrC and MtrF, located at the external face of the outer bacterial membrane. Crystal structures have revealed that these proteins bind 10 c-type hemes arranged in the peculiar shape of a staggered cross that trifurcates the electron flow, presumably to reduce extracellular substrates while directing electrons to neighboring multiheme cytochromes at either side along the membrane. Especially intriguing is the design of the heme junctions trifurcating the electron flow: they are made of coplanar and T-shaped heme pair motifs with relatively large and seemingly unfavorable tunneling distances. Here, we use electronic structure calculations and molecular simulations to show that the side chains of the heme rings, in particular the cysteine linkages inserting in the space between coplanar and T-shaped heme pairs, strongly enhance electronic coupling in these two motifs. This results in an approximate to 10(3)-fold speedup of ET steps at heme junctions that would otherwise be rate limiting. The predicted maximum electron flux through the solvated proteins is remarkably similar for all possible flow directions, suggesting that MtrC and MtrF shuttle electrons with similar efficiency and reversibly in directions parallel and orthogonal to the outer membrane. No major differences in the ET properties of MtrC and MtrF are found, implying that the different expression levels of the two proteins during extracellular respiration are not related to redox function.