Structure and dimerization of translation initiation factor aIF5B in solution

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Translation initiation factor 5B (IF5B) is crucial for initiating protein synthesis.
• Understanding the solution structure of archaeal IF5B (aIF5B) is key to elucidating its function.
• Previous studies indicated potential monomeric and dimeric forms of aIF5B.

Purpose of the Study:

• To determine the solution structure of archaeal IF5B (aIF5B).
• To investigate the monomer-dimer equilibrium of aIF5B in solution.
• To compare the solution structure with the known crystal structure.

Main Methods:

• Small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) were used to analyze aIF5B.
• Sedimentation equilibrium (SE) and sedimentation velocity (SV) analytical ultracentrifugation (AUC) characterized the solution species.
• Crystallographic structure was used to model and compute theoretical sedimentation coefficients.

Main Results:

• aIF5B exists in both monomeric and dimeric forms in solution, with dimers being irreversible but comprising a small percentage (5.0-6.8%).
• Sedimentation coefficients for monomer and dimer were determined as 3.64 S and 5.51 S, respectively, aligning with theoretical models.
• SAXS data, particularly with glycerol to inhibit dimerization, confirmed a solution structure similar to the crystal structure, revealing an elongated conformation (Rg=37.5 Å, Dmax≈130 Å).

Conclusions:

• The solution structure of aIF5B is highly consistent with its atomic resolution crystal structure.
• Glycerol effectively inhibits aIF5B dimerization, allowing for the study of the monomeric form.
• Structural differences exist between archaeal IF5B and its homolog, E. coli IF2.