Eukaryotic translation initiation factor 5 functions as a GTPase-activating protein

Area of Science:

• Molecular Biology
• Protein Synthesis
• Enzymology

Background:

• Eukaryotic translation initiation factor 5 (eIF5) interacts with eIF2, facilitating GTP hydrolysis on the 40S initiation complex.
• This GTPase-activating protein (GAP) function is crucial for the regulation of protein synthesis initiation.

Purpose of the Study:

• To elucidate the specific regions and residues of eIF5 essential for its GTPase-activating protein activity.
• To investigate the role of the N-terminal region and key residues in eIF5 function in vitro and in vivo.

Main Methods:

• Site-directed mutagenesis of eIF5, focusing on the N-terminal region and specific residues (Arg-15, Lys-33, Lys-55).
• Assays for GTP hydrolysis on the 40S initiation complex.
• Assessment of protein synthesis and cell growth in a yeast model (Delta TIF5 strain).

Main Results:

• The N-terminal region of eIF5, particularly Arg-15, is critical for GTP hydrolysis, independent of eIF2 beta binding.
• Mutations at Arg-15, Lys-33, and Lys-55 significantly impaired eIF5's ability to promote GTP hydrolysis.
• Mutant eIF5 proteins exhibited defects in overall protein synthesis and failed to support cell growth in yeast.

Conclusions:

• eIF5 functions as a GTPase-activating protein, with its N-terminal domain playing a vital role in catalysis.
• Specific residues, including Arg-15, Lys-33, and Lys-55, are essential for eIF5's catalytic activity and biological function.
• These findings provide insights into the mechanism of translation initiation regulation by eIF5 and other GAPs.