Schmidt J, Klupp B G, Karger A, Mettenleiter T C
Institute of Molecular and Cellular Virology, Federal Research Centre for Virus Diseases of Animals, Insel Riems, Germany.
J Virol. 1997 Jan;71(1):17-24. doi: 10.1128/JVI.71.1.17-24.1997.
Initial contact between herpesviruses and host cells is mediated by virion envelope glycoproteins which bind to cellular receptors. In several alphaherpesviruses, the nonessential glycoprotein gC has been found to interact with cell surface proteoglycans, whereas the essential glycoprotein gD is involved in stable secondary attachment. In addition, gD is necessary for penetration, which involves fusion between virion envelope and cellular cytoplasmic membrane. As opposed to other alphaherpesvirus gD homologs, pseudorabies virus (PrV) gD is not required for direct viral cell-to-cell spread. Therefore, gD- PrV can be passaged in noncomplementing cells by cocultivating infected and noninfected cells. Whereas infectivity was found to be strictly cell associated in early passages, repeated passaging resulted in the appearance of infectivity in the supernatant, finally reaching titers as high as 10(7) PFU/ml (PrV gD- Pass). Filtration experiments indicated that this infectivity was not due to the presence of infected cells, and the absence of gD was verified by Southern and Western blotting and by virus neutralization. Infection of bovine kidney cells constitutively expressing PrV gD interfered with the infectivity of wild-type PrV but did not inhibit that of PrV gD- Pass. Similar results were obtained after passaging of a second PrV mutant, PrV-376, which in addition to gD also lacks gG, gI, and gE. Penetration assays demonstrated that PrV gD- Pass entered cells much more slowly than wild-type PrV. In summary, our data demonstrate the existence of a gD-independent mode of initiation of infection in PrV and indicate that the essential function(s) that gD performs in wild-type PrV infection can be compensated for after passaging. Therefore, regarding the requirement for gD, PrV seems to be intermediate between herpes simplex virus type 1, in which gD is necessary for penetration and cell-to-cell spread, and varicella-zoster virus (VZV), which lacks a gD gene. Our data show that the relevance of an essential protein can change under selective pressure and thus demonstrate a way in which VZV could have evolved from a PrV-like ancestor.
疱疹病毒与宿主细胞的初始接触是由与细胞受体结合的病毒粒子包膜糖蛋白介导的。在几种α疱疹病毒中，已发现非必需糖蛋白gC与细胞表面蛋白聚糖相互作用，而必需糖蛋白gD参与稳定的二次附着。此外，gD对于病毒穿透是必需的，这涉及病毒粒子包膜与细胞质膜之间的融合。与其他α疱疹病毒gD同源物不同，伪狂犬病病毒（PrV）gD对于病毒直接细胞间传播不是必需的。因此，gD - PrV可以通过共培养感染细胞和未感染细胞在非互补细胞中传代。虽然在早期传代中发现感染性严格与细胞相关，但反复传代导致上清液中出现感染性，最终滴度高达10（7）PFU/ml（PrV gD - Pass）。过滤实验表明这种感染性不是由于存在感染细胞，并且通过Southern和Western印迹以及病毒中和验证了gD的缺失。组成性表达PrV gD的牛肾细胞感染会干扰野生型PrV的感染性，但不抑制PrV gD - Pass的感染性。在第二个PrV突变体PrV - 376传代后也获得了类似结果，该突变体除了gD外还缺乏gG、gI和gE。穿透实验表明PrV gD - Pass进入细胞的速度比野生型PrV慢得多。总之，我们的数据证明了PrV中存在一种不依赖gD的感染起始模式，并表明gD在野生型PrV感染中执行的基本功能在传代后可以得到补偿。因此，就对gD的需求而言，PrV似乎介于1型单纯疱疹病毒（其中gD对于穿透和细胞间传播是必需的）和水痘 - 带状疱疹病毒（VZV，其缺乏gD基因）之间。我们的数据表明，在选择性压力下，一种必需蛋白质的相关性可能会发生变化，从而展示了VZV可能从类似PrV的祖先进化而来的一种方式。
