Ribosome-bound eukaryotic elongation factor 2 protects 5 S rRNA from modification

Area of Science:

• Molecular Biology
• Ribosome Function
• Protein Synthesis

Background:

• The 80S ribosome is central to eukaryotic protein synthesis.
• Eukaryotic elongation factor 2 (eEF-2) mediates polypeptide chain elongation.
• Understanding eEF-2's interaction with ribosomes is crucial for deciphering translational regulation.

Purpose of the Study:

• To investigate the structural changes in 5S ribosomal RNA (rRNA) upon eEF-2 binding.
• To determine the accessibility of 5S rRNA within reconstituted 80S ribosomes.
• To elucidate the role of ribosome conformation in eEF-2-mediated regulation.

Main Methods:

• Reconstitution of 80S ribosomes from subunits.
• Chemical and enzymatic modification of 5S rRNA.
• Primer extension analysis using a 5S rRNA-specific probe.
• Treatment with ricin to induce post-translocation state.
• Binding of eEF-2 with GTP analogue (GMPPCP).

Main Results:

• Reactive sites on 5S rRNA were mapped between nucleotides 38-99, primarily in single-stranded regions.
• Ricin treatment exposed additional bases, indicating increased 5S rRNA accessibility in the post-translocation state.
• eEF-2 binding, in complex with GMPPCP, protected most exposed 5S rRNA bases from modification.

Conclusions:

• Ribosome conformation influences 5S rRNA accessibility.
• eEF-2 binding induces a conformational change that shields 5S rRNA.
• This protection mechanism may play a role in regulating translation by modulating ribosome structure.