Abstract
Simple RNA animal viruses generally enter cells through receptor-mediated endocytosis followed by acid pH dependent release and translocation of RNA across the endosomal membrane. The T = 3 nodaviruses contain prefabricated pentameric helical bundles that are cleaved from the remainder of the subunits by an assembly-dependent auto-proteolysis and they are positioned for release through 5-fold axes of the particle. We previously proposed that these bundles may serve as conduits for RNA membrane translocation. Additional support for this hypothesis is now provided by the first atomic resolution structure of a T = 4 RNA virus, where we find cleavage sites and helical bundles nearly identical with those observed in T = 3 nodaviruses. The helices are of sufficient length to span a membrane bilayer and the internal diameter of the coiled bundle could accommodate ssRNA. The T = 4 particle has a mean outer diameter of 410 Å and is formed by 240 copies of a single subunit type. The subunit is composed of a helical inner domain (where the cleavage occurs) containing residues preceding and following a canonical, viral, eight-stranded β-sandwich that forms the contiguous shell. Inserted between two strands of the shell domain are 133 residues with an immunoglobulin c-type fold. The initial gene product consists of 644 amino acid residues and is cleaved between residues Asn570 and Phe571 in the mature particle determined in this analysis.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1-10 |
| Number of pages | 10 |
| Journal | Journal of Molecular Biology |
| Volume | 261 |
| Issue number | 1 |
| DOIs | |
| State | Published - Aug 9 1996 |
| Externally published | Yes |
Bibliographical note
Funding Information:We thank Professor Donald Hendry at Rhodes University, Grahamstown, South Africa for providing the virus samples, Tim Schmidt for help in data collection and processing and Michael Rossmann for stimulating discussions regarding phase determination and refinement. We thank the staff at the Purdue University Computing Center and Robert Martino at the National Institutes of Health for their help with the computational problems. X-ray data were collected on beamlines A1 and F1 at the Cornell High Energy Synchrotron Source and on beamline X12c, at the National Synchrotron Light source, Brookhaven National Laboratories. We deeply appreciate the help of the staff at those facilities. Figures 1 and 4 were generated with program MOLSCRIPT (Kraulis, 1991) and Figure 2 with Program MOLVIEW (Smith, 1993). This work was supported by a grant from the US National Institutes of Health (R01 GM 34220-10) and the Markey Charitable Trust.
Keywords
- Ig-fold
- Jelly-roll
- Membrane translocation
- Quasi-equivalence
- Tetraviruses
- Viruses