RNA and Nucleocapsid Are Dispensable for Mature HIV-1 Capsid Assembly
RNA and Nucleocapsid Are Dispensable for Mature HIV-1 Capsid Assembly
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RNA 和核衣壳对于成熟的 HIV-1 衣壳组装来说是可有可无的
DOI：
10.1128/jvi.00750-15
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发表时间：
2015
影响因子：
5.4
通讯作者：
Müller
中科院分区：
文献类型：
--
作者：
Mattei;Flemming;Anders-Össwein;Kräusslich;Briggs;Müller
人类免疫缺陷病毒1型(HIV-1)是以一种未成熟的、非传染性的形式从感染细胞中释放出来的，其中结构多蛋白Gag排列在六面体晶格中，形成一个不完整的球形外壳。病毒的成熟是由病毒蛋白酶介导的，它在五个位置裂解Gag，释放CA(衣壳)蛋白，CA(衣壳)蛋白形成包裹浓缩RNA基因组的圆锥形衣壳。这种结构重排的途径目前还不清楚，也不清楚锥体组装是如何启动的。RNA是逆转录病毒不可或缺的结构成分，病毒核蛋白核心被认为是对成熟衣壳组装的核化。我们通过在病毒环境中将HIV-1 Gag的RNA结合NC(核衣壳)结构域和邻近的间隔肽2(SP2)替换为亮氨酸拉链(LZ)蛋白-蛋白质相互作用结构域[Gag(LZ)]来解决这一假设。我们发现携带Gag(LZ)的病毒[HIV(LZ)]被有效地释放，病毒多蛋白被蛋白质水解性加工，尽管效率降低。冷冻电子断层扫描显示，这些颗粒缺乏浓缩的核蛋白，并含有更多比例的异常核心形态，要么是由于缺乏RNA，要么是由于改变了GAG的加工过程。然而，相当大比例的HIV(LZ)颗粒含有具有野生型形态的成熟衣壳。这些结果清楚地表明，核蛋白复合体对于病毒环境中成熟的HIV-1衣壳组装来说是必不可少的。重要的是，包裹在病毒RNA基因组上的封闭的圆锥形衣壳的形成对于HIV-1的感染性是必不可少的。目前尚不清楚是什么病毒成分在病毒形态发生过程中启动和调节衣壳的形成，但已提出核糖核蛋白复合体起作用。为了验证这一点，我们制备了缺乏病毒核衣壳蛋白和RNA的病毒样颗粒，并用冷冻电子断层扫描分析了它们的三维结构。虽然大多数病毒粒子在这些条件下表现出异常的形态，但也有一些粒子表现出正常的成熟形态，并有闭合的锥形衣壳。这些数据表明，RNA和核衣壳蛋白的存在不是形成成熟的锥形HIV-1衣壳所必需的。
Human immunodeficiency virus type 1 (HIV-1) is released from infected cells in an immature, noninfectious form in which the structural polyprotein Gag is arranged in a hexameric lattice, forming an incomplete spherical shell. Maturation to the infectious form is mediated by the viral protease, which cleaves Gag at five sites, releasing the CA (capsid) protein, which forms a conical capsid encasing the condensed RNA genome. The pathway of this structural rearrangement is currently not understood, and it is unclear how cone assembly is initiated. RNA represents an integral structural component of retroviruses, and the viral nucleoprotein core has previously been proposed to nucleate mature capsid assembly. We addressed this hypothesis by replacing the RNA-binding NC (nucleocapsid) domain of HIV-1 Gag and the adjacent spacer peptide 2 (SP2) by a leucine zipper (LZ) protein-protein interaction domain [Gag(LZ)] in the viral context. We found that Gag(LZ)-carrying virus [HIV(LZ)] was efficiently released and viral polyproteins were proteolytically processed, though with reduced efficiency. Cryo-electron tomography revealed that the particles lacked a condensed nucleoprotein and contained an increased proportion of aberrant core morphologies caused either by the absence of RNA or by altered Gag processing. Nevertheless, a significant proportion of HIV(LZ) particles contained mature capsids with the wild-type morphology. These results clearly demonstrate that the nucleoprotein complex is dispensable as a nucleator for mature HIV-1 capsid assembly in the viral context.IMPORTANCEFormation of a closed conical capsid encasing the viral RNA genome is essential for HIV-1 infectivity. It is currently unclear what viral components initiate and regulate the formation of the capsid during virus morphogenesis, but it has been proposed that the ribonucleoprotein complex plays a role. To test this, we prepared virus-like particles lacking the viral nucleocapsid protein and RNA and analyzed their three-dimensional structure by cryo-electron tomography. While most virions displayed an abnormal morphology under these conditions, some particles showed a normal mature morphology with closed conical capsids. These data demonstrate that the presence of RNA and the nucleocapsid protein is not required for the formation of a mature, cone-shaped HIV-1 capsid.
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