Abstract
Colony collapse disorder (CCD) is a multi‐faceted syndrome decimating bee populations worldwide, and a group of viruses of the widely distributed Dicistroviridae family have been identified as a causing agent of CCD. This family of viruses employs non‐coding RNA sequences, called internal ribosomal entry sites (IRESs), to precisely exploit the host machinery for viral protein production. Using single‐particle cryo‐electron microscopy (cryo‐EM), we have characterized how the IRES of Israeli acute paralysis virus (IAPV) intergenic region captures and redirects translating ribosomes toward viral RNA messages. We reconstituted two in vitro reactions targeting a pre‐translocation and a post‐translocation state of the IAPV‐IRES in the ribosome, allowing us to identify six structures using image processing classification methods. From these, we reconstructed the trajectory of IAPV‐IRES from the early small subunit recruitment to the final post‐translocated state in the ribosome. An early commitment of IRES/ribosome complexes for global pre‐translocation mimicry explains the high efficiency observed for this IRES. Efforts directed toward fighting CCD by targeting the IAPV‐IRES using RNA‐interference technology are underway, and the structural framework presented here may assist in further refining these approaches.
Highlights
Apis mellifera, the common western honey bee, is affected worldwide by an enigmatic syndrome characterized by a drastic disappearance of the workforce, causing the accelerated collapse of the hive (Ratnieks & Carreck, 2010)
The prototypical architecture of the type IV internal ribosomal entry sites (IRESs) family consisting of three nested pseudoknots is extended by a 50 terminal stem loop (SL-VI) proposed to play functional roles in the early positioning of the Israeli acute paralysis virus (IAPV)-IRES in the ribosome (Schuler et al, 2006; Au et al, 2018)
Two unpaired adenine residues are placed in a strategic position at the core of the three-way helical junction connecting stem loop III (SL-III), the anti-codon stem loop (ASL)-like element of the pseudoknot I (PKI), and the double-helical segment connecting PKI and PKIII
Summary
The common western honey bee, is affected worldwide by an enigmatic syndrome characterized by a drastic disappearance of the workforce, causing the accelerated collapse of the hive (Ratnieks & Carreck, 2010). Though the exact etiology of CCD is unknown (Anderson & East, 2008), a group of viruses belonging to the Dicistroviridae family were found in metagenomic studies of CCD-affected hives (CoxFoster et al, 2007; Chen et al, 2014). Among this group of viruses, the Israeli acute paralysis virus (IAPV) showed a strong correlation with CCD, revealing a prominent role in the development of the syndrome (Hou et al, 2014; Doublet et al, 2017). ORF2 encodes a single poly-protein that, upon proteolytic digestion, generates the structural proteins that will eventually compose the viral capsid (Kerr & Jan, 2016; Mullapudi et al, 2017)
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