Jiangsu Key Laboratory of Sericultural Biology and Biotechnology, School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang, Jiangsu, People's Republic of China.
Key Laboratory of Genetic Improvement of Sericulture in the Ministry of Agriculture, Sericultural Research Institute, Chinese Academy of Agricultural Science, Zhenjiang, Jiangsu, People's Republic of China.
Microbiol Spectr. 2022 Aug 31;10(4):e0191322. doi: 10.1128/spectrum.01913-22. Epub 2022 Aug 8.
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. 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.
家蚕核型多角体病毒（BmNPV）是引起蚕业严重经济损失的主要病原体。GP64 是介导芽生病毒（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 区对于蛋白分泌和病毒致病性是必需的；然而，我们对 BmNPV GP64 的了解仍然有限。在这里，我们首次报道，BmNPV GP64 在仅在宿主细胞中保留其在成熟蛋白和病毒粒子中的 SP，但不在非宿主细胞中保留。未切割的 SP 介导蛋白靶向细胞质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，导致切割位点位于螺旋结构中，从而阻止了信号肽酶（SPase）的切割。没有 n 区，蛋白质就无法转运到细胞质膜，但 SP 切割位点的突变可以挽救这种失败。SP 中的螺旋断裂突变阻止了蛋白靶向细胞质膜和分泌。我们的结果揭示了一个以前未被认识的机制，即膜融合的 SP 不仅决定蛋白定位，而且决定病毒的致病性，这突出了 SP 逃避 SPase 切割的逃逸机制。BmNPV 是家蚕的主要病原体，在蚕业中造成严重的经济损失。BmNPV 和美洲棉铃虫多角体病毒（AcMNPV）是密切相关的 I 组α杆状病毒，但它们表现出非重叠的宿主特异性。最近的研究假设 GP64 是宿主范围的决定因素，但知识仍然有限。在这项研究中，我们揭示了 BmNPV GP64 在宿主细胞中保留其 SP，但在非宿主细胞中不保留，并且 SP 的保留是 GP64 穿过细胞质膜分泌所必需的。这是第一个报道 I 型膜融合蛋白在成熟蛋白和病毒粒子中保留其 SP 的报告。我们的结果揭示了 SP GP64 逃避切割的机制以及 SP 在蛋白靶向中的作用。这项研究将有助于阐明 BmNPV 感染和宿主范围特异性的重要机制理解。
