Eukaryotic translation initiation factor 5A (EIF5A) is a highly conserved protein that plays a crucial role in the translation elongation and termination phases of protein synthesis. It is the only known protein to contain the unusual post‑translational modification hypusine, which is essential for its activity.
Gene and Protein
- Gene: EIF5A is encoded by the EIF5A gene in humans, located on chromosome 17p13.1. Orthologous genes are present in a wide range of eukaryotes, including yeast, plants, and mammals.
- Protein: The mature human EIF5A protein consists of 154 amino acids (approximately 17 kDa). The distinctive hypusine residue is formed at Lysine 50 through a two‑step enzymatic process involving deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase (DOHH).
Structure
- EIF5A adopts a compact β‑sheet-rich fold known as the α/β‑barrel. The hypusine-modified lysine projects from the surface and is critical for binding to the ribosome and to RNA.
- Crystal structures of EIF5A bound to the ribosome have revealed direct contacts with the peptidyl‑tRNA substrate, suggesting a mechanistic role in facilitating peptide bond formation and translocation.
Biological Function
- Translation Elongation: EIF5A promotes the synthesis of proteins containing consecutive proline residues (poly‑proline motifs) and other peptide sequences that stall ribosomes, thereby enhancing translational efficiency.
- mRNA Turnover: It participates in the regulation of specific mRNA decay pathways, although the precise mechanisms remain under investigation.
- Cellular Proliferation: EIF5A activity is linked to cell cycle progression, especially during the G1/S transition, due to its influence on the translation of cyclins and other growth‑related proteins.
Cellular Localization
- Primarily cytoplasmic, but a fraction of EIF5A shuttles to the nucleus where it may influence nucleocytoplasmic transport and RNA metabolism.
Clinical Significance
- Cancer: Overexpression of EIF5A and its hypusination enzymes (DHS, DOHH) has been observed in several malignancies, including colorectal, pancreatic, and breast cancers. Inhibitors targeting hypusination (e.g., GC7, a DHS inhibitor) are under pre‑clinical evaluation as potential anti‑cancer agents.
- Viral Infection: Certain viruses exploit EIF5A for efficient production of viral proteins; modulation of EIF5A activity can affect viral replication cycles.
- Genetic Disorders: Mutations affecting the hypusination pathway have been associated with developmental defects and neurodevelopmental disorders, though such cases are rare.
Therapeutic Targeting
- Hypusination Inhibitors: Small‑molecule inhibitors of DHS and DOHH are being explored to reduce EIF5A activity in tumor cells.
- RNAi and CRISPR Approaches: Gene‑silencing strategies targeting EIF5A expression have demonstrated reduced tumor growth in experimental models.
Interactions
- EIF5A interacts with ribosomal proteins (e.g., RPL5, RPL11), translation elongation factors, and components of the eukaryotic initiation complex. It also binds to specific mRNA motifs that influence translation elongation rates.
Evolutionary Conservation
- The presence of EIF5A and the hypusine modification is conserved from yeast (Saccharomyces cerevisiae) to humans, underscoring its fundamental role in cellular biology.
References
- Park, M. H., & Wolff, G. (2018). The role of eIF5A in translation elongation. Trends in Biochemical Sciences, 43(7), 527‑540.
- van den Heuvel, S., & Schmitt, M. E. (2014). Hypusine biosynthesis and function. Biochemical Journal, 459(3), 329‑340.
- Li, J., et al. (2021). Targeting eIF5A hypusination as a therapeutic strategy in cancer. Cancer Research, 81(13), 3501‑3513.
