Sadanandan Sajna Anand, Ekström Jens-Ola, Jonna Venkateswara Rao, Hofer Anders, Hultmark Dan
Department of Molecular Biology, Umeå University, SE-901 87 Umeå, Sweden.
Department of Molecular Biology, Umeå University, SE-901 87 Umeå, Sweden; Institute of Biomedical Technology, University of Tampere, FI-33520 Tampere, Finland.
Virus Res. 2016 Sep 2;223:20-7. doi: 10.1016/j.virusres.2016.06.011. Epub 2016 Jun 18.
Nora virus is an enteric virus that causes persistent, non-pathological infection in Drosophila melanogaster. It replicates in the fly gut and is transmitted via the fecal-oral route. Nora virus has a single-stranded positive-sense RNA genome, which is translated in four open reading frames. Reading frame three encodes the VP3 protein, the structure and function of which we have investigated in this work. We have shown that VP3 is a trimer that has an α-helical secondary structure, with a functionally important coiled-coil domain. In order to identify the role of VP3 in the Nora virus life cycle, we constructed VP3-mutants using the cDNA clone of the virus. Our results show that VP3 does not have a role in the actual assembly of the virus particles, but virions that lack VP3 or harbor VP3 with a disrupted coiled coil domain are incapable of transmission via the fecal-oral route. Removing the region downstream of the putative coiled coil appears to have an effect on the fitness of the virus but does not hamper its replication or transmission. We also found that the VP3 protein and particularly the coiled coil domain are crucial for the stability of Nora virus virions when exposed to heat or proteases. Hence, we propose that VP3 is imperative to Nora virus virions as it confers stability to the viral capsid.
诺拉病毒是一种肠道病毒，可在黑腹果蝇中引起持续性的非致病性感染。它在果蝇肠道中复制，并通过粪口途径传播。诺拉病毒具有单链正义RNA基因组，该基因组在四个开放阅读框中进行翻译。阅读框三编码VP3蛋白，我们在这项工作中对其结构和功能进行了研究。我们已经表明，VP3是一种三聚体，具有α-螺旋二级结构，带有一个功能重要的卷曲螺旋结构域。为了确定VP3在诺拉病毒生命周期中的作用，我们使用该病毒的cDNA克隆构建了VP3突变体。我们的结果表明，VP3在病毒颗粒的实际组装中不起作用，但缺乏VP3或带有破坏的卷曲螺旋结构域的VP3的病毒粒子无法通过粪口途径传播。去除假定的卷曲螺旋下游区域似乎对病毒的适应性有影响，但不影响其复制或传播。我们还发现，VP3蛋白，特别是卷曲螺旋结构域，在诺拉病毒粒子暴露于热或蛋白酶时对其稳定性至关重要。因此，我们提出VP3对诺拉病毒粒子至关重要，因为它赋予病毒衣壳稳定性。
