Importin-5 functions as a chaperone for viral glycoproteins to promote virus budding.

Thousands of people are affected by arenavirus infections annually and no specific and safe antiviral therapy for arenaviruses are available. Thus, there is an urgent need to develop effective vaccines or therapeutic strategies to combat arenavirus infections. This task is hampered owing to limited understanding of the molecular details of virus-host interactions. Here, we performed affinity tag-purification mass spectrometry to generate a protein-protein interaction (PPI) map between host cells and arenavirus lymphocytic choriomeningitis virus (LCMV) proteins. We uncovered 299 high-confidence LCMV-host PPIs, including one between the LCMV glycoprotein and host karyopherin importin-5 (IPO5). We further showed that the C-terminus cytosol tail of the viral glycoprotein enriched in basic amino acids, directly interacts with IPO5. IPO5 acts as a chaperone to facilitate the transport and translocation of glycoproteins to the host cell membrane surface, thereby promoting viral budding. On this basis, a highly attenuated LCMV mutant (LCMV-EED) was generated, which protected mice from the lethal challenge of LCMV. Notably, we found that several enveloped RNA viruses also possess similar C-termini cytosol tails that contain basic amino acids of glycoproteins, which plays an important role in the effect of IPO5 on viral budding. Thus, the C-terminus of glycoproteins can serve as a novel broad-spectrum target for the development of vaccines and antivirals.

每年有数以千计的人群受到沙粒病毒（arenavirus）感染，且目前尚无针对沙粒病毒的特异性安全抗病毒治疗方案。因此，亟需开发有效的疫苗或治疗策略以对抗沙粒病毒感染。由于对病毒-宿主相互作用的分子细节认知有限，相关研发进程受到掣肘。本研究通过亲和标签纯化质谱（affinity tag-purification mass spectrometry）技术，构建了宿主细胞与沙粒病毒淋巴细胞性脉络丛脑膜炎病毒（lymphocytic choriomeningitis virus, LCMV）蛋白之间的蛋白质相互作用（protein-protein interaction, PPI）图谱。我们共鉴定得到299组高置信度LCMV-宿主PPI，其中包含LCMV糖蛋白（glycoprotein）与宿主核转运蛋白importin-5（IPO5）之间的相互作用。进一步研究证实，病毒糖蛋白中富含碱性氨基酸的C端胞质尾可直接与IPO5结合。IPO5作为分子伴侣（chaperone），可促进糖蛋白向宿主细胞膜表面的转运与易位，进而推动病毒出芽（viral budding）。基于上述发现，我们构建了一株高度减毒的LCMV突变株（attenuated LCMV mutant, LCMV-EED），该突变株可使小鼠免受LCMV致死性感染攻击。值得注意的是，我们发现多种有包膜RNA病毒（enveloped RNA virus）的糖蛋白同样拥有类似的富含碱性氨基酸的C端胞质尾，且该结构在IPO5介导的病毒出芽过程中发挥关键作用。综上，糖蛋白C端可作为开发疫苗与抗病毒药物的新型广谱靶点（broad-spectrum target）。