Structural insights into cognate versus near-cognate discrimination during decoding.

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• The ribosome facilitates accurate protein synthesis by selecting the correct transfer RNA (tRNA).
• Understanding the mechanism of tRNA selection is crucial for deciphering translational fidelity.

Purpose of the Study:

• To investigate the structural basis of tRNA selection by the ribosome.
• To characterize the interaction of near-cognate tRNA with elongation factor Tu (EF-Tu) and the ribosome.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to visualize ribosome-ternary complex (TC) interactions.
• Image classification and 3D reconstruction were employed to analyze over 350,000 images.
• Structural analysis focused on the arrangement of near-cognate Trp-tRNA(Trp) with EF-Tu and the ribosome.

Main Results:

• Approximately 8% of TCs were found bound to the ribosome programmed with UGA codons.
• The near-cognate tRNA's acceptor stem region exhibited flexibility, with a disordered CCA end.
• Structural differences were observed compared to the cognate tRNA interaction (UGG codon).

Conclusions:

• The study provides direct structural insights into the ribosome's induced-fit decoding mechanism.
• Analysis of interactions reveals how conformational signals differ between cognate and near-cognate tRNA binding.
• This work elucidates key aspects of translational accuracy at a molecular level.