Structure of the mature kinetoplastids mitoribosome and insights into its large subunit biogenesis

Area of Science:

• Molecular Biology
• Parasitology
• Structural Biology

Background:

• Kinetoplastids are unicellular eukaryotes causing diseases like Chagas disease and leishmaniasis.
• Their single large mitochondrion contains specialized molecular machinery, including unique mitochondrial ribosomes (mitoribosomes).
• Previous studies focused on the small subunit of mitoribosomes, leaving the large subunit (LSU) structure and maturation poorly understood.

Purpose of the Study:

• To elucidate the structure of the large subunit (LSU) of kinetoplastid mitoribosomes.
• To identify ribosomal proteins and RNA components of the LSU.
• To characterize the LSU assembly intermediates and the roles of maturation factors.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structures.
• Analysis of mitoribosomes from *Leishmania tarentolae* and *Trypanosoma cruzi*.
• Identification of ribosomal proteins, rRNA, and associated maturation factors.

Main Results:

• The complete structure of mature mitoribosomes from *L. tarentolae* and *T. cruzi* was determined.
• The complete LSU rRNA and previously unidentified ribosomal proteins were identified.
• The structure of an LSU assembly intermediate, involving 16 maturation factors, was revealed.
• Maturation factors were shown to act on both sides of the LSU, refolding and modifying rRNA, and preventing premature translation.

Conclusions:

• This study provides unprecedented structural insights into kinetoplastid mitoribosome LSU biogenesis.
• Identified maturation factors are essential for proper LSU assembly, rRNA processing, and ensuring translation only occurs after full maturation.
• The findings contribute to understanding parasite biology and potential therapeutic targets.