Numerous rRNA molecules form the apicomplexan mitoribosome via repurposed protein and RNA elements

Area of Science:

• Molecular Biology
• Parasitology
• Structural Biology

Background:

• Mitochondrial ribosomes (mitoribosomes) synthesize essential mitochondrial proteins.
• Typically, mitoribosomes comprise a few long, self-folding rRNA molecules.
• Apicomplexan parasites like Toxoplasma gondii possess unusually structured mitoribosomes.

Purpose of the Study:

• To elucidate the structural features enabling the function of the Toxoplasma gondii mitoribosome.
• To investigate the role of poly-A tails in mitoribosome assembly and function.
• To understand mechanisms behind extreme mitochondrial genome reduction in Apicomplexa.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to determine the structure.
• Functional assays were performed to assess the essentiality of poly-A tails.
• Comparative genomics and structural analysis were used to identify conserved and novel features.

Main Results:

• T. gondii mitoribosomes assemble from over 50 short rRNA molecules.
• Poly-A tails are integrated into the mitoribosome structure, crucial for its formation and parasite survival.
• Nine rRNA sequences are duplicated, contributing to mitochondrial genome reduction.
• Repurposed transcription factors, including ApiAP2 family members, compensate for lost ribosomal domains.

Conclusions:

• The Toxoplasma gondii mitoribosome exhibits a unique architecture with integrated poly-A tails, essential for its function.
• This structure provides insights into extreme mitochondrial genome reduction in Apicomplexa.
• Repurposing of transcription factors highlights adaptive strategies in microbial eukaryotes.