Evolutionary shift toward protein-based architecture in trypanosomal mitochondrial ribosomes

Abstract

Ribosomal RNA (rRNA) plays key functional and architectural roles in ribosomes. Using electron microscopy, we determined the atomic structure of a highly divergent ribosome found in mitochondria of , a unicellular parasite that causes sleeping sickness in humans. The trypanosomal mitoribosome features the smallest rRNAs and contains more proteins than all known ribosomes. The structure shows how the proteins have taken over the role of architectural scaffold from the rRNA: They form an autonomous outer shell that surrounds the entire particle and stabilizes and positions the functionally important regions of the rRNA. Our results also reveal the "minimal" set of conserved rRNA and protein components shared by all ribosomes that help us define the most essential functional elements.

Identification of the Toxoplasma gondii mitochondrial ribosome, and characterisation of a protein essential for mitochondrial translation

“…A recent structure of the mitochondrial ribosome of Trypanosoma brucei showed an evolutionary shift towards a higher ribosome protein content rather than the RNA heavy complexes of mammalian ribosomes (Ramrath et al , ). These findings from T. brucei illustrates the importance of studying basic cellular components in a diverse array of models, however, this is not possible without detecting mitochondrial ribosomes and validating mitochondrial ribosomal proteins.…”

“…The proportion of proteins and rRNA making up mitoribosomes changes drastically among divergent organisms, and this results in variability of ribosome diameter, kilo Dalton size and number of mitoribosomal proteins (e.g. Ramrath et al , vs Greber et al , ). As expected, those parameters affect the mechanism of mitoribosomal functions, highlighting the importance of experimentally addressing these details in varying systems.…”

Cryo-EM structure of the RNA-rich plant mitochondrial ribosome

“…Mitoribosomes are in charge of translating the few essential mRNAs still encoded by mitochondrial genomes 3 . While chloroplast ribosomes strongly resemble those of bacteria 4,5 , mitoribosomes have diverged significantly during evolution and present strikingly different structures across eukaryotic species [6][7][8][9][10] . In contrast to animals and trypanosomatides, plants mitoribosomes have unusually expanded ribosomal RNAs and conserved the short 5S rRNA, which is usually missing in mitoribosomes 11 .…”

Genetic ablation of the mitochondrial ribosome inPlasmodium falciparumsensitizes the human malaria parasite to antimalarial drugs targeting mitochondrial functions

“…However, the degree of rRNA fragmentation observed in the mitoribosome of malaria parasites greatly surpasses these examples. Recent groundbreaking advancements in cryo-EM technology have resolved the structures of mitoribosomes from yeast (27,28), mammals (29)(30)(31)(32)(33)(34) and Trypanosoma brucei (a protist) (35). These studies have greatly increased our understanding of mitoribosomes and interactions of rRNA and ribosomal proteins (rProteins).…”