Fig. 6: A structural view of the on-ribosome eIF5B catalysis.
After Met-tRNAiMet (green) is delivered to the P site of the small subunit (40S, yellow) and the start codon is recognized, eIF5B in its GTP-bound form is able to transiently stabilize the aminoacyl-tRNA in the P site and catalyze the recruitment of the large subunit (60S, blue). Proper positioning of Met-tRNAiMet, eIF5B, and the 60S would lead to the structuring of the uL16 loop (residues 100–120) which in turn anchors eIF5B DIV solidly to the 60S in the vicinity of the PTC. The successful establishment of these interactions signals for eIF5B GTPase activation and GTP hydrolysis, which happens in the G domain of eIF5B placed near the GTPase activation center of the 60S. GTP hydrolysis by eIF5B is followed by the de-structuring of switch I, which reduces the affinity of the factor to the ribosome. The final departure of eIF5B from the ribosome is likely implemented in two steps, beginning with the super-domain G/II and followed by the detachment of DIV-h12-DIII.
