Allosteric regulation of eIF2B activity and the Integrated Stress Response is controlled by a protrusive α-helix in eIF2B β (the 'latch-helix') that locks onto eIF2B α to stabilize the active state, with eIF2-P binding unhooking this latch to induce the inhibited state, while structurally unrelated viral effector proteins have convergently evolved to stabilize the latched active state, and rational drug design exploiting this mechanism enables creation of compounds that either activate or inhibit the ISR by targeting distinct conformational states of the eIF2B complex.

The ternary complex (TC), composed of translation initiation factor eIF2, GTP, and initiator methionyl tRNA, delivers the first amino acid to the ribosome to initiate protein synthesis. The activity of the decameric eukaryotic initiation factor 2B complex (eIF2B) initiates TC assembly by catalyzing GDP to GTP exchange on eIF2, thereby setting the TC levels in the cell. Stress-induced phosphorylation converts eIF2 from the substrate of the GDP/GTP exchange reaction into an inhibitor (eIF2-P) of eIF2B. This conversion reduces the cell’s TC levels and induces the widespread reprogramming of translation known as the Integrated Stress Response (ISR). Here, we chart an allosteric axis running through eIF2B, revealing the importance of a protrusive α-helix in its β-subunit, the ‘latch-helix’, that locks onto the α-subunit to induce eIF2B activity. eIF2-P binding unhooks the latch-helix, opening eIF2B, which inhibits its GDP/GTP exchange activity. Distinct viral proteins have convergently evolved to bind to eIF2Bα and stabilize the latch-helix-bound active state. Using these insights, we generated ISR-ACTivating compounds, ISRACTs, that stabilize eIF2B in its inhibited, unlatched state. Our study thus highlights how state-transitions in eIF2B are regulated via long-range allostery.