Structure of the nucleotide exchange factor eIF2B reveals mechanism of memory-enhancing molecule

Abstract

Abstract:Regulation by the integrated stress response (ISR) converges on the phosphorylation of translation initiation factor eIF2 in response to a variety of stresses. Phosphorylation converts eIF2 from substrate to competitive inhibitor of its dedicated guanine nucleotide exchange factor, eIF2B, inhibiting translation. ISRIB, a drug-like eIF2B activator, reverses the effects of eIF2 phosphorylation and, remarkably, in rodents enhances cognition and corrects cognitive deficits after brain injury. To determine its mechanism of action, we solved an atomic-resolution structure of ISRIB bound in a deep cleft within decameric human eIF2B by electron cryomicroscopy. Structural and biochemical analyses revealed that formation of fully active, decameric eIF2B holoenzyme depended on the assembly of two identical tetrameric subcomplexes, and that ISRIB promoted this step by cross-bridging a central symmetry interface. Regulation of eIF2B assembly emerges as a rheostat for eIF2B activity that tunes translation during the ISR and that can be further modulated by ISRIB.peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission.The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/222257 doi: bioRxiv preprint first posted online Nov. 22, 2017; Main Text:Protein quality control is essential to the maintenance of cellular and organismal health. To prevent the production of deleterious proteins, such as those from invading viruses or those produced in misfolding-prone environments, cells regulate protein synthesis. By arresting or accelerating the cardinal decision of translation initiation, cells effect proteome-wide changes that drive organismal functions, such as development, memory, and immunity (1-3).A key enzyme in the regulation of protein synthesis is eukaryotic translation initiation factor 2B (eIF2B), a dedicated guanine nucleotide exchange factor (GEF) for translation initiation factor 2 (eIF2). eIF2B is composed of five subunits (α,β,γ,δ,ε) that assemble into a decamer composed of two copies of each subunit (4-8). The eIF2Bε subunit contains the enzyme's catalytic center and associates closely with eIF2Bγ (9). Two copies each of the structurally homologous eIF2Bα, β, and δ subunits form the regulatory core that modulates eIF2B's catalytic activity (10-12).eIF2B's substrate, eIF2 is composed of three subunits (α,β,γ) and binds methionine initiator tRNA and GTP to form the ternary complex required to initiate translation on AUG start codons. eIF2's γ subunit contains the GTP-binding pocket (as reviewed in (13, 14)).In response to various inputs, many of which are cell stresses, phosphorylation of eIF2α at serine 51 converts eIF2 from a substrate for nucleotide exchange to a competitive inhibitor of eIF2B.Phosphorylated eIF2 binds to eIF2B with enhanced affinity, effectively sequestering the limiting eIF2B complex from engaging unphosphorylated eIF2 for nucleotide exchange (10-12). Such inhibition leads to an attenuation of general translation and, paradox...

Pharmacologic Activation of a Compensatory Integrated Stress Response Kinase Promotes Mitochondrial Remodeling in PERK-deficient Cells

“…4A,B). Further, the increase in elongated mitochondria observed in Tg-treated Perk +/+ MEFs was inhibited by co-treatment with ISRIB -an ISR inhibitor that binds to eIF2B and desensitizes cells to eIF2a phosphorylation (Sidrauski et al, 2013;Tsai et al, 2018;Zyryanova et al, 2018). These results confirm that the mitochondria elongation observed in Tg-treated cells is attributed to PERKdependent ISR signaling.…”

DNL343 is an investigational CNS penetrant eIF2B activator that prevents and reverses the effects of neurodegeneration caused by the Integrated Stress Response

“…In contrast, eIF2B activators have proven to be well tolerated in animal models while also improving memory and neurological deficits (Sidrauski, Acosta-Alvear et al 2013, Chou, Krukowski et al 2017, Abbink, Wisse et al 2019, Wong, LeBon et al 2019, Krukowski, Nolan et al 2020 ). The first published eIF2B activator, ISRIB, binds to and stabilizes the eIF2B complex in its decameric form and promotes the GEF activity of eIF2B regardless of the presence of phosphorylated eIF2 (Tsai, Miller-Vedam et al 2018, Zyryanova, Weis et al 2018 ). ISRIB and its analog, 2BAct, were also neuroprotective in an eIF2B mutant mouse model of VWMD that displays ISR-mediated neurodegeneration (Abbink, Wisse et al 2019, Wong, LeBon et al 2019.…”