IJkel W F, Westenberg M, Goldbach R W, Blissard G W, Vlak J M, Zuidema D
Laboratory of Virology, Wageningen University and Research Center, Binnenhaven 11, 6709 PD Wageningen, The Netherlands.
Virology. 2000 Sep 15;275(1):30-41. doi: 10.1006/viro.2000.0483.
The entry mechanism of Spodoptera exigua multicapsid nucleopolyhedrovirus (SeMNPV), a group II NPV, in cultured cells was examined. SeMNPV budded virus (BV) enters by endocytosis as do the BVs of the group I NPVs, Autographa californica (Ac) MNPV and Orgyia pseudotsugata (Op) MNPV. In group I NPVs, upon infection acidification of the endosome triggers fusion of the viral and endosomal membrane, which is mediated by the BV envelope glycoprotein GP64. However, the SeMNPV genome lacks a homolog of GP64 envelope fusion protein (EFP). A functional homolog of the OpMNPV GP64 EFP was identified in SeMNPV ORF8 (Se8; 76 kDa) and appeared to be the major BV envelope protein. Surprisingly, a 60-kDa cleavage product of this protein is present in the BV envelope. A furin-like proprotein convertase cleavage site (R-X-K/R-R) was identified immediately upstream of the N-terminus of the mature Se8 protein and this site was also conserved in the Lymantria dispar (Ld) MNPV homolog (Ld130) of Se8. Syncytium formation assays showed that Se8 and Ld130 alone were sufficient to mediate membrane fusion upon acidification of the medium. Furthermore, C-terminal GFP-fusion proteins of Se8 and Ld130 were primarily localized in the plasma membrane of insect cells. This is consistent with their fusogenic activity and supports the conclusion that the Se8 gene product is a functional homolog of the GP64 EFP.
对Ⅱ组核型多角体病毒——甜菜夜蛾多粒包埋核型多角体病毒（SeMNPV）在培养细胞中的进入机制进行了研究。SeMNPV出芽病毒（BV）与Ⅰ组核型多角体病毒苜蓿银纹夜蛾核型多角体病毒（AcMNPV）和云杉毒蛾核型多角体病毒（OpMNPV）的BV一样，通过内吞作用进入细胞。在Ⅰ组核型多角体病毒中，感染后内体的酸化会触发病毒膜与内体膜的融合，这是由BV包膜糖蛋白GP64介导的。然而，SeMNPV基因组缺乏GP64包膜融合蛋白（EFP）的同源物。在SeMNPV的ORF8（Se8；76 kDa）中鉴定出了OpMNPV GP64 EFP的功能同源物，它似乎是主要的BV包膜蛋白。令人惊讶的是，该蛋白的一个60 kDa的裂解产物存在于BV包膜中。在成熟Se8蛋白N端的紧邻上游鉴定出一个类弗林蛋白酶原蛋白转化酶裂解位点（R-X-K/R-R），该位点在Se8的舞毒蛾核型多角体病毒（LdMNPV）同源物（Ld130）中也保守。合胞体形成试验表明，单独的Se8和Ld130足以在培养基酸化时介导膜融合。此外，Se8和Ld130的C端绿色荧光蛋白融合蛋白主要定位于昆虫细胞的质膜。这与它们的融合活性一致，并支持Se8基因产物是GP64 EFP功能同源物的结论。
