Structural Insights into the Mechanism of Mitoribosomal Large Subunit Biogenesis

Mol Cell. 2020 Aug 20;79(4):629-644.e4. doi: 10.1016/j.molcel.2020.06.030. Epub 2020 Jul 16.


In contrast to the bacterial translation machinery, mitoribosomes and mitochondrial translation factors are highly divergent in terms of composition and architecture. There is increasing evidence that the biogenesis of mitoribosomes is an intricate pathway, involving many assembly factors. To better understand this process, we investigated native assembly intermediates of the mitoribosomal large subunit from the human parasite Trypanosoma brucei using cryo-electron microscopy. We identify 28 assembly factors, 6 of which are homologous to bacterial and eukaryotic ribosome assembly factors. They interact with the partially folded rRNA by specifically recognizing functionally important regions such as the peptidyltransferase center. The architectural and compositional comparison of the assembly intermediates indicates a stepwise modular assembly process, during which the rRNA folds toward its mature state. During the process, several conserved GTPases and a helicase form highly intertwined interaction networks that stabilize distinct assembly intermediates. The presented structures provide general insights into mitoribosomal maturation.

Keywords: Trypanosoma brucei; assembly factors; cryo-EM structure; mitochondrial ribosome; mitoribosome; peptidyltransferase center; ribosomal GTPases; ribosomal maturation; ribosome assembly; ribosome biogenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cryoelectron Microscopy
  • DEAD-box RNA Helicases / chemistry
  • DEAD-box RNA Helicases / metabolism
  • GTP Phosphohydrolases / chemistry
  • GTP Phosphohydrolases / genetics
  • GTP Phosphohydrolases / metabolism
  • Mitochondrial Ribosomes / chemistry*
  • Mitochondrial Ribosomes / metabolism
  • Models, Molecular
  • Nucleic Acid Conformation
  • RNA, Ribosomal / chemistry
  • RNA, Ribosomal / metabolism*
  • Ribosomal Proteins / chemistry
  • Ribosomal Proteins / genetics
  • Ribosomal Proteins / metabolism
  • Ribosome Subunits, Large / chemistry*
  • Ribosome Subunits, Large / metabolism
  • Trypanosoma brucei brucei / genetics
  • Trypanosoma brucei brucei / metabolism*


  • RNA, Ribosomal
  • RNA, ribosomal, 12S
  • Ribosomal Proteins
  • GTP Phosphohydrolases
  • DEAD-box RNA Helicases