Nutritional stress affects an atypical cap-binding protein in Leishmania

Alexandra Zinoviev, Shachar Manor, Michal Shapira

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


Many eukaryotes encode multiple isoforms of the cap-binding translation initiation factor (eIF4E). Leishmanias and other trypanosomatids encode four paralogs of this protein, but none can complement the eIF4E function in a yeast mutant. A low conservation is observed between the four paralogs, suggesting they assist these organisms survive a multitude of conditions encountered throughout the life cycle. Earlier attempts to decipher their function led to identification of LeishIF4E-4 as the canonical translation initiation factor. LeishIF4E-1 appears to function during thermal stress, via a mechanism not yet understood. LeishIF4E-3 hardly binds cap-4 and is, therefore, less likely to serve as a typical initiation factor. Although it interacts with an eIF4G homolog, LeishIF4G-4, the two polypeptides do not co-migrate on sucrose gradients. While LeishIF4E-3 enters large particles that increase in size during nutritional stress, LeishIF4G-4 is found only in the top fractions. Confocal microscopy localized LeishIF4E-3 (but not LeishIF4G-4) within nutritional stress-induced granules. Accordingly, interaction between the two proteins reduced upon starvation. We therefore propose that under normal conditions, LeishIF4G-4 sequesters LeishIF4E-3 in the cytoplasm. During a nutritional stress, LeishIF4E-3 is modified and released from LeishIF4G-4 to enter stress granules, where inactive mRNAs are stored. Binding of LeishIF4G-4 to LeishIF4E-3 requires a short peptide within the LeishIF4G-4 N-terminus, which bears no similarity to the consensus 4E-binding peptide, YXXXXLφ. Mutational analysis combined with structure prediction indicates that this interaction is based on an obligatory, conserved á helix in LeishIF4G-4. These features further highlight the uniqueness of LeishIF4E-3 and how it interacts with its binding partners.

Original languageEnglish
Pages (from-to)1450-1460
Number of pages11
JournalRNA Biology
Issue number12
StatePublished - 1 Jan 2012


  • 4E-binding peptide
  • Leishmania
  • RNA granules
  • eIF4E
  • eIF4G

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology


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