Abstract
Various stressors such as viral infection lead to the suppression of cap-dependent translation and the activation of the integrated stress response (ISR), since the stress-induced phosphorylated eukaryotic translation initiation factor 2 [eIF2(αP)] tightly binds to eIF2B to prevent it from exchanging guanine nucleotide molecules on its substrate, unphosphorylated eIF2. Sandfly fever Sicilian virus (SFSV) evades this cap-dependent translation suppression through the interaction between its nonstructural protein NSs and host eIF2B. However, its precise mechanism has remained unclear. Here, our cryo-electron microscopy (cryo-EM) analysis reveals that SFSV NSs binds to the α-subunit of eIF2B in a competitive manner with eIF2(αP). Together with SFSV NSs, eIF2B retains nucleotide exchange activity even in the presence of eIF2(αP), in line with the cryo-EM structures of the eIF2B•SFSV NSs•unphosphorylated eIF2 complex. A genome-wide ribosome profiling analysis clarified that SFSV NSs expressed in cultured human cells attenuates the ISR triggered by thapsigargin, an endoplasmic reticulum stress inducer. Furthermore, SFSV NSs introduced in rat hippocampal neurons and human induced-pluripotent stem (iPS) cell-derived motor neurons exhibits neuroprotective effects against the ISR-inducing stress. Since ISR inhibition is beneficial in various neurological disease models, SFSV NSs may be a promising therapeutic ISR inhibitor.
Highlights
Various stressors such as viral infection lead to the suppression of cap-dependent translation and the activation of the integrated stress response (ISR), since the stress-induced phosphorylated eukaryotic translation initiation factor 2 [eukaryotic initiation factor 2 (eIF2)(αP)] tightly binds to eIF2B to prevent it from exchanging guanine nucleotide molecules on its substrate, unphosphorylated eIF2
EIF2 is released from the ribosomes as the guanosine disphosphate (GDP)bound form and regenerated by its specific guanine nucleotide exchange factor, eIF2B, a heterodecameric complex of two copies each of the α, β, γ, δ, and ε-subunits[2]
The interfaces for Sandfly fever Sicilian virus (SFSV) NSs partially overlap with those of the phosphorylated eIF2α subunit in the eIF2BeIF2(αP) complex[14], but there are no similarities between phosphorylated eIF2α and SFSV NSs in terms of their three-dimensional structures and interaction modes with eIF2B (Fig. 1b)
Summary
Various stressors such as viral infection lead to the suppression of cap-dependent translation and the activation of the integrated stress response (ISR), since the stress-induced phosphorylated eukaryotic translation initiation factor 2 [eIF2(αP)] tightly binds to eIF2B to prevent it from exchanging guanine nucleotide molecules on its substrate, unphosphorylated eIF2. To understand the effect of the SFSV NSs binding on the eIF2(αP)-mediated eIF2B inhibition, we performed GDP exchange experiments. The suppression was weakened or canceled by the alanine substitutions of the aromatic clusters of SFSV NSs and their effects correlated well with their binding affinities to eIF2B (Fig. 2e).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
