Departments of Pathology, Microbiology and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
mBio. 2012 Feb 7;3(1). doi: 10.1128/mBio.00270-11. Print 2012.
Respiratory syncytial virus (RSV) is a single-stranded RNA virus in the Paramyxoviridae family that assembles into filamentous structures at the apical surface of polarized epithelial cells. These filaments contain viral genomic RNA and structural proteins, including the fusion (F) protein, matrix (M) protein, nucleoprotein (N), and phosphoprotein (P), while excluding F-actin. It is known that the F protein cytoplasmic tail (FCT) is necessary for filament formation, but the mechanism by which the FCT mediates assembly into filaments is not clear. We hypothesized that the FCT is necessary for interactions with other viral proteins in order to form filaments. In order to test this idea, we expressed the F protein with cytoplasmic tail (CT) truncations or specific point mutations and determined the abilities of these variant F proteins to form filaments independent of viral infection when coexpressed with M, N, and P. Deletion of the terminal three FCT residues (amino acids Phe-Ser-Asn) or mutation of the Phe residue resulted in a loss of filament formation but did not affect F-protein expression or trafficking to the cell surface. Filament formation could be restored by addition of residues Phe-Ser-Asn to an FCT deletion mutant and was unaffected by mutations to Ser or Asn residues. Second, deletion of residues Phe-Ser-Asn or mutation of the Phe residue resulted in a loss of M, N, and P incorporation into virus-like particles. These data suggest that a C-terminal Phe residue in the FCT mediates assembly through incorporation of internal virion proteins into virus filaments at the cell surface.
Respiratory syncytial virus (RSV) is a leading cause of bronchiolitis and pneumonia in infants and the elderly worldwide. There is no licensed RSV vaccine and only limited therapeutics for use in infected patients. Many aspects of the RSV life cycle have been studied, but the mechanisms that drive RSV assembly at the cell surface are not well understood. This study provides evidence that a specific residue in the RSV fusion protein cytoplasmic tail coordinates assembly into viral filaments by mediating the incorporation of internal virion proteins. Understanding the mechanisms that drive RSV assembly could lead to targeted development of novel antiviral drugs. Moreover, since RSV exits infected cells in an ESCRT (endosomal sorting complexes required for transport)-independent manner, these studies may contribute new knowledge about a general strategy by which ESCRT-independent viruses mediate outward bud formation using viral protein-mediated mechanisms during assembly and budding.
呼吸道合胞病毒（RSV）是导致全球婴儿和老年人细支气管炎和肺炎的主要原因。目前尚无 RSV 疫苗获批，且仅有有限的治疗药物可用于感染患者。RSV 生命周期的许多方面都已经得到了研究，但 RSV 在细胞表面组装的机制仍不清楚。本研究提供了证据表明，RSV 融合蛋白胞质尾中的特定残基通过介导内部病毒蛋白掺入病毒丝状结构来协调组装。了解推动 RSV 组装的机制可能会导致针对新型抗病毒药物的靶向开发。此外，由于 RSV 以非 ESCRT（内体分选复合物必需的运输）依赖的方式从感染细胞中释放，因此这些研究可能为非 ESCRT 依赖型病毒在组装和出芽过程中利用病毒蛋白介导的机制介导外向芽形成提供了关于一般策略的新知识。
