Common chaperone activity in the G-domain of trGTPase protects L11-L12 interaction on the ribosome.

Translational GTPases (trGTPases) regulate all phases of protein synthesis. An early event in the interaction of a trGTPase with the ribosome is the contact of the G-domain with the C-terminal domain (CTD) of ribosomal protein L12 (L12-CTD) and subsequently interacts with the N-terminal domain of L11 (L11-NTD). However, the structural and functional relationships between L12-CTD and L11-NTD remain unclear. Here, we performed mutagenesis, biochemical and structural studies to identify the interactions between L11-NTD and L12-CTD. Mutagenesis of conserved residues in the interaction site revealed their role in the docking of trGTPases. During docking, loop62 of L11-NTD protrudes into a cleft in L12-CTD, leading to an open conformation of this domain and exposure of hydrophobic core. This unfavorable situation for L12-CTD stability is resolved by a chaperone-like activity of the contacting G-domain. Our results suggest that all trGTPases-regardless of their different specific functions-use a common mechanism for stabilizing the L11-NTD•L12-CTD interactions.