EMD-13660
Middle assembly intermediate of the Trypanosoma brucei mitoribosomal small subunit
EMD-13660
Single-particle3.6 Å
Deposition: 29/09/2021
Map released: 02/03/2022
Last modified: 13/11/2024
Sample Organism:
Trypanosoma brucei brucei
Sample: Middle assembly intermediate of the Trypanosoma brucei mitoribosomal small subunit
Fitted models: 7pua (Avg. Q-score: 0.436)
Deposition Authors: Lenarcic T, Leibundgut M
Sample: Middle assembly intermediate of the Trypanosoma brucei mitoribosomal small subunit
Fitted models: 7pua (Avg. Q-score: 0.436)
Deposition Authors: Lenarcic T, Leibundgut M
Mitoribosomal small subunit maturation involves formation of initiation-like complexes.
Lenarcic T,
Niemann M,
Ramrath DJF,
Calderaro S,
Flugel T,
Saurer M ,
Leibundgut M,
Boehringer D ,
Prange C ,
Horn EK,
Schneider A ,
Ban N
(2022) PNAS , 119
(2022) PNAS , 119
Abstract:
Mitochondrial ribosomes (mitoribosomes) play a central role in synthesizing mitochondrial inner membrane proteins responsible for oxidative phosphorylation. Although mitoribosomes from different organisms exhibit considerable structural variations, recent insights into mitoribosome assembly suggest that mitoribosome maturation follows common principles and involves a number of conserved assembly factors. To investigate the steps involved in the assembly of the mitoribosomal small subunit (mt-SSU) we determined the cryoelectron microscopy structures of middle and late assembly intermediates of the Trypanosoma brucei mitochondrial small subunit (mt-SSU) at 3.6- and 3.7-Å resolution, respectively. We identified five additional assembly factors that together with the mitochondrial initiation factor 2 (mt-IF-2) specifically interact with functionally important regions of the rRNA, including the decoding center, thereby preventing premature mRNA or large subunit binding. Structural comparison of assembly intermediates with mature mt-SSU combined with RNAi experiments suggests a noncanonical role of mt-IF-2 and a stepwise assembly process, where modular exchange of ribosomal proteins and assembly factors together with mt-IF-2 ensure proper 9S rRNA folding and protein maturation during the final steps of assembly.
Mitochondrial ribosomes (mitoribosomes) play a central role in synthesizing mitochondrial inner membrane proteins responsible for oxidative phosphorylation. Although mitoribosomes from different organisms exhibit considerable structural variations, recent insights into mitoribosome assembly suggest that mitoribosome maturation follows common principles and involves a number of conserved assembly factors. To investigate the steps involved in the assembly of the mitoribosomal small subunit (mt-SSU) we determined the cryoelectron microscopy structures of middle and late assembly intermediates of the Trypanosoma brucei mitochondrial small subunit (mt-SSU) at 3.6- and 3.7-Å resolution, respectively. We identified five additional assembly factors that together with the mitochondrial initiation factor 2 (mt-IF-2) specifically interact with functionally important regions of the rRNA, including the decoding center, thereby preventing premature mRNA or large subunit binding. Structural comparison of assembly intermediates with mature mt-SSU combined with RNAi experiments suggests a noncanonical role of mt-IF-2 and a stepwise assembly process, where modular exchange of ribosomal proteins and assembly factors together with mt-IF-2 ensure proper 9S rRNA folding and protein maturation during the final steps of assembly.