Bacterial toxin-antitoxin system functionality and bacteriophage abortive infection: structure function and biology

细菌被称为噬菌体的特定病毒攻击和杀死。噬菌体是地球上最丰富的生物实体，它们的数量比它们的细菌宿主多10:1。尽管噬菌体数量过多，但这种细菌仍然无处不在，这是因为它们已经进化出了非凡的系统，可以防止病毒感染的潜在致命影响。这些保护性抗病毒系统中的一些在感染后被病毒激活，这一过程称为流产感染（Abi）。有超过20种已知的Abi系统被认为在病毒感染和复制过程的不同阶段起作用。我们在马铃薯软腐病的病原菌Erwinia中发现了一个由质粒编码的Abi系统。这个新的Abi系统通过两个组件工作；一种是对细菌细胞有毒的蛋白质（ToxN），另一种是在未感染条件下抑制毒素的RNA分子（ToxI），但是，当灭活时，会导致毒素的激活，最终导致细菌宿主细胞的程序性死亡。通过这种方式，被感染的细菌细胞“自杀”，一个重要的净效应是，病毒被困住了，不能被释放出来感染细菌种群的其他兄弟成员。因此，这一群体在某些单个细胞的病毒感染中存活下来，其行为类似于细菌的利他主义。我们已经证明，这种新的Abi系统在不同的细菌中起作用，并对许多不同的噬菌体作出反应。我们认为这种基于毒素-抗毒素（TA）的系统可能在控制病毒在环境中的传播以及细菌和噬菌体的进化中发挥重要作用。在这个项目中，我们试图剖析TA系统的作用机制。我们将确定能够杀死细菌的毒素（ToxN）的结构，并试图确定ToxI （RNA）分子如何抑制毒素的功能。我们还将研究毒素的结构与其生物学功能（终止噬菌体感染和杀死细菌细胞）之间的关系。我们将研究毒素的细胞靶标的性质。我们将研究能够避开毒素系统致命影响的突变病毒，通过研究这些突变，我们希望能够弄清楚噬菌体的哪些成分能够激活毒素系统。然后，我们将尝试人工表达特定的病毒成分，看看我们是否能开启抗病毒系统或利他自杀，杀死细菌。对噬菌体、细菌和抗病毒防御系统之间的相互作用进行更深层次的结构和机制理解，对于我们理解细菌的进化和适应（特别是对病毒攻击）非常重要。然而，除此之外，这项研究可能最终导致开发用于抗菌化疗的新型化学物质-新型抗生素。

Bacteria are attacked and killed by specific viruses called bacteriophages (phages). Phages are the most abundant biological entities on Earth and they outnumber their bacterial hosts by 10-1. Despite this superabundance of phages, the bacteria are still ubiquitous and this is because they have evolved remarkable systems to prevent the potentially lethal effects of viral infection. Some of these protective anti-viral systems are activated by the virus after infection in a process called abortive infection (Abi). There are over 20 known Abi systems which are thought to act at different stages in the viral infection and replication process. We discovered a new Abi system encoded by a plasmid in the bacterial plant pathogen, Erwinia - the causative agent of commercially significant potato soft rot disease. This new Abi system works via two components; one a protein (ToxN) that is toxic to the bacterial cell, and the other an RNA molecule (ToxI) that suppresses the toxin under uninfected conditions, but, when inactivated, leads to activation of the ToxN toxin, leading eventually to programmed death of the bacterial host cell. In this way, infected bacterial cells commit 'suicide' and an important net effect is that the virus is trapped and cannot be released to infect the other sibling members of the bacterial population. The group thus survives viral infection of some individual cells in a behavior akin to bacterial altruism. We have shown that this novel Abi system operates in different bacteria and in response to many different phages. We think that this Toxin-Antitoxin (TA) based system is likely to be important in controlling viral propagation in the environment, and for both bacterial and phage evolution. In this project we are trying to dissect the mechanism of action of the TA system. We will determine the structure of the toxin (ToxN) that can kill the bacteria and try to determine how the ToxI (RNA) molecule can suppress the function of the toxin. We will also study the relationship between the structure of the toxin and its biological function (in aborting phage infection and killing bacterial cells). We will investigate the nature of the cellular target(s) of the toxin. We will study mutant viruses that are able to get around the lethal effects of the ToxIN system and, by studying these mutants, we hope to be able to work out what components of the phage act to activate the ToxIN system. We will then try expressing the specific viral components artificially to see if we can switch on the antiviral system or altruistic suicide, to kill bacteria. Developing a deeper structural and mechanistic understanding of the interactions between phages, bacteria and the antiviral defence systems is important in our appreciation of evolution and adaptation of bacteria (particularly to viral attack). However, in addition, this research could lead eventually to the development of novel chemicals that have uses in antibacterial chemotherapy - new antibiotics.