Uncovering Novel Aspects of Mitochondrial Translation

In a recent WCMR Science Seminar, we heard from Dr Matt Zorkau about his research project that involves investigating novel aspects of mitochondrial translation. Read on to find out more.

Eukaryotic cells contain two genomes: one in the nucleus and the multicopy mitochondrial genome (mtDNA) distributed throughout the dynamic mitochondrial network. Human mtDNA encodes 13 essential protein components of the oxidative phosphorylation machinery that cells utilise to generate ATP. The translation of these proteins is a crucial factor in maintaining both the biogenesis and function of mitochondria for maintaining cellular homeostasis.

Work characterising mitochondrial translation has previously focussed on the various accessory proteins involved, mitochondrial ribosome structure and biochemically dissecting assembly pathways of the mitochondrial-encoded proteins into OXPHOS complexes. One of the key unanswered questions was exactly where mitochondrial translation takes place, both in terms of the sub-compartments of individual mitochondria and within the entire mitochondrial network.

My project has involved developing a tool that allows us to visualise the localisation of mitochondrial translation within intact human cells. The click chemistry based method utilises modified amino acids that are incorporated into mitochondrial-encoded proteins and can be fluorescently labelled for visualisation by microscopy. I optimised and validated the robustness of the technique on a number of different human cell types including patient fibroblasts harbouring DNA mutations that cause mitochondrial disease.

Interestingly, the mitochondria surrounding the nucleus were found to be more translationally active than those out in the cellular periphery. By applying super resolution microscopy to look deep within mitochondria, I showed that mitochondrial translation takes place separate from the RNA granules in which RNA processing and ribosome assembly occurs. I also identified that unlike the situation in yeast, in human mitochondria translation primarily takes place in the cristae membranes – the same location that the fully functional OXPHOS complexes are found.

Currently I am applying the technique to flow cytometry so that complex samples, such as blood, can have the different cell types within them characterised in terms of mitochondrial translation. This will allow us to better understand the cell specificity and heterogeneity of mitochondrial function in health and disease.

Matt’s PhD project was funded by the ITN REMIX ((REgulation of MItochondrial gene eXpression) Network. To find out more, click here.

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