Structural insight into the eIF2-eIF2B interaction

Abstract

eIF2B (eukaryotic initiation factor 2B) is a key regulator of translation initiation. It catalyzes guanine nucleotide exchange on eIF2, which delivers the methionylated initiator tRNA to the 40S ribosomal subunit. This exchange reaction is inhibited by the stress-induced phosphorylation of the eIF2 alpha subunit, which leads to global repression of cellular protein synthesis. eIF2B is composed of five subunits. The catalytic gamma/epsilon subcomplex is responsible for nucleotide exchange, while the regulatory alpha/beta/delta subcomplex discriminates the phosphorylation status of the eIF2 alpha subunit. We established a bacterial expression system for eIF2B, and determined its crystal structure at 3.2 Å resolution. The crystal structure revealed that eIF2B is a decamer containing two molecules of each subunit. The hexameric regulatory subcomplex is formed by the trimerization of one alpha-alpha homodimer unit and two beta-delta heterodimer units, and two catalytic subcomplexes are individually connected to the regulatory subcomplex through two beta-delta heterodimer units. Photo-cross-linking analyses showed that the N-terminal domain of the eIF2 alpha subunit, which bears the phosphorylation site, is recognized by a composite surface formed by the eIF2B alpha, beta, and delta subunits. Based on these results, we report structural insights into the interaction between eIF2 and eIF2B.

eIF2B bodies and their role in the integrated stress response

“…eIF2Bɛ was shown to co-localise with SGs in embryonic mouse cells (Kimball et al, 2003) however more recent studies in yeast suggest eIF2B localises to foci distinct from SGs (Moon and Parker, 2018). In keeping with this, the data presented here demonstrates that mammalian eIF2B bodies are spatially discrete from SGs (Figure 3.6, In its native form eIF2B exists as a heterodecamer (Gordiyenko et al, 2014;Kashiwagi et al, 2016;Kashiwagi et al, 2017;Wortham et al, 2014), however subcomplexes of eIF2B have also been found to exist in mammalian cells, namely eIF2B(βδγε) tetramers and eIF2B(γε) heterodimers (Wortham et al, 2014). The data presented in this study highlight an increased complexity of the localisation of eIF2B within mammalian cells when compared to yeast.…”

Binding of the integrated stress response inhibitor, ISRIB, reveals a regulatory site in the nucleotide exchange factor, elF2B

“…The regulatory and catalytic subunits of eIF2B evolved from ligand regulated protein ancestors. ADP-glucose pyrophosphorylase has a nucleotide bind site that is conserved in its descendant catalytic γ and ε subunits, whereas ribose-1,5bisphosphate isomerase has a phospho-sugar binding pocket conserved in its descendant α, β and δ regulatory subunits (reviewed in Kuhle et al, 2015;Kashiwagi et al, 2017). The ISRIB binding pocket discovered here represents a third conserved feature of eIF2B.…”

“…Genetic and structural observations indicate that the inhibitory effect of eIF2(αP) on eIF2B arises from the engagement by the α subunit of eIF2 at a cavity formed by the convergence of the α, β and δ regulatory subunits of the eIF2B decamer (Vazquez de Aldana and Hinnebusch, 1994;Pavitt et al, 1997;Kashiwagi et al, 2016;Bogorad et al, 2017). This regulatory site is distant from the catalytic γε subcomplex of eIF2B and its consecutive Asn-Phe residues that engage the nucleotide binding γ subunit of eIF2 to effect nucleotide exchange (Kashiwagi et al, 2016;Kashiwagi et al, 2017).…”

“…An interaction of ISRIB with eIF2B is also consistent with the finding that the eIF2B decamer isolated from ISRIB-treated cells (or cell lysates) is more stable in a density gradient than eIF2B from untreated cells (Sidrauski et al, 2015b', figure 3 therein). However, the ISRIB-resistant mutations identified to date cluster at a distance from both the regulatory site engaged by eIF2(αP) and the catalytic site engaged by eIF2γ (Kashiwagi et al, 2016;Kashiwagi et al, 2017). Thus, whilst the bulk of the evidence suggests that ISRIB binds eIF2B to regulate its activity, indirect modes of action are not excluded.…”

The FEBS Journal past … and present

“…who invites authors to provide a succinct discussion of a structure recently published by their laboratory. Amongst other excellent content are gems by Kashiwagi, Ito and Yokoyama on the crustal structure of eIF2B and by Sasaki, Senda and colleagues on a structural reverse genetics approach to understanding PI5P4Kβ activity . http://febs.onlinelibrary.wiley.com/hub/issue/10.1002/(ISSN)1742-4658(CAT)FreeReviewContent(VI)Viewpoints/ are commissioned by Viewpoints Advisory Editors Colin Adrain (Gulbenkian Institute).…”