Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, China.
Virol J. 2013 Dec 16;10:354. doi: 10.1186/1743-422X-10-354.
Viral envelope proteins are always proposed to exert important function during virus infection and replication. Vertebrate iridoviruses are enveloped large DNA virus, which can cause great economic losses in aquaculture and ecological destruction. Although numerous iridovirus envelope proteins have been identified using bioinformatics and proteomic methods, their roles in virus infection remained largely unknown.
Using SMART and TMHMM programs, we investigated the structural characteristics of Singapore grouper iridovirus (SGIV) VP19. A specific antibody against VP19 was generated and the expression profile of VP19 was clarified. The subcellular localization of VP19 in the absence or presence of other viral products was determined via transfection and immune fluorescence assay. In addition, Western blot assay and electron microscopy examination were performed to demonstrate whether SGIV VP19 was an envelope protein or a capsid protein.
Here, SGIV VP19 was cloned and characterized. Among all sequenced iridoviruses, VP19 and its orthologues shared common features, including 19 invariant cysteines, a proline-rich motif and a predicted transmembrane domain. Subsequently, the protein synthesis of VP19 was only detected at the late stage of SGIV infection and inhibited obviously by treating with AraC, confirming that VP19 was a late expressed protein. Ectopic expression of EGFP-VP19 in vitro displayed a punctate pattern in the cytoplasm. In SGIV infected cells, the newly synthesized VP19 protein was initially localized in the cytoplasm in a punctate pattern, and then aggregated into the virus assembly site at the late stage of SGIV infection, suggesting that other viral protein products were essential for VP19's function during SGIV infection. In addition, Western blot assay and electron microscopy observation revealed that SGIV VP19 was associated with viral envelope, which was different from major capsid protein (MCP).
Taken together, the current data suggested that VP19 represented a conserved envelope protein in iridovirus, and might contribute greatly to virus assembly during virus infection.
病毒包膜蛋白在病毒感染和复制过程中总是被认为发挥着重要作用。脊椎动物虹彩病毒是有包膜的大型 DNA 病毒，可在水产养殖和生态破坏方面造成巨大的经济损失。尽管已经使用生物信息学和蛋白质组学方法鉴定了许多虹彩病毒包膜蛋白，但它们在病毒感染中的作用在很大程度上仍是未知的。
使用 SMART 和 TMHMM 程序，我们研究了新加坡石斑鱼虹彩病毒（SGIV）VP19 的结构特征。生成了针对 VP19 的特异性抗体，并阐明了 VP19 的表达谱。通过转染和免疫荧光测定，确定了 VP19 在不存在或存在其他病毒产物时的亚细胞定位。此外，进行 Western blot 分析和电子显微镜检查，以证明 SGIV VP19 是包膜蛋白还是衣壳蛋白。
在这里，克隆并鉴定了 SGIV VP19。在所有测序的虹彩病毒中，VP19 和其同源物具有共同的特征，包括 19 个不变的半胱氨酸、富含脯氨酸的基序和预测的跨膜结构域。随后，只有在 SGIV 感染的晚期才能检测到 VP19 的蛋白质合成，并且用 AraC 处理明显抑制了 VP19 的蛋白质合成，这证实了 VP19 是一种晚期表达的蛋白质。体外表达 EGFP-VP19 呈现出细胞质中的点状模式。在 SGIV 感染的细胞中，新合成的 VP19 蛋白最初在细胞质中呈点状，然后在 SGIV 感染的晚期聚集到病毒组装部位，这表明其他病毒蛋白产物对于 VP19 在 SGIV 感染期间的功能是必需的。此外，Western blot 分析和电子显微镜观察表明，SGIV VP19 与病毒包膜相关，这与主要衣壳蛋白（MCP）不同。
综上所述，目前的数据表明，VP19 是虹彩病毒中保守的包膜蛋白，可能在病毒感染过程中对病毒组装有很大贡献。
