Structural and Computational Biology Unit, European Molecular Biology Laboratory, Heidelberg, Germany.
PLoS Pathog. 2010 Nov 24;6(11):e1001215. doi: 10.1371/journal.ppat.1001215.
HIV-1 buds form infected cells in an immature, non-infectious form. Maturation into an infectious virion requires proteolytic cleavage of the Gag polyprotein at five positions, leading to a dramatic change in virus morphology. Immature virions contain an incomplete spherical shell where Gag is arranged with the N-terminal MA domain adjacent to the membrane, the CA domain adopting a hexameric lattice below the membrane, and beneath this, the NC domain and viral RNA forming a disordered layer. After maturation, NC and RNA are condensed within the particle surrounded by a conical CA core. Little is known about the sequence of structural changes that take place during maturation, however. Here we have used cryo-electron tomography and subtomogram averaging to resolve the structure of the Gag lattice in a panel of viruses containing point mutations abolishing cleavage at individual or multiple Gag cleavage sites. These studies describe the structural intermediates correlating with the ordered processing events that occur during the HIV-1 maturation process. After the first cleavage between SP1 and NC, the condensed NC-RNA may retain a link to the remaining Gag lattice. Initiation of disassembly of the immature Gag lattice requires cleavage to occur on both sides of CA-SP1, while assembly of the mature core also requires cleavage of SP1 from CA.
HIV-1 芽从感染细胞中以不成熟、无感染性的形式形成。成熟为有感染性的病毒粒子需要在五个位置对 Gag 多蛋白进行蛋白水解切割，导致病毒形态发生显著变化。不成熟的病毒粒子包含一个不完整的球形外壳，其中 Gag 排列在 N 端 MA 结构域与膜相邻，CA 结构域在膜下形成六聚体晶格，在这之下，NC 结构域和病毒 RNA 形成无序层。成熟后，NC 和 RNA 在由锥形 CA 核心包围的颗粒内浓缩。然而，关于成熟过程中发生的结构变化的顺序知之甚少。在这里，我们使用冷冻电子断层扫描和子断层平均化来解析一组包含点突变的病毒中的 Gag 晶格结构，这些突变会在单个或多个 Gag 切割位点处阻止切割。这些研究描述了与 HIV-1 成熟过程中发生的有序加工事件相关的结构中间体。在 SP1 和 NC 之间的第一次切割之后，浓缩的 NC-RNA 可能与剩余的 Gag 晶格保持联系。不成熟的 Gag 晶格解体的开始需要在 CA-SP1 的两侧发生切割，而成熟核心的组装也需要从 CA 上切割 SP1。
