Binding of ISRIB reveals a regulatory site in the nucleotide exchange factor eIF2B

Abstract

The integrated stress response (ISR) is a conserved translational and transcriptional program affecting metabolism, memory, and immunity. The ISR is mediated by stress-induced phosphorylation of eukaryotic translation initiation factor 2α (eIF2α) that attenuates the guanine nucleotide exchange factor eIF2B. A chemical inhibitor of the ISR, ISRIB, reverses the attenuation of eIF2B by phosphorylated eIF2α, protecting mice from neurodegeneration and traumatic brain injury. We describe a 4.1-angstrom-resolution cryo-electron microscopy structure of human eIF2B with an ISRIB molecule bound at the interface between the β and δ regulatory subunits. Mutagenesis of residues lining this pocket altered the hierarchical cellular response to ISRIB analogs in vivo and ISRIB binding in vitro. Our findings point to a site in eIF2B that can be exploited by ISRIB to regulate translation.

Structural basis of eIF2B-catalyzed GDP exchange and phosphoregulation by the integrated stress response

“…S2-S3, Table S1-S3). Clear density for ISRIB indicated that the small molecule retained its symmetric orientation and binding site interactions as previously published (20,21). ISRIB's binding pocket retained two-fold symmetry, unperturbed by asymmetrically bound eIF2 ( Fig.1A, D).…”

“…Structural data show that ISRIB acts as a molecular staple, bridging the symmetric interface of 70 two eIF2B subcomplexes to enhance the formation of the decameric eIF2B holoenzyme (20,21).…”

Norovirus infection results in assembly of virus-specific G3BP1 granules and evasion of eIF2α signaling

“…The absence of canonical SG accumulation during MNV infection, despite a marked translational shut-off and increased eIF2a phosphorylation led us to hypothesize an uncoupling between the P-eIF2a-dependent stress pathways and translation suppression. The inhibitor of the Integrated Stress Response Inhibitor (ISRIB) has previously been shown to reverse the inhibitory impact of P-eIF2a on its recycling factor eIF2B, allowing the exchange between GDP and GTP on phosphorylated substrates, thereby rescuing translation and resolving stress (72,73). To address the downstream activation of P-eIF2a pathway in MNV-infected cells, we measured the effect of ISRIB on translation shut-off, MNV replication and G3BP1 localisation.…”

Structural insights into ISRIB, a memory‐enhancing inhibitor of the integrated stress response

“…This binding site for ISRIB was independently identified and verified [16]. For example, eIF2Bd L179 blocks binding of a methylated ISRIB analog, presumably due to steric hindrance.…”

“…This observation may explain the high efficacy of a di-halogenated ISRIB that can occupy greater space within the binding pocket. This binding site for ISRIB was independently identified and verified [16].…”