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Andrei Korostelev

Andrei Korostelev

UMass Medical School, USA

Title: Conformational dynamics revealed by ensemble cryo-EM

Biography

Biography: Andrei Korostelev

Abstract

Virus propagation depends on efficient synthesis of viral proteins by the host translational machinery. Internal ribosome entry sites (IRESs) of viral mRNAs mediate cap-independent initiation. Intergenic-region (IGR) IRESs of Dicistroviridae family, which includes the Taura syndrome virus (TSV) and Cricket paralysis virus (CrPV), use the most streamlined mechanism of initiation, independent of initiation factors and initiator tRNA. A tRNA-mRNA like pseudoknot of IGR IRESs binds the ribosomal A (aminoacyl-tRNA) site of the 80S ribosome (Fernandez et al., 2014; Koh et al., 2014). The pseudoknot has translocate to the P site to allow binding of the first tRNA and initiate translation.

Using electron cryo-microscopy of a single specimen, we resolved five ribosome structures formed with the Taura syndrome virus IRES and translocase eEF2•GTP bound with sordarin. The structures suggest a trajectory of IRES translocation, required for translation initiation, and provide an unprecedented view of eEF2 dynamics (animation).

The IRES rearranges from extended to bent to extended conformations. This inchworm-like movement is coupled with ribosomal inter-subunit rotation and 40S head swivel. eEF2, attached to the 60S subunit, slides along the rotating 40S subunit to enter the A site. Its diphthamide-bearing tip at domain IV separates the tRNA-mRNA-like pseudoknot I (PKI) of the IRES from the decoding center. This unlocks 40S domains, facilitating head swivel and biasing IRES translocation via hitherto-elusive intermediates with PKI captured between the A and P sites. 

References:

  1. Demo G, Svidritskiy E, Madireddy R, Diaz-Avalos R, Grant T, Grigorieff N, Sousa D, Korostelev AA. Mechanism of ribosome rescue by ArfA and RF2. preprint in bioRxiv. 2016 Dec. 2. (animation)
  2. Loveland AB, Bah E, Madireddy R, Zhang Y, Brilot AF, Grigorieff N, Korostelev AA. Ribosome•RelA structures reveal the mechanism of stringent response activation. eLife. 2016 July 19. (animation) animation)
  3.  Abeyrathne PD, Koh CS, Grant T, Grigorieff N, Korostelev AA. Ensemble cryo-EM uncovers inchworm-like translocation of a viral IRES through the ribosome. eLife. 2016 May 9. (animation)
  4.  Svidritskiy E, Madireddy R, Korostelev AA. Structural Basis for Translation Termination on a Pseudouridylated Stop Codon. J Mol Biol. 2016 Apr 20.
  5. Svidritskiy E, Korostelev AA. Ribosome Structure Reveals Preservation of Active Sites in the Presence of a P-Site Wobble Mismatch. Structure. 2015 Nov 3;23(11):2155-61.