Functional molecular mapping of archaeal translation initiation factor 2

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Eukaryotic and archaeal initiation factors 2 (e/aIF2) are essential heterotrimeric proteins (αβγ) for protein synthesis.
• These factors deliver methionylated initiator tRNA (Met-tRNAiMet) to the ribosome's small subunit.
• The structure of archaeal aIF2γ from Pyrococcus abyssi, the core subunit, is known and resembles elongation factor EF1-A.

Purpose of the Study:

• To elucidate the specific roles of each aIF2 subunit (α, β, γ) in binding Met-tRNAiMet.
• To identify the molecular determinants responsible for Met-tRNAiMet recognition by aIF2.
• To understand the contribution of individual aIF2 domains to tRNA binding and complex formation.

Main Methods:

• Biochemical assays to study tRNA binding affinities.
• Site-directed mutagenesis to probe subunit interactions and functional domains.
• Analysis of various aminoacyl-tRNA ligands to determine recognition specificity.

Main Results:

• The methionyl group on tRNA is a key determinant for aIF2 recognition.
• aIF2γ alone binds Met-tRNAiMet with reduced affinity compared to the intact trimer.
• aIF2α significantly enhances tRNA binding affinity, with its C-domain mediating interaction with aIF2γ and restoring full binding capacity.
• The N-domain of aIF2α exhibits non-specific RNA interaction, suggesting a potential role in ribosome binding.

Conclusions:

• The aIF2 complex achieves high affinity for Met-tRNAiMet through the cooperative action of its subunits, particularly aIF2α.
• The C-domain of aIF2α is critical for both γ subunit interaction and overall tRNA binding efficiency.
• The non-specific RNA binding of aIF2α's N-domain may facilitate the recruitment of the aIF2-tRNA complex to the small ribosomal subunit.