The translation initiation factor EIF4E5 from Leishmania: crystal structure and interacting partners.

Area of Science:

• Molecular Biology
• Parasitology
• Structural Biology

Background:

• Eukaryotic translation initiation is regulated by the mRNA cap-binding protein eIF4E and its associated factors.
• Pathogenic trypanosomatids possess multiple eIF4E and eIF4G proteins with incompletely understood roles.
• The eIF4E5 protein in Leishmania species remains largely uncharacterized.

Purpose of the Study:

• To identify and characterize the interacting partners of eIF4E5 in *Leishmania infantum*.
• To elucidate the structural and functional differences of *Leishmania* eIF4E5 compared to its orthologs.
• To investigate the role of eIF4E5 in parasite translation regulation.

Main Methods:

• Immunoprecipitation assays coupled with mass-spectrometry to identify protein interactions.
• Site-directed mutagenesis to assess the role of specific tryptophan residues.
• X-ray crystallography to determine the 3D structure of *Leishmania* eIF4E5.

Main Results:

• *Leishmania* eIF4E5 primarily interacts with eIF4G1, eIF4G1-IP, RBP43, and 14-3-3 proteins, but not eIF4G2.
• Interactions with protein kinases, RNA-binding proteins, and histones were also observed.
• Mutagenesis of key tryptophan residues did not significantly alter identified interactions.
• Structural analysis revealed significant differences in the eIF4G binding interface and C-terminal region compared to human and *Trypanosoma* eIF4E5.
• Phosphorylated residues were identified at the C-terminal end.

Conclusions:

• *Leishmania* eIF4E5 forms distinct complexes, suggesting specialized roles in translation initiation.
• Structural variations imply unique cap-binding and regulatory mechanisms in *Leishmania*.
• These findings provide insights into parasite-specific translation control and potential therapeutic targets.