Department of Molecular Microbiology and Immunology, University of Missouri, Columbia, Missouri, USA.
Department of Molecular Microbiology and Immunology, University of Missouri, Columbia, Missouri, USA
J Virol. 2019 May 15;93(11). doi: 10.1128/JVI.02172-18. Print 2019 Jun 1.
Viruses can incorporate foreign glycoproteins to form infectious particles through a process known as pseudotyping. However, not all glycoproteins are compatible with all viruses. Despite the fact that viral pseudotyping is widely used, what makes a virus/glycoprotein pair compatible is poorly understood. To study this, we chose to analyze a gammaretroviral glycoprotein (Env) whose compatibility with different viruses could be modulated through small changes in its cytoplasmic tail (CT). One form of this glycoprotein is compatible with murine leukemia virus (MLV) particles but incompatible with human immunodeficiency virus type 1 (HIV-1) particles, while the second is compatible with HIV-1 particles but not with MLV particles. To decipher the factors affecting virus-specific Env incompatibility, we characterized Env incorporation, maturation, cell-to-cell fusogenicity, and virus-to-cell fusogenicity of each Env. The HIV-1 particle incompatibility correlated with less efficient cleavage of the R peptide by HIV-1 protease. However, the MLV particle incompatibility was more nuanced. MLV incompatibility appeared to be caused by lack of incorporation into particles, yet incorporation could be restored by further truncating the CT or by using a chimeric MLV Gag protein containing the HIV-1 MA without fully restoring infectivity. The MLV particle incompatibility appeared to be caused in part by fusogenic repression in MLV particles through an unknown mechanism. This study demonstrates that the Env CT can dictate functionality of Env within particles in a virus-specific manner. Viruses utilize viral glycoproteins to efficiently enter target cells during infection. How viruses acquire viral glycoproteins has been studied to understand the pathogenesis of viruses and develop safer and more efficient viral vectors for gene therapies. The CTs of viral glycoproteins have been shown to regulate various stages of glycoprotein biogenesis, but a gap still remains in understanding the molecular mechanism of glycoprotein acquisition and functionality regarding the CT. Here, we studied the mechanism of how specific mutations in the CT of a gammaretroviral envelope glycoprotein distinctly affect infectivity of two different viruses. Different mutations caused failure of glycoproteins to function in a virus-specific manner due to distinct fusion defects, suggesting that there are virus-specific characteristics affecting glycoprotein functionality.
病毒可以通过一种称为假型化的过程将外源糖蛋白纳入形成感染性颗粒。然而，并非所有糖蛋白都与所有病毒兼容。尽管病毒假型化被广泛应用，但病毒/糖蛋白对之间的兼容性尚不清楚。为了研究这一点，我们选择分析一种γ逆转录病毒糖蛋白（Env），其与不同病毒的兼容性可以通过其细胞质尾巴（CT）的微小变化来调节。这种糖蛋白的一种形式与鼠白血病病毒（MLV）颗粒兼容，但与人类免疫缺陷病毒 1 型（HIV-1）颗粒不兼容，而另一种形式与 HIV-1 颗粒兼容，但与 MLV 颗粒不兼容。为了解释影响病毒特异性 Env 不兼容性的因素，我们对每种 Env 的 Env 掺入、成熟、细胞间融合性和病毒-细胞融合性进行了表征。HIV-1 颗粒不兼容性与 HIV-1 蛋白酶对 R 肽的切割效率较低有关。然而，MLV 颗粒不兼容性更为复杂。MLV 不兼容性似乎是由于颗粒中缺乏掺入引起的，但通过进一步截断 CT 或使用包含 HIV-1 MA 的嵌合 MLV Gag 蛋白可以恢复掺入，尽管仍未完全恢复感染性。MLV 颗粒不兼容性似乎部分是由于未知机制导致 MLV 颗粒中的融合抑制。本研究表明，Env CT 可以以病毒特异性的方式决定 Env 在颗粒中的功能。病毒在感染过程中利用病毒糖蛋白有效地进入靶细胞。病毒如何获得病毒糖蛋白已被研究用于了解病毒的发病机制，并开发更安全、更有效的基因治疗病毒载体。已经表明病毒糖蛋白的 CT 调节糖蛋白生物发生的各个阶段，但对于 CT 与糖蛋白获得和功能的分子机制仍存在差距。在这里，我们研究了特定突变在 γ逆转录病毒包膜糖蛋白的 CT 中如何以特定方式影响两种不同病毒的感染性的机制。由于不同的融合缺陷，不同的突变导致糖蛋白以病毒特异性的方式无法发挥功能，这表明存在影响糖蛋白功能的病毒特异性特征。
