Ribosome dynamics and tRNA movement by time-resolved electron cryomicroscopy

Area of Science:

• Molecular Biology
• Structural Biology
• Biophysics

Background:

• Protein synthesis involves complex ribosome-transfer RNA (tRNA) rearrangements during translocation.
• Understanding tRNA dynamics within the ribosome is crucial for deciphering gene expression mechanisms.

Purpose of the Study:

• To visualize and characterize the movement of tRNA through the ribosome during translocation.
• To elucidate the conformational changes and dynamic interactions governing tRNA translocation.

Main Methods:

• Time-resolved single-particle electron cryomicroscopy (cryo-EM) was employed to capture snapshots of tRNA within the ribosome.
• Unbiased computational sorting of cryo-EM images enabled the reconstruction of 50 distinct intermediate states.

Main Results:

• Detailed 3D reconstructions revealed tRNAs in classical, hybrid, and novel intermediate states, mapping their trajectories.
• Coupling of tRNA movement with ribosomal subunit conformational changes, particularly the small subunit head and body, was observed.
• Dynamic interactions between tRNAs and ribosomal residues were shown to dictate the tRNA path.

Conclusions:

• The ribosome functions as a Brownian machine, utilizing thermal energy for directed tRNA movement.
• A surprisingly flat energy landscape for conformational variations was observed at physiological temperatures.
• This work provides kinetic information and insights into the mechanics of tRNA translocation.