Structures of Qβ virions, virus-like particles, and the Qβ-MurA complex reveal internal coat proteins and the mechanism of host lysis
Structures of Qβ virions, virus-like particles, and the Qβ-MurA complex reveal internal coat proteins and the mechanism of host lysis
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DOI：
10.1073/pnas.1707102114
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发表时间：
2017-10-01
影响因子：
11.1
通讯作者：
Zhang, Junjie
中科院分区：
文献类型：
--
作者：
Cui, Zhicheng;Gorzelnik, Karl V.;Zhang, Junjie
在单链RNA噬菌体中，成熟蛋白的一个拷贝与基因组RNA(GRNA)结合，是将噬菌体附着到宿主菌毛上所必需的。对于典型的AlloleviVirus Q beta，成熟蛋白A(2)作为裂解蛋白具有额外的作用，它能够结合和抑制参与肽聚糖生物合成的Mura。在这里，我们使用单粒子冷冻电子显微镜分别在4.7埃、3.3埃和6.1埃分辨率下测定了Qβ病毒粒子、病毒样颗粒和Qβ-穆拉复合体的结构。我们确定A(2)中Beta区的外表面为Mura结合界面。此外，阻止Qβ裂解的Mura突变模式和促进A(2)结合的Mura的构象变化被发现是由于A(2)与底物连接的Mura封闭催化裂解区域之间的紧密匹配。此外，通过比较Qβ病毒粒子和缺乏成熟蛋白的Qβ病毒样颗粒，我们观察到衣壳蛋白中的结构重排，这是将病毒gRNA包装在其主导构象中所必需的。出乎意料的是，我们在病毒粒子的内部发现了一种外壳蛋白二聚体。这种外壳蛋白二聚体与gRNA结合，并与Angstrom的埋藏的β区域相互作用，表明它在衣壳形成的早期阶段被隔离，以促进基因组包装所需的gRNA缩合。这些内化的外壳蛋白是迄今在病毒结构中观察到的最不对称排列的主要衣壳蛋白。
In single-stranded RNA bacteriophages (ssRNA phages) a single copy of the maturation protein binds the genomic RNA(gRNA)and is required for attachment of the phage to the host pilus. For the canonical Allolevivirus Q beta the maturation protein, A(2), has an additional role as the lysis protein, by its ability to bind and inhibit MurA, which is involved in peptidoglycan biosynthesis. Here, we determined structures of Q beta virions, virus-like particles, and the Q beta-MurA complex using single-particle cryoelectron microscopy, at 4.7-angstrom, 3.3-angstrom, and 6.1-angstrom resolutions, respectively. We identified the outer surface of the beta-region in A(2) as the MurA-binding interface. Moreover, the pattern of MurA mutations that block Q beta lysis and the conformational changes of MurA that facilitate A(2) binding were found to be due to the intimate fit between A(2) and the region encompassing the closed catalytic cleft of substrate-liganded MurA. Additionally, by comparing the Q beta virion with Q beta virus-like particles that lack a maturation protein, we observed a structural rearrangement in the capsid coat proteins that is required to package the viral gRNA in its dominant conformation. Unexpectedly, we found a coat protein dimer seques tered in the interior of the virion. This coat protein dimer binds to the gRNA and interacts with the buried beta-region of angstrom suggesting that it is sequestered during the early stage of capsid formation to promote the gRNA condensation required for genome packaging. These inter nalized coat proteins are the most asymmetrically arranged major capsid proteins yet observed in virus structures.