How do multi-heme cytochromes form transmembrane wires and conduct electrons between the cell and environment?

多血红素细胞色素如何形成跨膜线并在细胞和环境之间传导电子？

• 批准号: BB/H007288/1
• 负责人: Thomas Clarke
• 金额: $ 44.04万
• 依托单位: University of East Anglia
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FH007288%2F1
• 关键词: How; do; multi; heme; cytochromes

Humans obtain the energy they need for life by respiring ('breathing') oxygen. This process involves using electrons extracted from the food we eat to convert oxygen to water in a process known as oxygen reduction. Free energy is released in this process and we use this to make ATP, which is the universal energy currency of life. Our dependency on oxygen makes us obligate aerobes -take away the oxygen and we die. Thus humans are confined to living on the surface of planet Earth where oxygen is freely available. However, the vast proportion of Earth's habitable environments are not exploited by humans, but by a diversity of micro-organisms, including bacteria, that can live in the absence of oxygen. What is truly amazing is that some of these bacteria can live deep in the Earth's subsurface and survive by 'breathing rocks'. This is because some of the most abundant respiratory substrates in the Earth's subsurface environments are insoluble minerals, particularly minerals of iron. Such minerals give some soils a reddish colour and they can also be seen as red seams in exposed cliffs. In fact 'iron respiration' is amongst the most widespread respiratory process in anoxic zones and so has wide environmental significance. For example it directly impacts on the balance of several biogeochemical cycles such as the nitrogen, sulphur and carbon cycles and this can in turn influence the release of potent greenhouse gases, such as nitrous oxide. It can also be detrimental to the oil industry through contributing to the dissolution of subsurface or submarine oil pipes. In some aspects the way bacteria respire mineral iron is similar to the way in which they respire oxygen, using electrons to 'reduce' the respiratory substrate. Thus, electrons generated by metabolism inside the bacterial cell are passed to the iron, which changes its electronic state from a so-called 'ferric state' to a 'ferrous state' by the negatively charged electron. However, because the ferric iron mineral is a large insoluble particle it cannot freely diffuse into bacterial cells. Consequently, if a bacterium is to be able to utilise an iron mineral as a respiratory electron acceptor it must have a molecular answer to a perplexing question. 'How can the bacteria move electrons to the outside of the cell where the mineral is located when the electrons are generated by cellular metabolism inside the cell?' This is a very challenging problem for a so-called Gram negative bacteria since they are surrounded by two sealed cell membranes, the inner membrane and the outer membrane, and the insoluble mineral iron lies outside of this outer membrane. Part of the solution to the problem lies in special 'electron transfer proteins' that actually sit on the outside of the cell where they can pass electrons to extracellular insoluble minerals. However, this is not the whole solution, since there still needs to be a specialised electron transfer system to take the electrons across the outer membrane to mediate the passage of electrons out of the cell to these cell-surface proteins. The mechanism by which this electron transfer out of the cell to the so called 'microbe-mineral interface' occurs is still not known. It represents a major question in the study of the biochemistry of an environmentally abundant group of bacteria. Answering it will provide new insights into bacterial energetic processes. It will also have important biotechnological impacts since there is potential for using mineral oxide respiring bacteria in bioremediation processes for the clean up of environments contaminated with toxic organic pollutants (e.g. oil leaks) or radioactive metals, such as Uranium (VI). Their use in microbial fuel cells where the bacteria can be used to generate electric currents using electrodes as solid extracellular electron acceptors is also being explored.

