Near-Atomic Resolution Structure Determination of a Cypovirus Capsid and Polymerase Complex Using Cryo-EM at 200kV

J Mol Biol. 2017 Jan 6;429(1):79-87. doi: 10.1016/j.jmb.2016.11.025. Epub 2016 Dec 1.

Abstract

Single-particle cryo-electron microscopy (cryo-EM) allows the high-resolution structural determination of biological assemblies in a near-native environment. However, all high-resolution (better than 3.5Å) cryo-EM structures reported to date were obtained by using 300kV transmission electron microscopes (TEMs). We report here the structures of a cypovirus capsid of 750-Å diameter at 3.3-Å resolution and of RNA-dependent RNA polymerase (RdRp) complexes within the capsid at 3.9-Å resolution using a 200-kV TEM. The newly resolved structure revealed conformational changes of two subdomains in the RdRp. These conformational changes, which were involved in RdRp's switch from non-transcribing to transcribing mode, suggest that the RdRp may facilitate the unwinding of genomic double-stranded RNA. The possibility of 3-Å resolution structural determinations for biological assemblies of relatively small sizes using cryo-EM at 200kV was discussed.

Keywords: RNA polymerase; accelerating voltage; cryo-EM; phase residual distribution; reovirus.

MeSH terms

  • Capsid / ultrastructure*
  • Cryoelectron Microscopy*
  • Macromolecular Substances / ultrastructure*
  • Models, Molecular
  • Protein Conformation
  • RNA, Viral / metabolism
  • RNA-Dependent RNA Polymerase / chemistry*
  • RNA-Dependent RNA Polymerase / metabolism
  • RNA-Dependent RNA Polymerase / ultrastructure*
  • Reoviridae / enzymology
  • Reoviridae / metabolism
  • Reoviridae / ultrastructure*

Substances

  • Macromolecular Substances
  • RNA, Viral
  • RNA-Dependent RNA Polymerase