The inherent mutational tolerance and antigenic evolvability of influenza hemagglutinin.
The inherent mutational tolerance and antigenic evolvability of influenza hemagglutinin.
复制标题
DOI：
10.7554/elife.03300
复制
发表时间：
2014-07-08
期刊：
影响因子：
7.7
通讯作者：
Bloom JD
中科院分区：
文献类型：
--
作者：
Thyagarajan B;Bloom JD
流感以其逃避针对病毒血凝素的免疫的进化能力而闻名。我们使用深度突变扫描来检查高内在突变耐受性在多大程度上有助于这种抗原进化。我们创造了突变病毒，将≈104氨基酸突变中的大部分整合到A/WSN1933(H1N1)流感的血凝素中。在组织培养中传代这些病毒以筛选功能变异后，我们使用深度测序来量化选择前后的突变频率。这些数据使我们能够推断血凝素中每个部位的每种氨基酸的偏好。这些推论与现有的关于蛋白质结构和功能的知识是一致的，并可以用来创建一个模型，比现有的系统发育模型更好地描述血凝素的进化。我们发现血凝素对抗原部位的突变有很高的内在耐受性，这表明这是导致流感抗原进化的一个因素。DOI：http://dx.doi.org/10.7554/eLife.03300.001流感是对人类健康的主要威胁，很大程度上是因为流感病毒快速进化以逃避免疫系统的识别。这些正在进行的变化也解释了为什么流感疫苗随着时间的推移变得不那么有效，需要每年重新配制。血凝素是流感病毒表面的一种蛋白质，帮助病毒结合和感染宿主细胞。大多数病毒的表面蛋白都是由免疫系统识别的，流感血凝素也不例外。然而，血凝素的不同寻常之处在于，它进化得非常快，以避免被免疫系统识别。这提出了一个重要的问题：流感血凝素蛋白是什么让它如此容易发生变化？Thyagarajan和Bloom通过制作编码血凝素蛋白的基因的突变副本来解决这个问题。有超过10,000种方法可以使蛋白质发生突变，Thyagarajan和Bloom设法实现了绝大多数可能的变化。然后，突变的基因被重新引入病毒中，突变的病毒被允许在细胞中复制几代。Thyagarajan和Bloom对复制的病毒进行了测序--这意味着这些病毒中血凝素蛋白的突变副本仍然有效--并寻找蛋白质中发生变化的位置。那些很少发生变化的区域包括与宿主细胞结合的蛋白质部分，而其他区域--特别是那些被免疫系统识别的区域--更有可能包含突变。Thyagarajan和Bloom接着表明，并不是所有的流感蛋白都具有血凝素改变免疫系统靶标区域的能力，这表明这种能力可能是这种蛋白质的一个独特特征。Thyagarajan和Bloom还提出，这种容忍免疫系统识别的蛋白质部分突变的能力可能对塑造病毒进化以逃避这种识别的能力很重要。现在还需要进一步的工作来观察其他病毒蛋白对突变的耐受性有多强，并揭示一种蛋白质的哪些属性决定了它对突变的耐受性。DOI：http://dx.doi.org/10.7554/eLife.03300.002
Influenza is notable for its evolutionary capacity to escape immunity targeting the viral hemagglutinin. We used deep mutational scanning to examine the extent to which a high inherent mutational tolerance contributes to this antigenic evolvability. We created mutant viruses that incorporate most of the ≈104 amino-acid mutations to hemagglutinin from A/WSN/1933 (H1N1) influenza. After passaging these viruses in tissue culture to select for functional variants, we used deep sequencing to quantify mutation frequencies before and after selection. These data enable us to infer the preference for each amino acid at each site in hemagglutinin. These inferences are consistent with existing knowledge about the protein's structure and function, and can be used to create a model that describes hemagglutinin's evolution far better than existing phylogenetic models. We show that hemagglutinin has a high inherent tolerance for mutations at antigenic sites, suggesting that this is one factor contributing to influenza's antigenic evolution. DOI: http://dx.doi.org/10.7554/eLife.03300.001 Influenza is a major threat to human health largely because the flu virus evolves rapidly to escape recognition by the immune system. These ongoing changes also explain why flu vaccines become less effective over time and need to be reformulated every year. Hemagglutinin is a protein on the surface of the flu virus that helps the virus bind to and infect host cells. The surface proteins of most viruses are recognized by the immune system, and influenza hemagglutinin is no exception. However, hemagglutinin is unusual in that it evolves exceptionally rapidly to avoid being recognized by the immune system. This raises an important question: what is it about the influenza hemagglutinin protein that allows it to change so readily? Thyagarajan and Bloom address this question by making mutant copies of the gene that encodes the hemagglutinin protein. There are over 10,000 ways in which the protein can be mutated, and Thyagarajan and Bloom managed to make the vast majority of the possible changes. The mutated genes were then re-introduced into the virus, and the mutant viruses were allowed to replicate in cells for several generations. Thyagarajan and Bloom sequenced the viruses that had replicated—which meant that the mutant copies of the hemagglutinin protein in these viruses still worked—and looked to see where in the protein the changes had occurred. Those regions that rarely changed included the part of the protein that binds to host cells, whereas other regions—especially those that are recognized by the immune system—were much more likely to contain mutations. Thyagarajan and Bloom then went on to show that not all influenza proteins share hemaglutinin's capacity to change the regions targeted by the immune system, suggesting that this capacity is possibly a unique feature of this protein. Thyagarajan and Bloom also suggest that this capacity to tolerate mutations in parts of proteins that are recognized by the immune system might be important for shaping a virus's ability to evolve to escape this recognition. Future work is now needed to see how tolerant to mutations other viral proteins are, and to reveal which properties of a protein determine its tolerance to mutations. DOI: http://dx.doi.org/10.7554/eLife.03300.002