Evolution of cellular power stations

Mitochondria originate from a bacterium, meaning they have their own DNA molecule in which the structure of several proteins is recorded. An OXA-like machinery already existed in the bacterial precursor of mitochondria and has been conserved throughout evolution. The proteins produced according to the mitochondrion's genetic material are integrated by the OXA into the inner mitochondrial membrane. The genetic information of 99 percent of the proteins comprising mitochondria are stored in the cell's nucleus, however. The cell produces these protein molecules in the cytoplasm, after which the TOM, or "Translocase of the Outer Membrane," and the TIM, "Translocase of the Inner Membrane," transport them across the outer and inner membranes into mitochondria. How many of these imported proteins are also integrated into the inner membrane by OXA was unclear until now.

The researchers from the University of Freiburg systematically searched for proteins integrated by OXA into the inner membrane after they had been imported via TOM and TIM. They used an analytical technique called quantitative mass spectrometry to identify mitochondrial inner membrane proteins which are reduced in cells without OXA. By tracing the integration of radioactively labelled proteins into the inner mitochondrial membrane, they were able to prove that OXA is necessary for this process.

The imported OXA-dependent proteins play important functions that range from cellular respiration, the exchange of metal ions, and biochemical reactions, to the integration of proteins enabling the transfer of metabolic products across the inner membrane. When the integration or function of these respiratory proteins is blocked, this can cause mitochondrial-based neuromuscular diseases or cancer. The OXA-dependent integration of inner membrane proteins, which has been conserved throughout evolution, is thus fundamental for the formation of the mitochondrial inner membrane and for the energy supply of human cells.

Nikolaus Pfanner and Nils Wiedemann are leaders of research groups at the Institute for Biochemistry and Molecular Biology of the University of Freiburg. Sebastian Stiller is a researcher in Wiedemann's lab, while Jan Höpker is a former member of Pfanner's research group. Bettina Warscheid is a professor at the Institute of Biology II of the University of Freiburg, and Silke Oeljeklaus is a researcher in Warscheid's lab. Pfanner, Warscheid and Wiedemann are all members of the Cluster of Excellence BIOSS Centre for Biological Signalling Studies as well as the Spemann Graduate School of Biology and Medicine of the University of Freiburg.