Centre for Molecular and Structural Biochemistry, School of Biological Sciences and School of Chemistry, University of East Anglia, Norwich NR4 7TJ, United Kingdom.
Proc Natl Acad Sci U S A. 2011 Jun 7;108(23):9384-9. doi: 10.1073/pnas.1017200108. Epub 2011 May 23.
Some bacterial species are able to utilize extracellular mineral forms of iron and manganese as respiratory electron acceptors. In Shewanella oneidensis this involves decaheme cytochromes that are located on the bacterial cell surface at the termini of trans-outer-membrane electron transfer conduits. The cell surface cytochromes can potentially play multiple roles in mediating electron transfer directly to insoluble electron sinks, catalyzing electron exchange with flavin electron shuttles or participating in extracellular intercytochrome electron exchange along "nanowire" appendages. We present a 3.2-Å crystal structure of one of these decaheme cytochromes, MtrF, that allows the spatial organization of the 10 hemes to be visualized for the first time. The hemes are organized across four domains in a unique crossed conformation, in which a staggered 65-Å octaheme chain transects the length of the protein and is bisected by a planar 45-Å tetraheme chain that connects two extended Greek key split β-barrel domains. The structure provides molecular insight into how reduction of insoluble substrate (e.g., minerals), soluble substrates (e.g., flavins), and cytochrome redox partners might be possible in tandem at different termini of a trifurcated electron transport chain on the cell surface.
一些细菌物种能够利用细胞外的矿物质形式的铁和锰作为呼吸电子受体。在希瓦氏菌属（Shewanella oneidensis）中，这涉及位于跨外膜电子传递管道末端的十联体细胞色素，这些细胞色素位于细菌细胞表面。细胞表面细胞色素在介导电子直接转移到不溶性电子汇、催化与黄素电子穿梭体的电子交换或参与细胞外细胞色素间电子交换方面，具有潜在的多种作用，沿“纳米线”附属物。我们展示了其中一种十联体细胞色素 MtrF 的 3.2 Å 晶体结构，这使得首次能够可视化 10 个血红素的空间组织。血红素在四个结构域中以独特的交叉构象组织，交错的 65 Å 八联体链穿过蛋白质的长度，并由一个平面的 45 Å 四联体链平分，该四联体链连接两个扩展的希腊键分裂的β桶结构域。该结构为理解如何在细胞表面的三叉电子传递链的不同末端上串联实现不溶性底物（例如矿物质）、可溶性底物（例如黄素）和细胞色素氧化还原伴侣的还原提供了分子见解。
