Dubé Mathieu, Rey Felix A, Kielian Margaret
Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York, United States of America.
Unité de Virologie Structurale, Institut Pasteur and CNRS UMR 3569, Paris, France.
PLoS Pathog. 2014 Dec 4;10(12):e1004530. doi: 10.1371/journal.ppat.1004530. eCollection 2014 Dec.
Rubella virus (RuV) infection of pregnant women can cause fetal death, miscarriage, or severe fetal malformations, and remains a significant health problem in much of the underdeveloped world. RuV is a small enveloped RNA virus that infects target cells by receptor-mediated endocytosis and low pH-dependent membrane fusion. The structure of the RuV E1 fusion protein was recently solved in its postfusion conformation. RuV E1 is a member of the class II fusion proteins and is structurally related to the alphavirus and flavivirus fusion proteins. Unlike the other known class II fusion proteins, however, RuV E1 contains two fusion loops, with a metal ion complexed between them by the polar residues N88 and D136. Here we demonstrated that RuV infection specifically requires Ca(2+) during virus entry. Other tested cations did not substitute. Ca(2+) was not required for virus binding to cell surface receptors, endocytic uptake, or formation of the low pH-dependent E1 homotrimer. However, Ca(2+) was required for low pH-triggered E1 liposome insertion, virus fusion and infection. Alanine substitution of N88 or D136 was lethal. While the mutant viruses were efficiently assembled and endocytosed by host cells, E1-membrane insertion and fusion were specifically blocked. Together our data indicate that RuV E1 is the first example of a Ca(2+)-dependent viral fusion protein and has a unique membrane interaction mechanism.
孕妇感染风疹病毒（RuV）可导致胎儿死亡、流产或严重的胎儿畸形，在许多欠发达地区，这仍然是一个重大的健康问题。风疹病毒是一种小型包膜RNA病毒，通过受体介导的内吞作用和低pH依赖性膜融合感染靶细胞。风疹病毒E1融合蛋白的结构最近已解析出其融合后构象。风疹病毒E1是II类融合蛋白的成员，在结构上与甲病毒和黄病毒融合蛋白相关。然而，与其他已知的II类融合蛋白不同，风疹病毒E1含有两个融合环，它们之间通过极性残基N88和D136络合一个金属离子。在此，我们证明风疹病毒感染在病毒进入过程中特别需要Ca2+。其他测试的阳离子不能替代。Ca2+对于病毒与细胞表面受体的结合、内吞摄取或低pH依赖性E1同三聚体的形成不是必需的。然而，Ca2+是低pH触发的E1脂质体插入、病毒融合和感染所必需的。N88或D136的丙氨酸替代是致死性的。虽然突变病毒能被宿主细胞有效组装和内吞，但E1膜插入和融合被特异性阻断。我们的数据共同表明，风疹病毒E1是Ca2+依赖性病毒融合蛋白的首个例子，并且具有独特的膜相互作用机制。
