X-ray crystallography study on ribosome recycling: the mechanism of binding and action of RRF on the 50S ribosomal subunit

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Abstract
This study presents the crystal structure of domain I of the Escherichia coli ribosome recycling factor (RRF) bound to the Deinococcus radiodurans 50S subunit. The orientation of RRF is consistent with the position determined on a 70S‐RRF complex by cryoelectron microscopy (cryo‐EM). Alignment, however, requires a rotation of 7° and a shift of the cryo‐EM RRF by a complete turn of an α‐helix, redefining the contacts established with ribosomal components. At 3.3 Å resolution, RRF is seen to interact exclusively with ribosomal elements associated with tRNA binding and/or translocation. Furthermore, these results now provide a high‐resolution structural description of the conformational changes that were suspected to occur on the 70S‐RRF complex, which has implications for the synergistic action of RRF with elongation factor G (EF‐G). Specifically, the tip of the universal bridge element H69 is shifted by 20 Å toward h44 of the 30S subunit, suggesting that RRF primes the intersubunit bridge B2a for the action of EF‐G. Collectively, our data enable a model to be proposed for the dual action of EF‐G and RRF during ribosome recycling.