This week, it is Mitochondrial Disease Awareness Week. Therefore we would like to take the opportunity to talk about the mitochondrial proteome, the work we do within this field, and you will even get to meet one of our researchers, involved in this work.

The mitochondria are distributed throughout the cytoplasm of the cell, each organelle enclosed by a double membrane, the inner one forming the characteristic folds known as cristae. Mitochondria are essential for producing the cell´s need of ATP through cellular respiration, but have also been shown to participate in many other cellular functions, including apoptosis, calcium storage and cellular signaling. The human mitochondrial proteome has been estimated to contain between 1000-1500 proteins, although less than 500 proteins have experimental evidence for mitochondria in the UniProt database. Spatial proteomics is a key method to further explore the mitochondrial proteome, with the ultimate goal of enabling a deeper understanding of the many functions of the mitochondria.

Mikaela Wiking is a PhD student and research engineer in the Cell Profiling group within the Human Protein Atlas. The group responsible for identifying the subcellular localization of all human proteins, and the mitochondrial proteome is part of this effort.

– I joined the group in 2009 as a technician, and later I became a laboratory engineer, and eventually research engineer. In parallel, I started my PhD studies in 2013.

So, Mikaela divides her time in the group between working in the production, and doing her own research. Even though it might seem like a fragmented way to work, Mikaela actually likes the setup.

– We are several persons in our group with this kind of arrangement, and it is working out just fine for us. The days are full of action, there is always something going on.

In her PhD project Mikaela is investigating the proteins localizing to the mitochondria, and she and her co-workers have identified more than 700 proteins so far, including proteins lacking experimental localization data in UniProt.

– By combining antibody-based protein profiling with high-resolution confocal microscopy, we have shown that a subset of these proteins localize only to the mitochondria whereas nearly half of the proteins can be detected in additional cellular locations as well, mainly the cytoplasm, nucleus or nucleoli.

Immunofluorescence is particularly suited for studying multiple localizations of proteins, as it relies on the specificity of antibodies, which can be confirmed with e.g. knockdown with siRNA. Visualization of proteins located in multiple organelles is easily enabled in fixed cell samples, as it does not require purification of mitochondrial fractions. The multi-localization of mitochondrial proteins has been suggested for both human cells, as well as other species, before but not to such a high extent. Hopefully, the work of Mikaela and other members of the Cell Profiling group in charachterizing the mitochondrial proteome will enable a deeper understanding of the many functions of the mitochondria.

Read more about the mitochondria in this review.