Structural basis for the enhancement of eIF4A helicase activity by eIF4G

Area of Science:

• Molecular Biology
• Protein Biochemistry
• Structural Biology

Background:

• Eukaryotic translation initiation factors 4A (eIF4A) and 4G (eIF4G) are essential for ribosome assembly and mRNA recruitment.
• eIF4A, an RNA helicase, exhibits low activity alone but is stimulated by eIF4G.

Purpose of the Study:

• To elucidate the specific interaction interface between eIF4A and the middle domain of eIF4G (eIF4G-m).
• To understand how this interaction contributes to the regulation of eIF4A activity within the eIF4F complex.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy was employed to define the binding site.
• Site-directed mutagenesis was used to confirm the identified interface residues.

Main Results:

• The primary interaction surface between eIF4A and eIF4G-m is located on the C-terminal domain of eIF4A.
• This interface is adjacent to regions involved in binding RNA, ATP, and the N-terminal domain of eIF4A (eIF4A-NTD).
• Mutations at the interface disrupted binding and confirmed the interaction, revealing that the N-terminal end of eIF4G-m binds the C-terminal domain of eIF4A.

Conclusions:

• eIF4G-m acts as a soft clamp, stabilizing a closed conformation of eIF4A.
• This stabilization mechanism explains the cooperativity of eIF4A with its binding partners (eIF4G, RNA, ATP) and the stimulation of its helicase activity in the eIF4F complex.