Interface of the interaction of the middle domain of human translation termination factor eRF1 with eukaryotic ribosomes

Translation termination in eukaryotes is governed by the interaction of two, class 1 and class 2, polypeptide chain release factors with the ribosome. The middle (M) domain of the class 1 factor eRF1 contains the strictly conserved GGQ motif and is involved in hydrolysis of the peptidyl-tRNA ester bond in the peptidyl transferase center of the large ribosome subunit. Heteronuclear NMR spectroscopy was used to map the interaction interface of the M domain of human eRF1 with eukaryotic ribosomes. The protein was found to specifically interact with the 60S subunit, since no interaction was detected with the 40S subunit. The amino acid residues forming the interface mostly belong to long helix alpha 1 of the M domain. Some residues adjacent to alpha 1 and belonging to strand beta 5 and short helices alpha 2 and alpha 3 are also involved in the protein-ribosome contact. The functionally inactive G183A mutant interacted with the ribosome far more weakly as compared with the wild-type eRF1. The interaction interfaces of the two proteins were nonidentical. It was concluded that long helix alpha 1 is functionally important and that the conformational flexibility of the GGQ loop is essential for the tight protein-ribosome contact.