Folding transitions during assembly of the eukaryotic mRNA cap-binding complex

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• The cap-binding protein eukaryotic translation initiation factor 4E (eIF4E) is crucial for cap-dependent translation initiation.
• eIF4E binds the mRNA 5' cap and the adaptor protein eIF4G, facilitating ribosome recruitment.
• Understanding eIF4E's conformational changes is key to deciphering translation regulation.

Purpose of the Study:

• To investigate the structural dynamics of apo-eIF4E (eIF4E without bound ligands).
• To elucidate how cap structure and eIF4G binding induce folding in eIF4E.
• To characterize the kinetic interplay between eIF4E, its cap ligand, and eIF4G.

Main Methods:

• X-ray crystallography to determine structures of eIF4E in various states.
• Kinetic assays to measure binding rates and affinities.
• Site-directed mutagenesis to probe functional residues and folding pathways.

Main Results:

• Apo-eIF4E possesses extensive intrinsically disordered regions that fold upon ligand binding.
• Binding of the mRNA cap structure induces significant eIF4E folding.
• eIF4G binding also induces eIF4E folding, yielding a conformation distinct from cap-bound eIF4E.
• Interactions with binding partners modulate the kinetics of subsequent binding events.

Conclusions:

• eIF4E exists as a dynamic, adaptable protein whose structure is significantly influenced by its binding partners.
• The folding transitions of eIF4E are integral to its function in translation initiation.
• Detailed structural and kinetic data provide insights into the mechanism of mRNA recruitment.