Determining a molecular pathway for formation of a T=3 capsid using mass spectrometry

病毒仍然是人类、动物和植物的主要病原体。目前最成功的抗病毒疗法依赖于传统的疫苗接种，这是西方在一个多世纪前首次发现的一种技术，不幸的是，这种技术并不适用于许多病毒。更现代的治疗方法是用小分子量化合物、抗病毒药物（如用于治疗艾滋病的药物）来抑制病毒内的特殊酶。不幸的是，这些酶通常与宿主分子共享许多特征，因此大多数抗病毒药物都显示出不必要的副作用。事实上，病毒提供了一个迄今为止尚未被用于治疗的独特分子靶标，即它们的组装途径。简单的病毒只包含一个包裹在蛋白质外壳内的核酸，这些外壳由很少几种不同类型的亚基形成对称的聚集体。整个粒子有一个球形的横截面，看起来有点像足球。在更复杂的含膜病毒中也会形成类似的结构。尽管有关于病毒结构的丰富信息，但还不可能通过实验绘制出任何病毒中从蛋白质亚基到外壳的组装途径。在某种程度上，这是因为传统上研究病毒生命周期的这一方面在技术上是困难的。装配中间体的一个关键特征是它们的分子质量不同。在我们的模型病毒中，一种通常感染实验室细菌的噬菌体，但其结构模仿感染人类的病毒，我们最近发现了如何在试管中减慢组装过程，并使用现代质谱仪测量在通往最终球壳的途径中形成的所有中间产物的质量。这项试验现在使我们能够对组装途径进行最详细的研究，检查噬菌体外壳蛋白和RNA如何参与组装过程，并有希望确定可以揭示新的抗病毒药物靶点的通用原理。

Viruses remain major human, animal and plant pathogens. The most successful current anti-viral therapies rely on traditional vaccination, a technique first identified in the West over a century ago, and unfortunately not simply applicable to many viruses. More modern treatments are directed at inhibiting specialised enzymes within viruses with small molecular weight compounds, anti-viral drugs, such as those used to treat AIDS. Unfortunately, such enzymes usually share many features with host molecules and as a result most anti-viral drugs show unwanted side-effects. In fact viruses offer a unique molecular target that has so far not been exploited therapeutically, namely their assembly pathways. Simple viruses that contain only a nucleic acid enclosed in a protein shell form those shells as symmetrical aggregates from very few different types of subunits. The overall particle has a spherical cross-section and looks somewhat like a soccer ball. Similar structures form within more complex membrane-containing viruses as well. Despite a wealth of information about viral structures it has not yet been possible to map out experimentally an assembly pathway from protein subunit to shell in any virus. In part this is because it has traditionally been technically difficult to study this aspect of viral life-cycles. One key feature of assembly intermediates is their different molecular masses. In our model virus, a bacteriophage that normally infects a laboratory bacterium, but whose architecture mimics that of viruses that infect humans, we have recently discovered how to slow the assembly process in a test tube and measure the masses of all the intermediates formed in the pathwayto the final spherical shell using a modern mass spectrometer. This assay now allows us to take the most detailed look at the assembly pathway, examine how both the phage coat protein and RNA contribute to the assembly process, and hopefully identify generic principles that could reveal novel anti-viral drug targets.