PDF(Pubmed)
Abstract：
Bombyx mori nucleopolyhedrovirus (BmNPV) is the primary pathogen of silkworms that causes severe economic losses in sericulture. GP64 is the key membrane fusion protein that mediates budded virus (BV) fusion with the host cell membrane. Previously, we found that the n-region of the GP64 signal peptide (SP) is required for protein secretion and viral pathogenicity; however, our understanding of BmNPV GP64 remains limited. Here, we first reported that BmNPV GP64 retained its SP in the mature protein and virion in only host cells but did not retain in nonhost cells. Uncleaved SP mediates protein targeting to the cytomembrane or secretion in Bombyx mori cells. The exitance of the n-region extended the transmembrane helix length, which resulted in the cleavage site to be located in the helix structure and thus blocked cleavage from signal peptidase (SPase). Without the n-region, the protein fails to be transported to the cytomembrane, but this failure can be rescued by the cleavage site mutation of SP. Helix-breaking mutations in SP abolished protein targeting to the cytomembrane and secretion. Our results revealed a previously unrecognized mechanism by which SP of membrane fusion not only determines protein localization but also determines viral pathogenicity, which highlights the escape mechanism of SP from the cleavage by SPase. IMPORTANCE BmNPV is the primary pathogen of silkworms, which causes severe economic losses in sericulture. BmNPV and Autographa californica multiple nucleopolyhedrovirus (AcMNPV) are closely related group I alphabaculoviruses, but they exhibit nonoverlapping host specificity. Recent studies suppose that GP64 is a determinant of host range, while knowledge remains limited. In this study, we revealed that BmNPV GP64 retained its SP in host cells but not in nonhost cells, and the SP retention is required for GP64 secretion across the cytomembrane. This is the first report that a type I membrane fusion protein retained its SP in mature proteins and virions. Our results unveil the mechanism by which SP GP64 escapes cleavage and the role of SP in protein targeting. This study will help elucidate an important mechanistic understanding of BmNPV infection and host range specificity.
摘要：
家蚕核型多角体病毒（BmNPV）是家蚕的主要病原体，在养蚕中造成严重的经济损失。GP64是介导出芽病毒(BV)与宿主细胞膜融合的关键膜融合蛋白。以前,我们发现GP64信号肽（SP）的n区是蛋白质分泌和病毒致病性所必需的；然而，我们对BmNPVGP64的理解仍然有限。这里,我们首次报道BmNPVGP64在成熟蛋白和病毒体中保留其SP仅在宿主细胞中，但在非宿主细胞中不保留。未裂解的SP介导蛋白质靶向细胞膜或在家蚕细胞中分泌。n区的存在延长了跨膜螺旋的长度，这导致切割位点位于螺旋结构中，从而阻断了信号肽酶（SPase）的切割。没有n区，蛋白质不能被运输到细胞膜,但是这种失败可以通过SP的切割位点突变来挽救。SP中的螺旋断裂突变消除了蛋白质靶向细胞膜和分泌。我们的结果揭示了一种以前未被认识的机制，通过这种机制，膜融合的SP不仅决定了蛋白质的定位，而且决定了病毒的致病性。这突出了SP从SPase裂解中的逃逸机制。重要性BmNPV是蚕的主要病原体，给蚕业造成了严重的经济损失。BmNPV和加利福尼亚Autographa多核多角体病毒（AcMNPV）是密切相关的I组字母杆状病毒，但它们表现出不重叠的宿主特异性。最近的研究假设GP64是宿主范围的决定因素，而知识仍然有限。在这项研究中,我们发现BmNPVGP64在宿主细胞中保留了其SP，而在非宿主细胞中没有保留，并且SP保留是GP64跨细胞膜分泌所必需的。这是I型膜融合蛋白在成熟蛋白和病毒体中保留其SP的首次报道。我们的结果揭示了SPGP64逃避裂解的机制以及SP在蛋白质靶向中的作用。这项研究将有助于阐明对BmNPV感染和宿主范围特异性的重要机制理解。
