Dynamics and Regulation of mRNA Cap Recognition by Human eIF4F.

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Eukaryotic translation initiation is crucial for gene expression and tightly regulated by the initiation factor 4F (eIF4F) complex.
• The eIF4F complex (eIF4E, eIF4G, and eIF4A) binds the mRNA 5' cap, facilitating ribosome recruitment.
• The precise dynamics of human eIF4F-mRNA interactions remain poorly understood, limiting mechanistic insights into translation regulation.

Purpose of the Study:

• To investigate the dynamic interactions within the human eIF4F complex during mRNA cap recognition.
• To elucidate the roles of individual eIF4F subunits in regulating translation initiation.
• To understand the mechanistic basis of cap-dependent translation regulation.

Main Methods:

• Single-molecule fluorescence assays to visualize eIF4E-mRNA cap binding in real-time.
• Biochemical assays to study subunit interactions within the eIF4F complex.
• Molecular dynamics simulations to model electrostatic interactions and binding dynamics.

Main Results:

• Human eIF4G, particularly its C-terminus, represses the transient binding of eIF4E to the mRNA cap.
• Nucleotide-bound eIF4A relieves this repression, acting as a key determinant for efficient cap recognition.
• eIF4G modulates eIF4E-mRNA interaction frequency through electrostatic interactions, revealing its role as a rate-limiting factor.
• Intrinsic eIF4F-mRNA dynamics alone are insufficient for cap-tethered ribosomal scanning.

Conclusions:

• Human eIF4G plays an unexpected, central regulatory role in controlling mRNA cap recognition by eIF4F.
• eIF4A is critical for overcoming eIF4G-mediated repression, thereby promoting efficient translation initiation.
• Significant differences exist in mRNA recognition mechanisms and subunit roles between human and yeast eIF4F complexes.
• These findings provide fundamental insights into the regulation of eukaryotic translation initiation.