Abstract
The multi-subunit translation initiation factor eIF2B is a control node for protein synthesis. eIF2B activity is canonically modulated through stress-responsive phosphorylation of its substrate eIF2. The eIF2B regulatory subcomplex is evolutionarily related to sugar-metabolizing enzymes, but the biological relevance of this relationship was unknown. To identify natural ligands that might regulate eIF2B, we conduct unbiased binding- and activity-based screens followed by structural studies. We find that sugar phosphates occupy the ancestral catalytic site in the eIF2Bα subunit, promote eIF2B holoenzyme formation and enhance enzymatic activity towards eIF2. A mutant in the eIF2Bα ligand pocket that causes Vanishing White Matter disease fails to engage and is not stimulated by sugar phosphates. These data underscore the importance of allosteric metabolite modulation for proper eIF2B function. We propose that eIF2B evolved to couple nutrient status via sugar phosphate sensing with the rate of protein synthesis, one of the most energetically costly cellular processes.
Highlights
The multi-subunit translation initiation factor Eukaryotic translation initiation factor 2B (eIF2B) is a control node for protein synthesis. eIF2B activity is canonically modulated through stress-responsive phosphorylation of its substrate eukaryotic translation initiation factor 2 (eIF2)
Due to the high protein concentrations required for the MIDAS approach, we focused our efforts on the small 34 kDa eIF2Bα subunit, which can be purified in large quantities and forms a stable homodimer in solution
The guanine nucleotide exchange factor (GEF) catalytic domain is located in the ε subunit, formation of the decameric complex is necessary for full activity, as it forms a scaffold for interaction with its substrate eIF230–33
Summary
The multi-subunit translation initiation factor eIF2B is a control node for protein synthesis. eIF2B activity is canonically modulated through stress-responsive phosphorylation of its substrate eIF2. A mutant in the eIF2Bα ligand pocket that causes Vanishing White Matter disease fails to engage and is not stimulated by sugar phosphates. These data underscore the importance of allosteric metabolite modulation for proper eIF2B function. The resulting decrease in formation of the active eIF2-GTP-Met-tRNAi ternary complex reduces translation initiation and triggers the Integrated Stress Response (ISR). Its activation attenuates bulk protein synthesis while stimulating translation of a subset of transcripts, such as the transcription factor ATF4, that promote adaptation under stress conditions[4,5,6] Both of these ISR effects are important for cells to adapt to acute stress conditions but may lead to dysfunction when chronically engaged. None of these kinases sense carbon or ATP abundance, and phosphorylation itself is an energy-consuming act, an ancient and direct role for eIF2B in energy-sensing is compelling
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