人类通过呼吸氧气来获得生命所需的能量。这个过程涉及使用从我们吃的食物中提取的电子将氧气转化为水，这一过程称为氧气还原。在这个过程中释放出自由能，我们用它来制造ATP，这是生命的通用能量货币。我们对氧气的依赖使我们成为专性需氧菌--失去氧气，我们就会死亡。因此，人类只能生活在地球表面，那里的氧气是免费提供的。然而，地球上大部分的可居住环境并没有被人类利用，而是被包括细菌在内的各种微生物利用，这些微生物可以在没有氧气的情况下生存。真正令人惊讶的是，其中一些细菌可以生活在地球的地下深处，并通过“呼吸岩石”生存。这是因为地球地下环境中一些最丰富的呼吸基质是不溶性矿物，特别是铁矿物。这些矿物质使一些土壤呈红色，它们也可以在裸露的悬崖上看到红色的接缝。事实上，“铁呼吸”是缺氧区最广泛的呼吸过程之一，因此具有广泛的环境意义。例如，它直接影响氮、硫和碳循环等几个地球化学循环的平衡，这反过来又会影响一氧化二氮等强效温室气体的释放。它还可能通过促进地下或海底油管的溶解而对石油工业有害。在某些方面，细菌呼吸矿物铁的方式与它们呼吸氧气的方式相似，使用电子来“还原”呼吸底物。因此，细菌细胞内代谢产生的电子传递给铁，铁通过带负电荷的电子从所谓的“三价铁态”转变为“亚铁态”。但是，由于三价铁矿物是大的不溶性颗粒，它不能自由扩散到细菌细胞中。因此，如果细菌能够利用铁矿物作为呼吸电子受体，它必须对一个令人困惑的问题有一个分子答案。“当电子是由细胞内的细胞代谢产生时，细菌如何将电子转移到矿物质所在的细胞外？“对于所谓的革兰氏阴性细菌来说，这是一个非常具有挑战性的问题，因为它们被两个密封的细胞膜包围，内膜和外膜，而不溶性矿物铁位于外膜之外。解决这个问题的部分方法在于特殊的“电子转移蛋白”，它们实际上位于细胞外部，可以将电子传递给细胞外不溶性矿物质。然而，这并不是全部的解决方案，因为仍然需要一个专门的电子转移系统来将电子穿过外膜，以介导电子从细胞中传递到这些细胞表面蛋白。这种电子从细胞转移到所谓的“微生物-矿物质界面”的机制仍然未知。它代表了一个主要的问题，在生物化学研究的一组环境丰富的细菌。对它的研究将为细菌的能量过程提供新的见解。它还将产生重要的生物技术影响，因为有可能在生物补救过程中使用矿物氧化物呼吸细菌，以清理受有毒有机污染物（如漏油）或放射性金属（如铀（VI））污染的环境。它们在微生物燃料电池中的用途也在探索中，在微生物燃料电池中，细菌可以使用电极作为固体细胞外电子受体来产生电流。

项目成果

Redox Linked Flavin Sites in Extracellular Decaheme Proteins Involved in Microbe-Mineral Electron Transfer.

• DOI: 10.1038/srep11677
• 发表时间: 2015-07-01
• 期刊: Scientific reports
• 影响因子: 4.6
• 作者: Edwards MJ;White GF;Norman M;Tome-Fernandez A;Ainsworth E;Shi L;Fredrickson JK;Zachara JM;Butt JN;Richardson DJ;Clarke TA
• 通讯作者: Clarke TA

Rapid electron exchange between surface-exposed bacterial cytochromes and Fe(III) minerals

• DOI: 10.1073/pnas.1220074110
• 发表时间: 2013-04-16
• 期刊: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• 影响因子: 11.1
• 作者: White, Gaye F.;Shi, Zhi;Clarke, Thomas A.
• 通讯作者: Clarke, Thomas A.

Characterization of MtoD from Sideroxydans lithotrophicus: a cytochrome c electron shuttle used in lithoautotrophic growth.

• DOI: 10.3389/fmicb.2015.00332
• 发表时间: 2015
• 期刊: Frontiers in microbiology
• 影响因子: 5.2
• 作者: Beckwith CR;Edwards MJ;Lawes M;Shi L;Butt JN;Richardson DJ;Clarke TA
• 通讯作者: Clarke TA