Stoichiometry of the eIF2B complex is maintained by mutual stabilization of subunits

Area of Science:

• Molecular Biology
• Cell Biology
• Protein Synthesis Regulation

Background:

• The eukaryotic translation initiation factor 2B (eIF2B) is a vital multi-subunit complex regulating global protein synthesis.
• eIF2B consists of five subunits (α-ε) forming a heterodecamer, and their co-stoichiometric expression is critical for cellular function.
• Understanding the regulation of eIF2B subunit expression is key to comprehending protein synthesis control.

Purpose of the Study:

• To investigate the mechanisms controlling the stoichiometric expression of eIF2B subunits.
• To elucidate how mutual stabilization of eIF2B subunits impacts their expression and assembly.
• To propose a model for the formation of stoichiometric eIF2B complexes.

Main Methods:

• Investigated subunit interactions and expression in human cells.
• Analyzed protein levels and mRNA translation.
• Utilized the ubiquitin-proteasome system as a degradation pathway.

Main Results:

• Stable expression of the eIF2Bε subunit necessitates co-expression of eIF2Bγ.
• Stable expression of the eIF2Bδ subunit requires both eIF2Bβ and eIF2Bγ+ε.
• Subunit expression decreased due to targeted degradation by the ubiquitin-proteasome system, independent of mRNA levels or translation.

Conclusions:

• A model is proposed where mutual stabilization of eIF2B subunits ensures their stoichiometric incorporation into the functional holocomplex.
• This mechanism prevents the accumulation of unstable subunits, maintaining cellular protein synthesis regulation.
• The findings highlight the importance of subunit stoichiometry in the assembly and function of translation initiation factors.