Molecular basis for Rift Valley fever phlebovirus NSs protein function

裂谷热是一种由蚊子传播的病毒引起的危险疾病，在非洲大部分地区和阿拉伯半岛。它造成巨大的经济损失，导致受感染牲畜群的流产率很高（“流产风暴”）。该病毒也经常通过接触受感染的动物或通过蚊子叮咬传播给人类。在大多数情况下，人类疾病的症状与流感或脑膜炎期间所见的症状相似。然而，在大约10%的情况下，严重的疾病发展，包括脑炎（大脑炎症）和出血热（类似于埃博拉病毒），往往是致命的。令人担忧的是，裂谷热也与人类的高堕胎率有关，这增加了另一种广泛传播的病毒对未出生的生命造成严重损害的可能性，让人想起寨卡病毒。动物疫苗可用于预防裂谷热的爆发，但这些疫苗并不完全安全和/或完全有效。没有人类疫苗或治疗方法。裂谷热病毒很有可能在世界上的新地区出现，例如，因为全球变暖有助于能够传播病毒的蚊子从其原始栖息地传播到温带地区。裂谷热是世界卫生组织（WHO）认定的八种急需优先研究的疾病之一，因为它极有可能引起大范围的流行病，而且目前还没有治疗方法或安全的疫苗。裂谷热的疫苗和药物开发需要详细了解该病毒是如何致病的。与其他病毒一样，裂谷热病毒必须抑制受感染动物和人类的免疫反应，才能繁殖和传播。它主要通过使用一种分子，即NS蛋白质来实现这一点。这类似于分子瑞士军刀-蛋白质的不同部分进行许多不同的生物活性。NS的详细工作原理还不清楚，主要是因为到目前为止，蛋白质的三维结构还不清楚。虽然完整的结构仍然缺乏，我们得到了NS的中心部分的结构，这将使我们能够剖析NS的生物功能。NS的一个有趣的特性是在受感染的细胞中形成独特的细长结构（细丝），特别是在储存和访问遗传信息的细胞核中。这些细丝可能对病毒致病很重要。它们破坏了读取遗传信息所需的机制。它们也可能与裂谷热病例中观察到的堕胎有关。我们的分子结构揭示了NSs蛋白如何形成线状组装体，但尚不清楚这些组装体如何在细胞核中形成细丝。我们现在希望利用我们的分子见解和强大的新成像方法，主要是冷冻电子显微镜，在非常高的放大倍数下观察感染细胞中的NSs细丝。这些信息将有助于我们了解国家安全局的瑞士军刀活动。例如，我们将能够看到细胞核中的NS是否与其他分子相互作用。我们还将为NSs蛋白质配备分子手柄，使我们能够将该蛋白质与其结合的其他蛋白质一起分离。同样的分子手柄可以用来使NS在显微镜下发光。这也将使我们能够找出NS如何进入细胞核。我们将使用我们迄今为止获得的知识来设计NS的变体和片段，这将使我们能够获得缺失的结构信息。我们希望解剖NS的结构和功能将有助于我们了解几种危险的病毒是如何引起疾病的，并将为制造破坏NS细丝的药物铺平道路，这些药物可能用于治疗裂谷热。

Rift Valley fever is a dangerous disease caused by a virus that is transmitted by mosquitos in most parts of Africa and the Arabian Peninsula. It causes large economic losses inducing a very high rate of abortions ("abortion storms") in infected livestock herds. The virus is also frequently transmitted to humans through contact with infected animals, or through mosquito bites. In most cases of human disease symptoms are similar to those seen during flu or meningitis. However, in about 10% of cases serious diseases develop, including encephalitis (brain inflammation) and haemorrhagic fever (similar to Ebola) that are often fatal. Worryingly, Rift Valley fever has also been linked to high rates of abortions in humans, raising the possibility of another widespread virus that causes severe damage to unborn life, reminiscent of Zika. Animal vaccines are available for preventing outbreaks of Rift Valley fever, but these are not completely safe and/or fully effective. No human vaccines or treatments are available. Rift Valley fever virus has a high potential to emerge in new regions in the world, for instance because global warming helps mosquitos capable of transmitting the virus spread from their original habitats into temperate zones. Because of its high potential for widespread epidemics, and because no treatments or safe vaccines are available, Rift Vally fever is one of eight diseases that according to the WHO are an urgent research priority.Vaccine and drug development for Rift Valley fever requires a detailed understanding of how the virus causes disease. Like other viruses, Rift Valley fever virus has to suppress the immune response of infected animals and humans in order to multiply and spread. It achieves this mainly by using one molecule, the NSs protein. This operates akin to a molecular Swiss army knife - a number of different biological activities are carried out by different parts of the protein. How NSs works in detail is poorly understood, mainly because up to now the three-dimensional structure of the protein was unknown. While the complete structure is still lacking, we obtained the structure of the central part of NSs, which now will enable us to dissect the biological functions of NSs. One of the intriguing properties of NSs is the formation of distinct elongated structures (filaments) in infected cells, specifically in the cell nucleus where genetic information is stored and accessed. These filaments may be important for the virus to cause disease. They disrupt the machinery required to read out the genetic information. They may also be linked to the abortions observed in Rift Valley fever cases. Our molecular structure revealed how the NSs protein can form thread-like assemblies, but it is unclear how these would come together to form filaments in cell nuclei.We now would like to use our molecular insights and powerful new imaging methods, mainly cryo-electron microscopy, to see at very high magnification what NSs filaments look like in infected cells. This information will help us understand the Swiss army knife activities of NSs. For instance we will be able to see if NSs in cell nuclei interacts with other molecules. We will also equip the NSs protein with molecular handles that will allow us to isolate the protein together with other proteins that it binds to. The same molecular handles can be used to make NSs glow under a microscope. This will also allow us to find out how NSs travels into the cell nucleus. We will use our knowledge gained so far to design variants and fragments of NSs that will allow us to obtain the missing structural information. We expect that dissecting structure and functions of NSs will help us understand how several dangerous viruses cause disease, and will pave the way to making drugs that would disrupt NSs filaments and may be used to treat Rift Valley fever.