Nucleotide modifications and tRNA anticodon-mRNA codon interactions on the ribosome

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Transfer RNA (tRNA) modifications are crucial for accurate protein synthesis.
• Specific modifications like 5-methoxyuridine (cmo(5)U34) and N6-adenosine methylation (m(6)A37) at the tRNA anticodon loop are known to influence codon recognition.
• The precise atomic-level mechanisms behind the expanded decoding capabilities conferred by these modifications remain largely unknown.

Purpose of the Study:

• To elucidate the atomic-level mechanisms by which tRNA modifications cmo(5)U34 and m(6)A37 enhance codon decoding at the ribosome.
• To quantify the effects of these modifications on tRNA-mRNA-ribosome interactions.
• To investigate the role of entropic effects in the extended reading capabilities.

Main Methods:

• Molecular dynamics (MD) simulations of tRNA anticodon and mRNA codon interactions within the ribosome.
• Free energy perturbation (FEP) calculations coupled with umbrella sampling.
• Entropy calculations for tRNA in both free and ribosome-bound states.
• Detailed structural analysis of the ribosomal decoding center.

Main Results:

• No significant prestructuring effect of cmo(5)U34 and m(6)A37 on the tRNA anticodon stem-loop was observed.
• Two key mechanisms contributing to expanded decoding were identified: 1) cmo(5)U34 facilitates alternative outer conformations for non-cognate base pairs, and 2) these modifications increase favorable contacts between tRNA, mRNA, and the ribosome.
• Quantification of entropic contributions to decoding was performed.

Conclusions:

• The expanded decoding capabilities of tRNA(Val) by modifications cmo(5)U34 and m(6)A37 are primarily driven by altered conformational flexibility and enhanced molecular interactions, rather than prestructuring.
• These findings provide atomic-level insights into the molecular basis of translational fidelity and adaptability.
• The study highlights the significant role of post-transcriptional modifications in fine-tuning the decoding process within the ribosome.