Husain Matloob, Weisberg Andrea S, Moss Bernard
Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
J Virol. 2007 Mar;81(6):2646-55. doi: 10.1128/JVI.02631-06. Epub 2006 Dec 27.
The primary membrane of vaccinia virus, as well as those of other poxviruses, forms within a discrete cytoplasmic factory region. We recently determined the existence of an operative pathway from the endoplasmic reticulum within the virus factory to nascent viral membranes and demonstrated that a viral protein could be diverted from this pathway to Golgi membranes by the addition of COPII-binding sites (M. Husain, A. S. Weisberg, and B. Moss, Proc. Natl. Acad. Sci. USA, 103:19506-19511, 2006). Here we describe an investigation of the structural features that are required for transit of proteins to the viral membrane. Deletion of either the N-terminal domain or the C-terminal cytoplasmic tail from the conserved A9 protein did not prevent its incorporation into viral membranes, whereas deletion of the transmembrane domain resulted in its distribution throughout the cytoplasm. Nevertheless, replacement of the A9 transmembrane domain with the corresponding region of a nonpoxvirus transmembrane protein or of a vaccinia virus extracellular envelope protein allowed viral membrane targeting, indicating no requirement for a specific amino acid sequence. Remarkably, the epitope-tagged A9 transmembrane domain alone, as well as a heterologous transmembrane domain lacking a poxvirus sequence, was sufficient for viral membrane association. The data are consistent with a sequence-independent pathway in which transmembrane proteins that are synthesized within the virus factory and lack COPII or other binding sites that enable conventional endoplasmic reticulum exiting are incorporated into nascent viral membranes.
痘苗病毒的主要膜以及其他痘病毒的膜，在一个离散的细胞质工厂区域内形成。我们最近确定了一条从病毒工厂内的内质网到新生病毒膜的有效途径，并证明通过添加COPII结合位点，一种病毒蛋白可以从该途径转移到高尔基体膜（M. 侯赛因、A. S. 魏斯伯格和B. 莫斯，《美国国家科学院院刊》，103:19506 - 19511，2006年）。在此，我们描述了对蛋白质转运到病毒膜所需结构特征的研究。从保守的A9蛋白中删除N端结构域或C端细胞质尾巴，并不妨碍其整合到病毒膜中，而删除跨膜结构域则导致其分布在整个细胞质中。然而，用非痘病毒跨膜蛋白或痘苗病毒细胞外包膜蛋白的相应区域替换A9跨膜结构域，可实现病毒膜靶向，这表明不需要特定的氨基酸序列。值得注意的是，单独的表位标记A9跨膜结构域以及缺乏痘病毒序列的异源跨膜结构域，就足以与病毒膜结合。这些数据与一种不依赖序列的途径一致，即在病毒工厂内合成且缺乏COPII或其他能够实现常规内质网出芽的结合位点的跨膜蛋白，会整合到新生病毒膜中。
