The Findings Shed New Light on Mitoribosomes, Which Are Unique Ribosomes Located Inside the Mitochondria of Cells

The tiny protein-producing factories known as ribosomes are present in every cell and have a remarkably similar appearance throughout the entire tree of life.

In terms of structure, those that keep bacteria alive are very similar to the ribosomes that produce proteins in our human cells.

How a cell's mitochondria make their protein factories

(Photo : LOIC VENANCE/AFP via Getty Images)

The RNA and protein components of their mitoribosomes, however, can differ significantly between two organisms, even those with similar ribosomes, as per ScienceDaily.

Mitoribosomes, specialized ribosomes found in the mitochondria (the energy-producing organelles in our cells), assist the mitochondria in making the proteins needed to make ATP, the cell's primary source of energy.

Sebastian Klinge's lab was home to researchers who were curious about the evolution of mitoribosomes, how they come together within cells, and why their structures vary so greatly between species.

They produced 3D images of the small components of yeast and human mitoribosomes during assembly to provide answers to these questions.

Their research, which was published in Nature, illuminated the fundamentals of mitoribosome construction and may have relevance for the treatment of rare diseases associated with damaged mitoribosomes.

The team was able to directly observe many similarities and differences in mitoribosome assembly between two different species, yeast, and humans.

One significant difference was that various proteins were frequently involved in otherwise comparable acts of RNA folding.

According to Harper, this is most likely because "there are common obstacles for these ribosomes." You couldn't compare it to producing two different types of bikes, a road bike, and a mountain bike.

For each, you might need additional components or equipment, but some crucial production steps will be the same.

The findings offer novel explanations for how molecular complexity and diversity develop in macromolecular complexes as well as how assembly systems change over time.

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Technologies That Allowed to Identify Mitoribosome-Specific Proteins

Only five years after the first description of ribosomes, it was hypothesized in the late 1950s that complexes capable of protein synthesis would be present in mitochondria, as per MDPI.

These early reports described the sedimentation coefficient and the likely rRNA content of these mitoribosomes, already linking them to bacteria.

The two-dimensional polyacrylamide gel electrophoresis (PAGE) analysis of purified bovine mitoribosomes, which revealed that these mitoribosomes would be composed of more than 80 proteins, therefore more than found in bacteria, but without knowing exactly their nature, would also not provide clarity on their protein composition until more than 10 years later.

Early in the 2000s, the putative protein composition of the small and large subunits of the mammalian mitoribosome was first characterized thanks to the development of protein sequencing and mass spectrometry in the 1990s.

These studies have already demonstrated the existence of conserved bacterial homologs and their absence, as well as putative proteins that may share mitoribosomes with yeast and some that are unique to animals.

Their function within the ribosome was unknown, though.

A mitoribosome's first cryo-EM characterization was published in 2003.

The bovine mitoribosome's architecture was described in this study at a resolution of about 10, which is insufficient to clearly identify the r-proteins that are unique to the mitoribosome.

It did, however, support the mitoribosome's largely proteic nature and distinct appearance from bacterial and cytosolic ribosomes.

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