Mitochondria secrets exposed
Cryo-EM: Ribosomes imaged on the surface of mitochondria [University of Exeter].
Using cryo-electron microscopy, researchers at the University of Exeter, UK, have imaged the mitochondrial protein production process.
Latest analyses reveal that some ribosomes - tiny protein-making factories - are attached to mitochondria inside a cell.
These ribosomes push proteins across the double membrane-bound mitochondria, and into the organelle.
The discoveries open new avenues for studying protein targeting and mitochondrial dysfunction, which has been implicated in diseases including cancer and neurodegenerative disorders such as Parkinson’s.
“Proteins are responsible for nearly all cellular processes," highlights Dr Vicki Gold from the Living Systems Institute at the University of Exeter. "The cell has to make a huge variety of proteins and target them to the precise location where they are needed to function.”
“In the case of mitochondria, proteins have to cross the boundary of two membranes to get inside them," she adds. "We looked for - and were able to image at unprecedented detail - ribosomes attached to mitochondria.”
To visualise the so-called cytosolic ribosomes, Gold and colleagues carried out electron cryo-tomography on frozen mitochondrial samples, using either a Tecnai Polara, Titan Krios, or JEM‐3200FSC.
Each instrument was equipped with field emission guns operating at 300 keV, K2 Summit direct electron detector cameras and a post‐column Quantum energy filter operated at a slit width of 20 eV or an in‐column energy filter operated with a slit width of 40 eV.
The ribosomes were shown to interact with the 'TOM' complex, a complex of proteins found in the outer mitochondrial membrane of the mitochondria
According to the researchers, nascent chain building was crucial for ribosome recruitment and stabilisation.
As Gold highlights: "Ribosomes are bound to the membrane in discrete clusters... and this interaction highlights how protein synthesis may be coupled with transport."
"Our work provides unique insights into the spatial organization of cytosolic ribosomes on mitochondria," she adds.
Research is published in EMBO Reports.