A central helical switch controls integrated stress response signaling via eIF2B conformation and assembly.

Abstract

In response to a variety of biological stressors, the Integrated Stress Response (ISR) tunes down translation and activates expression of stress-responsive factors that enable a return to homeostasis. ISR signaling is coordinated by eIF2B, a decameric guanine nucleotide exchange factor whose activity level dictates ISR signaling outcomes. Distinct dynamic conformational and assembly transitions regulate eIF2B activity. The underlying allosteric mechanisms that enable these dynamic transitions were not understood. Using a combination of hydrogen deuterium exchange-mass spectrometry and cryo-EM, we identified a helical switch whose orientation determines global eIF2B conformation. Furthermore, this switch (Switch-Helix) is triggered upon eIF2B assembly transitions. eIF2B activity and ISR signaling outcomes can be controlled by rationally designed Switch-Helix mutations. Collectively, we identify the Switch-Helix as a fulcrum of eIF2B conformational transitions and a highly conserved determinant of ISR signaling state. This work both defines an allosteric mechanism of dynamic eIF2B conformational and assembly transitions and unlocks new strategies for designing therapeutics for the broad range of diseases characterized by aberrant ISR signaling.