The ribosome modulates the structural dynamics of the conserved GTPase HflX and triggers tight nucleotide binding

► HflX tightly binds to the 70S ribosome as well as the 50S and 30S subunit. ► Ribosome interaction increases affinity for GTP binding up to 70 000-fold. ► HflX·GTP exists in a structurally distinct 50S- and 70S-bound form. ► Only 50S subunit and 70S ribosome induce tight nucleotide binding. ► HflX will mainly exist in the HflX·GTP·ribosome-bound form in vivo.