Dissecting the Molecular Biology of Cyclic Oligoadenylate Signalling

就像人类一样，细菌有一个复杂的免疫系统来保护它们免受病毒的感染。CRISPR系统在细菌中提供适应性免疫，类似于我们的抗体系统。对公众来说，CRISPR通常是Cas9酶的同义词，Cas9酶使基因组编辑技术取得了快速进展。然而，Cas9（一种II型CRISPR系统）在微生物中相当罕见，微生物中更常见的是I型或III型CRISPR系统。最近，研究III型CRISPR的科学家发现了一种新的信号分子，环低聚腺苷酸（cOA），它是由细胞中的主要能量分子ATP构建的。cOA在暴露于病毒的细胞中发出感染状态的信号，调动细胞的防御能力。我们只知道这种防御的一个方面——一种咀嚼RNA的酶，叫做Csm6。它似乎为细胞争取了一些时间来帮助清除感染，但如果细胞不能摆脱病毒，也可能导致细胞“自杀”。通过研究不同细菌中的CRISPR系统，我们发现了两种新的细胞防御酶，它们被辅酶a信号激活来降解病毒遗传物质。我们还发现了一种由病毒产生的酶，它可以迅速分解辅酶a——它可能起到“抗crispr”的作用，关闭细胞的防御。我们想了解这三种酶是如何与辅酶a结合的，它们是如何呈现活性形状的，以及它们在体外（在试管中）和体内（在细胞中）做什么。这项工作将为我们对重要的细胞防御途径的理解提供一个步骤的改变。在生物技术和人类健康方面也有潜在的应用，特别是利用病毒针对耐药细菌的新方法。

Just like humans, bacteria have a complex immune system to protect them against infection by viruses. The CRISPR system provides adaptive immunity in bacteria, analogous to our antibody system. For the public, CRISPR is often synonymous with the Cas9 enzyme that has allowed rapid advances in genome editing technology. However, Cas9 (a type II CRISPR system) is quite rare in microbes, which more frequently have type I or type III CRISPR systems. Recently, scientists studying type III CRISPR discovered a novel signalling molecule, cyclic oligoadenylate (cOA), that is built from the main energy molecule in the cell, ATP. cOA signals an infected state in cells exposed to a virus, mobilising the cell's defences. We only know about one aspect of this defence - an enzyme that chews up RNA, called Csm6. It seems to buy the cell some time to help clear the infection, but may also cause the cell to "commit suicide" if it can't get rid of the virus. By studying the CRISPR system in different bacteria, we have discovered two new cellular defence enzymes that are activated by the cOA signal to degrade viral genetic material. We have also identified an enzyme made by viruses that rapidly breaks down cOA - it is probably acting as an "anti-CRISPR" to shut down the cell's defences. We want to understand how these three enzymes bind to cOA, how they assume an active shape and what they do, both in vitro (in the test-tube) and in vivo (in the cell). This work will provide a step change in our understanding of an important cell defence pathway. There are also potential applications in biotechnology and human health, in particular for new approaches to target drug resistant bacteria using viruses.