Mitochondria are responsible for the energy supply of an organism and fulfill functions in metabolic and signaling processes. Researchers at the University Hospital Bonn (UKB) and the University of Freiburg have gained new insight into the organization of proteins in mitochondria. Their protein map represents an important basis for further functional characterization of the powerhouse of the cell.

The study is published in Nature in an article titled, “Mitochondrial complexome reveals quality control pathways of protein import.”

“Mitochondria have crucial roles in cellular energetics, metabolism, signaling, and quality control,” wrote the researchers. “They contain around 1,000 different proteins that often assemble into complexes and supercomplexes such as respiratory complexes and preprotein translocases. The composition of the mitochondrial proteome has been characterized; however, the organization of mitochondrial proteins into stable and dynamic assemblies is poorly understood for major parts of the proteome. Here we report quantitative mapping of mitochondrial protein assemblies using high-resolution complexome profiling of more than 90% of the yeast mitochondrial proteome, termed MitCOM.”

The team of researchers created a high-resolution image of the organization of proteins in protein complexes, known as MitCOM. MitCOM reveals the organization into protein complexes of more than 90% of the mitochondrial proteins from baker’s yeast.

Mitochondria import 99% of their proteins from the liquid portion of the cell, known as cytosol. In this process, a protein machinery called the TOM complex enables the uptake of these proteins through the membrane into the mitochondria. However, it is largely unclear how proteins are removed from the TOM complex when they get stuck during the transport process. The team led by Thomas Becker, PhD, professor, and Fabian den Brave, PhD, research group leader, both at the University of Bonn, used information from the MitCOM dataset. It was shown that non-imported proteins are specifically tagged for cellular degradation.

Further research by PhD student Arushi Gupta revealed a pathway by which these tagged proteins are subsequently targeted for degradation.

“The example from our study demonstrates the great potential of the MitCOM dataset to elucidate new mechanisms and pathways. Thus, this map of proteins represents an important source of information for further studies that will help us to understand the functions and origin of the cell’s powerhouse,” explained Becker, who is also director of the Institute of Biochemistry and Molecular Biology at UKB.