Abstract
Contrary to the widely held belief that mitochondrial ribosomes (mitoribosomes) are highly similar to bacterial ones, recent experimental evidence reveals that mitoribosomes do differ significantly from their bacterial counterparts. This review is focused on plant mitoribosomes, but we also highlight the most striking similarities and differences between the plant and non-plant mitoribosomes. An analysis of the composition and structure of mitoribosomes in trypanosomes, yeast, mammals and plants uncovers numerous organism-specific features. For the plant mitoribosome, the most striking feature is the enormous size of the small subunit compared to the large one. Apart from the new structural information, possible functional peculiarities of different types of mitoribosomes are also discussed. Studies suggest that the protein composition of mitoribosomes is dynamic, especially during development, giving rise to a heterogeneous populations of ribosomes fulfilling specific functions. Moreover, convincing data shows that mitoribosomes interact with components involved in diverse mitochondrial gene expression steps, forming large expressosome-like structures.
Highlights
The endosymbiotic theory maintains that mitochondria evolved by the engulfment of an alpha-proteobacterium by a eukaryotic progenitor cell [1]
Mitoribosomes are responsible for the translation of the essential mitochondrial mRNAs, such as those coding for components of oxidative phosphorylation (OXPHOS) complexes
In papers from our laboratory [46,49,50] we have shown that the alteration in mitoribosomal protein composition caused by gene silencing can affect the functioning of the mitoribosome
Summary
The endosymbiotic theory maintains that mitochondria evolved by the engulfment of an alpha-proteobacterium by a eukaryotic progenitor cell [1]. The LSU contains the peptidyl transferase center (PTC) which catalyzes the formation of peptide bonds linking the amino acids delivered by the tRNAs into a polypeptide chain. Both mitoribosomal subunits consist of mitoribosomal RNAs (mtrRNAs) and mitoribosomal proteins (mtRPs) encoded, respectively, by the mitochondrial and mostly by the nuclear genome. Mitoribosomes are quite divergent from the bacterial ribosome and vary significantly between different species [5,6,7,8,9,10,11,12] This very dynamic evolutionary history of the mitoribosome indicates its uniqueness, since bacterial, cytosolic, and chloroplast ribosomes are much more uniform in terms of their rRNA and protein composition [2]. The Plant Mitoribosome Is Structurally and Compositionally Distinct from both Prokaryotic and Non-Plant Mitochondrial Ribosomes
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