Sugar phosphate activation of the stress sensor eIF2B

Area of Science:

• Molecular Biology
• Biochemistry
• Cellular Metabolism

Background:

• The eukaryotic translation initiation factor 2B (eIF2B) is a crucial regulator of protein synthesis.
• eIF2B activity is primarily controlled by the phosphorylation of its substrate, eIF2, in response to cellular stress.
• The regulatory subcomplex of eIF2B shares evolutionary links with sugar-metabolizing enzymes, suggesting a potential role for metabolites in its regulation.

Purpose of the Study:

• To identify natural ligands that regulate the activity of the translation initiation factor eIF2B.
• To investigate the biological relevance of the evolutionary relationship between eIF2B and sugar-metabolizing enzymes.
• To elucidate the mechanism by which metabolites might control protein synthesis.

Main Methods:

• Unbiased binding and activity-based screens were employed to identify eIF2B ligands.
• Structural studies were conducted to determine the binding mode of identified ligands.
• Biochemical assays were used to assess the impact of ligands on eIF2B activity.
• Analysis of a patient-derived mutant in the eIF2Bα subunit was performed.

Main Results:

• Sugar phosphates were identified as natural ligands that bind to the ancestral catalytic site of the eIF2Bα subunit.
• Binding of sugar phosphates promotes the formation of the eIF2B holoenzyme and enhances its enzymatic activity towards eIF2.
• A disease-associated mutation in the eIF2Bα ligand pocket prevents sugar phosphate binding and stimulation, indicating impaired allosteric regulation.
• These findings highlight the importance of metabolite binding for eIF2B function.

Conclusions:

• The multi-subunit translation initiation factor eIF2B is allosterically regulated by sugar phosphates.
• eIF2B likely evolved to sense nutrient availability through sugar phosphate binding, thereby coupling metabolic status to the rate of protein synthesis.
• Dysregulation of this metabolite-sensing mechanism, as seen in Vanishing White Matter disease, can impair protein synthesis and cellular function.