Abstract

Viral infections during pregnancy are a significant cause of infant morbidity and mortality. Of these, rubella virus infection is a well-substantiated example that leads to miscarriages or severe fetal defects. However, structural information about the rubella virus has been lacking due to the pleomorphic nature of the virions. Here we report a helical structure of rubella virions using cryo-electron tomography. Sub-tomogram averaging of the surface spikes established the relative positions of the viral glycoproteins, which differed from the earlier icosahedral models of the virus. Tomographic analyses of in vitro assembled nucleocapsids and virions provide a template for viral assembly. Comparisons of immature and mature virions show large rearrangements in the glycoproteins that may be essential for forming the infectious virions. These results present the first known example of a helical membrane-enveloped virus, while also providing a structural basis for its assembly and maturation pathway.

Highlights

  • Rubella virus is an airborne human pathogen that causes a contagious disease with measleslike symptoms in children and adults

  • Rubella virus (RV) causes serious fetal defects when contracted during pregnancy

  • Subsequent local averaging of the RV surface spikes has established the conformations of its immunogenic glycoproteins

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Summary

Introduction

Rubella virus is an airborne human pathogen that causes a contagious disease with measleslike symptoms in children and adults. E1 is responsible for recognition and attachment to cellular receptors [9] It is involved in membrane fusion in the presence of low pH and calcium ions [10,11,12]. The rubella E1 ectodomain has an elongated structure, similar to the post-fusion conformations of the alphavirus E1 and flavivirus E glycoproteins [13]. The third structural protein of rubella virus is the capsid protein, which interacts via its amino-terminal domain with the viral RNA genome to form the inner nucleocapsid [6, 14]. The atomic structure of the carboxy-terminal domain of the capsid protein is known [16] and presumably forms the structural framework of the viral nucleocapsid

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