Non-enveloped virus particles (those that lack a lipid-bilayer membrane) must breach the membrane of a target host cell to gain access to its cytoplasm. So far, the molecular mechanism of this membrane penetration step has resisted structural analysis. The spike protein VP4 is a principal component in the entry apparatus of rotavirus, a non-enveloped virus that causes gastroenteritis and kills 440,000 children each year1. Trypsin cleavage of VP4 primes the virus for entry by triggering a rearrangement that rigidifies the VP4 spikes2. We have determined the crystal structure, at 3.2 Å resolution, of the main part of VP4 that projects from the virion. The crystal structure reveals a coiled-coil stabilized trimer. Comparison of this structure with the two-fold clustered VP4 spikes in a ∼12 Å resolution image reconstruction from electron cryomicroscopy of trypsin-primed virions shows that VP4 also undergoes a second rearrangement, in which the oligomer reorganizes and each subunit folds back on itself, translocating a potential membrane-interaction peptide from one end of the spike to the other. This rearrangement resembles the conformational transitions of membrane fusion proteins of enveloped viruses3,4,5,6.
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We thank M. Babyonyshev for technical assistance; T. Yeates for help in analysing the crystal twinning disorder; H. Greenberg for cloned genes and recombinant baculoviruses; E. Vogan for help with data collection and analysis; and the staff of Advanced Photon Source beamline ID-19 (Argonne National Laboratory) and Cornell High Energy Synchrotron Source beamlines F1 and A1. We acknowledge the use of electron cryomicroscopy facilities at the National Center for Macromolecular Imaging funded by NIH at Baylor College of Medicine. This work was supported by an NIH grant and an Ellison Medical Foundation New Investigator in Global Infectious Diseases award to P.R.D., by an NIH grant to B.V.V.P., and by an NIH grant to S.C.H., who is a Howard Hughes Medical Institute Investigator.
Details of the crystallographic structure determination. Includes a description of the twinning disorder in the crystals.
Neutralization escape mutations. Mutations that map to the VP5* fragment are assigned to epitopes based on the VP5CT structure.
Rotavirus VP4 sequences used to assess variability and obtain a consensus sequence. The variability in these sequences is mapped onto the surfaces of the VP8* core and VP5* antigen domain in Fig. 3a, c. The consensus sequence is used to assess the similarity between the VP4 F'G loop and the alphavirus E1 fusion loop in Supplementary Fig. 1.
Alphavirus E1 sequences used to obtain a consensus. The consensus sequence is used to assess the similarity between the VP4 F'G loop and the alphavirus E1 fusion loop in Supplementary Fig. 1.
X-ray diffraction data collection, phasing, and refinement statistics.
About this article
Nature Reviews Microbiology (2012)