Calcium-Dependent Rubella Virus Fusion Occurs in Early Endosomes
Calcium-Dependent Rubella Virus Fusion Occurs in Early Endosomes
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DOI：
10.1128/jvi.00634-16
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发表时间：
2016-07-01
影响因子：
5.4
通讯作者：
Kielian, Margaret
中科院分区：
文献类型：
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作者：
Dube, Mathieu;Etienne, Loic;Kielian, Margaret
风疹病毒E1膜蛋白(RUV)是一种结构上与甲型病毒、黄病毒和细小病毒的融合蛋白相关的II类膜融合蛋白。病毒的侵入是由低pH依赖的融合反应介导的，通过E1‘S插入细胞膜并重新折叠成稳定的同源三聚体。与其他描述的II类蛋白不同，RUV E1包含2个融合环，通过与N88和D136残基相互作用，使它们之间的金属离子复杂化。E1蛋白插入靶膜、融合和感染需要钙，并被N88或D136的丙氨酸取代所阻止。在这里，我们讨论了E1对钙结合的需求，以及病毒进入时钙需求的细胞内位置。我们的结果表明，N88和D136是支持RUV融合的最佳配置，并且在病毒生命周期中被强烈选择。虽然E1与结合钙和阴离子脂类的细胞蛋白有一些相似之处，但RUV与膜的结合不依赖于阴离子脂类。病毒融合发生在早期内小体内，细胞内钙离子的螯合表明早期内小体内的钙是病毒融合和感染所必需的。在中性pH条件下，钙离子触发了E1可逆插入靶膜，但E1同源三聚体的形成和融合需要较低的pH。因此，与其他已知的II类融合蛋白不同，RUV E1具有不同的触发机制，分别由内体钙和低pH介导的膜插入和融合蛋白复性。
The E1 membrane protein of rubella virus (RuV) is a class II membrane fusion protein structurally related to the fusion proteins of the alphaviruses, flaviviruses, and phleboviruses. Virus entry is mediated by a low pH-dependent fusion reaction through E1's insertion into the cell membrane and refolding to a stable homotrimer. Unlike the other described class II proteins, RuV E1 contains 2 fusion loops, which complex a metal ion between them by interactions with residues N88 and D136. Insertion of the E1 protein into the target membrane, fusion, and infection require calcium and are blocked by alanine substitution of N88 or D136. Here we addressed the requirements of E1 for calcium binding and the intracellular location of the calcium requirement during virus entry. Our results demonstrated that N88 and D136 are optimally configured to support RuV fusion and are strongly selected for during the virus life cycle. While E1 has some similarities with cellular proteins that bind calcium and anionic lipids, RuV binding to the membrane was independent of anionic lipids. Virus fusion occurred within early endosomes, and chelation of intracellular calcium showed that calcium within the early endosome was required for virus fusion and infection. Calcium triggered the reversible insertion of E1 into the target membrane at neutral pH, but E1 homotrimer formation and fusion required a low pH. Thus, RuV E1, unlike other known class II fusion proteins, has distinct triggers for membrane insertion and fusion protein refolding mediated, respectively, by endosomal calcium and low pH.