During protein synthesis, tRNAs move from the ribosome’s aminoacyl to peptidyl to exit sites. We caracterize conformational motions during spontaneous translocation, using molecular dynamics simulations of 13 intermediate-translocation-state models obtained by combining <i>Escherichia coli</i> ribosome crystal structures with cryo-EM data. Resolving fast transitions between states, we find that tRNA motions govern the transition rates within the pre- and post-translocation states. Intersubunit rotations and L1-stalk motion exhibit fast intrinsic submicrosecond dynamics. The L1 stalk drives the tRNA from the peptidyl site and links intersubunit rotation to translocation. Displacement of tRNAs is controlled by ‘sliding’ and ‘stepping’ mechanisms involving conserved L16, L5 and L1 residues, thus ensuring binding to the ribosome despite large-scale tRNA movement. A very dynamic network of inter-subunit contacts fine-tunes the affinity between the 30S and 50S subunits, thus facilitating fast translation.

Energy barriers and driving forces in tRNA translocation through the ribosome

249th National Meeting (2015)

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