Archaeal aIF2B interacts with eukaryotic translation initiation factors eIF2alpha and eIF2Balpha: Implications for...

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Eukaryotic translation initiation is regulated by phosphorylation of eukaryotic initiation factor 2 alpha-subunit (eIF2α), inhibiting eIF2B.
• The N-terminal S1 domain of phosphorylated eIF2α interacts with the eIF2B regulatory subcomplex (α/GCN3, β/GCD7, δ/GCD2), blocking catalytic activity.

Purpose of the Study:

• To investigate the functional homology between archaeal proteins and eukaryotic eIF2B regulatory subunits.
• To explore the evolutionary conservation of translation initiation regulation.

Main Methods:

• Sequence analysis to identify archaeal initiation factor 2B (aIF2B) homologs.
• In vitro binding assays to test interactions between archaeal and eukaryotic factors.
• Mass spectrometry to identify co-purifying proteins.
• Structural modeling of the eIF2B regulatory subcomplex.

Main Results:

• Archaeal proteins, designated aIF2Bs, were predicted as functional homologs of eIF2B regulatory subunits.
• aIF2B proteins bind to archaeal aIF2α and, in one case, to yeast eIF2α S1 domain.
• Interactions were observed independent of eIF2α phosphorylation.
• Mass spectrometry identified aIF2α and other proteins co-purifying with aIF2B.
• A structural model of the eIF2B regulatory subcomplex was built based on aIF2B crystal structure.

Conclusions:

• aIF2B proteins share functional roles with eukaryotic eIF2B regulatory subunits.
• Conserved binding surfaces for eIF2α exist in the regulatory subcomplex across archaea and eukaryotes.
• This suggests conserved mechanisms in translation initiation regulation.