Promiscuous interactions and protein disaggregases determine the material state of stress-inducible RNP granules.
Promiscuous interactions and protein disaggregases determine the material state of stress-inducible RNP granules.
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DOI：
10.7554/elife.06807
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发表时间：
2015-08-04
期刊：
影响因子：
7.7
通讯作者：
Alberti S
中科院分区：
文献类型：
--
作者：
Kroschwald S;Maharana S;Mateju D;Malinovska L;Nüske E;Poser I;Richter D;Alberti S
RNA-蛋白质(RNP)颗粒被认为是通过形成固体RNA/蛋白质聚集体或通过相分离形成液体RNA/蛋白质相来组装的。哪种模型描述活细胞中的RNP颗粒仍不清楚。在这项研究中，我们分析了发芽酵母中的P小体，发现它们具有类似液体的性质。令人惊讶的是，酵母应激颗粒采用了一种不同的物质状态，这让人想起固体蛋白质聚集体，并由蛋白质解聚酶控制。通过使用异位成核RNP颗粒的实验，我们进一步证明RNP颗粒的形成不依赖于淀粉样聚集，而是涉及许多混杂的相互作用。最后，我们证明了应激颗粒在哺乳动物细胞中具有不同的性质，在那里它们表现出类似液体的行为。因此，我们认为RNP颗粒的物质状态是灵活的，而酵母应激颗粒的固态是对极端环境的一种适应，这是由于强大的解聚机的存在。DOI：http://dx.doi.org/10.7554/eLife.06807.001基因由编码蛋白质的长dna组成。DNA首先被“转录”成RNA分子，然后再被翻译成蛋白质。在大多数细胞中，RNA分子存在于一种称为核糖核蛋白(RNP)颗粒的结构中。它们包含运输、储存和分解RNA所需的蛋白质机制。P小体和应激颗粒是两种类型的RNP颗粒，存在于从酵母到人类的所有细胞中。P小体一直存在，而当细胞经历压力条件时，如缺乏营养或高温，压力颗粒就会聚集在一起。一旦压力被克服，压力颗粒就会被分解。RNP颗粒如何在细胞中组装的确切细节仍然知之甚少。有一种理论认为，RNP颗粒是通过一种称为“相分离”的物理过程形成的，在这种过程中，超过一定临界浓度的RNA分子和蛋白质凝聚成液滴。其他研究表明，当所谓的普恩样蛋白自发聚集在一起并开始聚集形成纤维时，RNP颗粒就会出现。这些颗粒的行为更像固体而不是液体。Kroschwald等人。现在，他们使用一种可以区分类液体和类固体结构的化合物，分析了酵母和人类细胞中P小体和压力颗粒的形成。结果表明，P小体和应激颗粒在酵母细胞中的表现截然不同。虽然P小体确实是液滴，但应激颗粒本质上更固体，其作用类似于蛋白质聚集体。那么，为什么两者之间会有区别呢？以前的工作已经知道，当细胞受到压力时，许多蛋白质会错误折叠并开始聚集。Kroschwald等人。研究发现，应力颗粒的形成与集合体的形成相吻合，说明应力颗粒本身就是一种集合体。此外，应激颗粒的形成似乎并不涉及类Pron纤维，而是类Pron蛋白可以很容易地以混杂的方式与其他蛋白质相互作用，从而促进应激颗粒的播种和生长。Kroschwald等人。接下来研究了人类细胞，观察到在这些细胞中，P小体和应激颗粒都是液滴。这些结果共同表明，组装P小体和应力颗粒的物理性质和方法可能因生物不同而不同。未来的工作将调查，当酵母细胞受到压力时，形成固体而不是液体压力颗粒的能力是否为酵母细胞提供了额外的保护。此外，应激颗粒是否以及如何转化为神经退行性疾病中常见的病理性RNP聚集体还有待测试。DOI：http://dx.doi.org/10.7554/eLife.06807.002
RNA-protein (RNP) granules have been proposed to assemble by forming solid RNA/protein aggregates or through phase separation into a liquid RNA/protein phase. Which model describes RNP granules in living cells is still unclear. In this study, we analyze P bodies in budding yeast and find that they have liquid-like properties. Surprisingly, yeast stress granules adopt a different material state, which is reminiscent of solid protein aggregates and controlled by protein disaggregases. By using an assay to ectopically nucleate RNP granules, we further establish that RNP granule formation does not depend on amyloid-like aggregation but rather involves many promiscuous interactions. Finally, we show that stress granules have different properties in mammalian cells, where they show liquid-like behavior. Thus, we propose that the material state of RNP granules is flexible and that the solid state of yeast stress granules is an adaptation to extreme environments, made possible by the presence of a powerful disaggregation machine. DOI: http://dx.doi.org/10.7554/eLife.06807.001 Genes consist of long stretches of DNA that code for proteins. The DNA is first ‘transcribed’ to produce an RNA molecule, which is then translated into a protein. In most cells, RNA molecules are present within a structure called ribonucleoprotein (RNP for short) granules. These contain the protein machinery needed to transport, store, and break down RNAs. P bodies and stress granules are two types of RNP granules found in all cells, from yeast to human. P bodies are present at all times, whereas stress granules assemble when a cell experiences stressful conditions, such as a lack of nutrients or high temperatures. Once the stress has been overcome, the stress granules are disassembled. The precise details of how RNP granules assemble in cells remain poorly understood. One theory suggests that RNP granules form through a physical process called ‘phase separation’ in which RNA molecules and proteins above a certain critical concentration condense to form a liquid droplet. Other research has suggested that RNP granules arise when so-called prion-like proteins spontaneously clump together and start aggregating to form fibers. These granules would behave more like solids than liquids. Kroschwald et al. have now analyzed how P bodies and stress granules form in yeast and human cells using a chemical compound that can distinguish between liquid-like and solid-like structures. The results revealed that P bodies and stress granules behave very differently in yeast cells. While P bodies are indeed liquid droplets, stress granules are more solid in nature and act like protein aggregates. So why is there a difference between the two? It is known from previous work that when cells are stressed, many proteins misfold and start aggregating. Kroschwald et al. found that the formation of stress granules coincides with the formation of aggregates, suggesting that stress granules themselves are a type of aggregate. Furthermore, stress granule formation does not seem to involve prion-like fibers, but rather prion-like proteins can easily interact with other proteins in a promiscuous way, thus promoting the seeding of stress granules and their growth. Kroschwald et al. next studied human cells and observed that in these cells, both P bodies and stress granules were liquid droplets. These results together suggest that the physical properties and method of assembling P bodies and stress granules can vary from one organism to another. Future work will investigate whether the ability to form solid rather than liquid stress granules provides extra protection to yeast cells when they are stressed. It also remains to be tested whether and how stress granules convert into the pathological RNP aggregates that are often seen in neurodegenerative diseases. DOI: http://dx.doi.org/10.7554/eLife.06807.002