Draganova Elizabeth B, Wang Hui, Wu Melanie, Liao Shiqing, Vu Amber, Gonzalez-Del Pino Gonzalo L, Zhou Z Hong, Roller Richard J, Heldwein Ekaterina E
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts, United States of America.
Department of Microbiology, Immunology & Molecular Genetics, University of California, Los Angeles (UCLA), Los Angeles, California, United States of America.
PLoS Pathog. 2024 Jan 16;20(1):e1011936. doi: 10.1371/journal.ppat.1011936. eCollection 2024 Jan.
Nuclear egress is an essential process in herpesvirus replication whereby nascent capsids translocate from the nucleus to the cytoplasm. This initial step of nuclear egress-budding at the inner nuclear membrane-is coordinated by the nuclear egress complex (NEC). Composed of the viral proteins UL31 and UL34, NEC deforms the membrane around the capsid as the latter buds into the perinuclear space. NEC oligomerization into a hexagonal membrane-bound lattice is essential for budding because NEC mutants designed to perturb lattice interfaces reduce its budding ability. Previously, we identified an NEC suppressor mutation capable of restoring budding to a mutant with a weakened hexagonal lattice. Using an established in-vitro budding assay and HSV-1 infected cell experiments, we show that the suppressor mutation can restore budding to a broad range of budding-deficient NEC mutants thereby acting as a universal suppressor. Cryogenic electron tomography of the suppressor NEC mutant lattice revealed a hexagonal lattice reminiscent of wild-type NEC lattice instead of an alternative lattice. Further investigation using x-ray crystallography showed that the suppressor mutation promoted the formation of new contacts between the NEC hexamers that, ostensibly, stabilized the hexagonal lattice. This stabilization strategy is powerful enough to override the otherwise deleterious effects of mutations that destabilize the NEC lattice by different mechanisms, resulting in a functional NEC hexagonal lattice and restoration of membrane budding.
核输出是疱疹病毒复制过程中的一个重要环节,新生衣壳由此从细胞核转运至细胞质。核输出的初始步骤——在内核膜上出芽——由核输出复合体(NEC)协调。NEC由病毒蛋白UL31和UL34组成,当衣壳芽生进入核周空间时,NEC使衣壳周围的膜变形。NEC寡聚形成六边形膜结合晶格对于出芽至关重要,因为设计用于扰乱晶格界面的NEC突变体降低了其出芽能力。此前,我们鉴定出一种NEC抑制突变,能够使具有弱化六边形晶格的突变体恢复出芽。通过使用既定的体外出芽试验和单纯疱疹病毒1型感染细胞实验,我们表明该抑制突变可使多种出芽缺陷型NEC突变体恢复出芽,从而起到通用抑制剂的作用。抑制性NEC突变体晶格的低温电子断层扫描显示出一种类似于野生型NEC晶格的六边形晶格,而非其他晶格。使用X射线晶体学的进一步研究表明,抑制突变促进了NEC六聚体之间新接触的形成,表面上稳定了六边形晶格。这种稳定策略强大到足以克服通过不同机制使NEC晶格不稳定的突变的有害影响,从而形成功能性的NEC六边形晶格并恢复膜出芽。