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Crystal structure of the Rubella virus glycoprotein E1 in its post-fusion form crystallized in presence of 1mM of calcium acetate
Structural highlights
FunctionPOLS_RUBVM Capsid protein interacts with genomic RNA and assembles into icosaedric core particles. The resulting nucleocapsid eventually associates with the cytoplasmic domain of E2 at the cell membrane, leading to budding and formation of mature virions. Phosphorylation negatively regulates RNA-binding activity, possibly delaying virion assembly during the viral replication phase. Capsid protein dimerizes and becomes disulfide-linked in the virion, but this interaction seems not to be important for its biological function. Modulates genomic RNA replication. Modulates subgenomic RNA synthesis by interacting with human C1QBP/SF2P32. Induces both perinuclear clustering of mitochondria and the formation of electron-dense intermitochondrial plaques, both hallmarks of rubella virus infected cells. Induces apoptosis when expressed in transfected cells. E2 envelope glycoprotein is responsible for viral attachment to target host cell, by binding to the cell receptor. Its transport to the plasma membrane depends on interaction with E1 protein. E1 envelope glycoprotein is a class II viral fusion protein. Fusion activity is inactive as long as E1 is bound to E2 in mature virion. After virus attachment to target cell and clathrin-mediated endocytosis, acidification of the endosome would induce dissociation of E1/E2 heterodimer and concomitant trimerization of the E1 subunits. This E1 homotrimer is fusion active, and promotes release of viral nucleocapsid in cytoplasm after endosome and viral membrane fusion (By similarity). E1 cytoplasmic tail modulates virus release, and the tyrosines residues are critical for this function. Publication Abstract from PubMedLittle is known about the three-dimensional organization of rubella virus, which causes a relatively mild measles-like disease in children but leads to serious congenital health problems when contracted in utero. Although rubella virus belongs to the same family as the mosquito-borne alphaviruses, in many respects it is more similar to other aerosol-transmitted human viruses such as the agents of measles and mumps. Although the use of the triple MMR (measles, mumps and rubella) live vaccine has limited its incidence in western countries, congenital rubella syndrome remains an important health problem in the developing world. Here we report the 1.8 A resolution crystal structure of envelope glycoprotein E1, the main antigen and sole target of neutralizing antibodies against rubella virus. E1 is the main player during entry into target cells owing to its receptor-binding and membrane-fusion functions. The structure reveals the epitope and the neutralization mechanism of an important category of protecting antibodies against rubella infection. It also shows that rubella virus E1 is a class II fusion protein, which had hitherto only been structurally characterized for the arthropod-borne alphaviruses and flaviviruses. In addition, rubella virus E1 has an extensive membrane-fusion surface that includes a metal site, reminiscent of the T-cell immunoglobulin and mucin family of cellular proteins that bind phosphatidylserine lipids at the plasma membrane of cells undergoing apoptosis. Such features have not been seen in any fusion protein crystallized so far. Structural comparisons show that the class II fusion proteins from alphaviruses and flaviviruses, despite belonging to different virus families, are closer to each other than they are to rubella virus E1. This suggests that the constraints on arboviruses imposed by alternating cycles between vertebrates and arthropods resulted in more conservative evolution. By contrast, in the absence of this constraint, the strictly human rubella virus seems to have drifted considerably into a unique niche as sole member of the Rubivirus genus. Functional and evolutionary insight from the crystal structure of rubella virus protein E1.,Dubois RM, Vaney MC, Tortorici MA, Kurdi RA, Barba-Spaeth G, Krey T, Rey FA Nature. 2013 Jan 6. doi: 10.1038/nature11741. PMID:23292515[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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