Foto: Universität Stuttgart / Max Kovalenko

Mitochondrial Protein Translocation

Professor Nussberger

Channeling proteins across biological membranes through nanometer-scale pores is an essential process that occurs in all living organisms. Prominent examples are the protein secretory pathways of bacteria as well as the movement of proteins across membranes of eukaryotic organelles such as the endoplasmic reticulum, peroxisomes, chloroplast and mitochondria.

The main focus of this  research topic is to understand the mechanism of transfer of mitochondrial preproteins through the preprotein-conducting channel of the outer membrane of mitochondria (TOM) at a molecular level.

Our experiments are mainly performed with isolated and purified membrane protein components. Single-particle electron cryo-microscopy  - carried out in collaboration with the laboratory of Prof. Werner Kühlbrandt (MPI of Biophysics, Frankfurt) - provided detailed insights into the molecular architecture of the mitochondrial preprotein import machinery TOM at 3.3 Å resolution. The structure of TOM revealed a 148 kDa symmetrical dimer of ten membrane protein subunits that create a shallow funnel on the cytoplasmic membrane surface. In the core of the dimer, the β-barrels of the Tom40 pore form two identical preprotein conduits. Each Tom40 pore is surrounded by the transmembrane segments of the α-helical subunits Tom5, Tom6, and Tom7. Tom22, the central preprotein receptor, connects the two Tom40 pores at the dimer interface. We are now focussing  on the mechanism of protein translocation using various electrical and optical single-molecule techniques.

Selected Publikations:

  • New insights into the structure and dynamics of the TOM complex in mitochondria. Nussberger, S., Ghosh, R. & Wang, S. Biochemical Society Transactions 52:911-922, DOI 10.1042/BST20231236 (2024) (Journal cover)
  • Tracking the activity and position of mitochondrial β-barrel proteins. Wang, S. & Nussberger, S. Methods Mol. Biol. 2778: 221-236, DOI 10.1007/978-1-0716-3734-0_14 (2024) (Journal cover)
  • Ornelas, P., Bausewein, T., Martin, J., Morgner, N., Nussberger, S. & Kühlbrandt, W. Two conformations of the Tom20 preprotein receptor in the TOM holo complex. Proceedings of the National Academy of Sciences, USA:120 (34), e23014471, DOI 10.1073/pnas.2301447120 (2023) (Journal cover)
  • Wang, S. & Nussberger, S. Single-molecule imaging of lateral mobility and ion channel activity in lipid bilayers using total internal reflection fluorescence (TIRF) microscopy. J. Vis. Exp. (JoVE) 192: 1-21, e64970, DOI 10.3791/64970 (2023)
  • Wang, S., Findeisen, L., Leptihn, S., Wallace, M.I., Hörning, M. & Nussberger, S. Spatiotemporal stop-and-go dynamics of the mitochondrial TOM core complex correlates with three-state channel activity. Communications Biology: DOI 10.1038/s42003-022-03419-4 (2022)
  • Bausewein, T., Naveed, H., Liang, J. & Nussberger, S. The structure of the TOM core complex in the mitochondrial outer membrane. Biological Chemistry: DOI 10.1515/hsz-2020-0104 (2020)
  • Bausewein,T., Mills,D.J., Langer, J.D., Nitschke, B., Nussberger, S. & Kühlbrandt, W. Cryo-EM structure of the TOM core complex from Neurospora crassa. Cell,170: 693–700 (2017)
  • Mahendran, K.R., Romero-Ruiz, M., Schlösinger, A., Winterhalter, M., & Nussberger, S. Protein translocation through TOM40: Kinetics of peptide release. Biophys. J., 102:39-47 (2012)
  • Gessmann, D., Flinner, N., Pfannstiel, J., Schlösinger, A., Schleiff, E., Nussberger, S., & Mirus, O. Structural elements of the mitochondrial preprotein-conducting channel Tom40 dissolved by bioinformatics and mass spectrometry. Biochim. Biophys. Acta - Bioenergetics, 1807:1647-1657 (2011)
  • Mager, F., Gessmann, D., Nussberger, S. & Zeth, K. Functional refolding and characterization of two Tom40 isoforms from human mitochondria. J. Membr. Biol., 242: 11-21 (2011)
  • Mager, F., Sokolova, L., Lintzel, J., Brutschy, B., & Nussberger, S. LILBID-mass spectrometry of the mitochondrial preprotein translocase TOM. J. Physics Condensed Matter, 22: 454132 (7pp) (2010)
  • Romero-Ruiz, M., Mahendran, K.R., Eckert, R., Winterhalter, M., & Nussberger, S. Interactions of mitochondrial presequence peptides with the mitochondrial outer membrane preprotein translocase TOM. Biophys. J., 99: 774-81 (2010)
  • Poynor, M., Eckert, R. & Nussberger, S. Dynamics of the preprotein translocation channel of the outer membrane of mitochondria. Biophys. J., 95:1511-22 (2008)
  • Nussberger, S. & Neupert, W.: The preprotein translocation channel of the outer membrane ofmitochondria. In: Structure and Dynamics of Confined Polymers, Kasianowicz J.J. et al. eds., NATO Science Series, Kluwer Academic Publishers. Dordrecht, Boston, London, Vol. 87, 67-84 (2002)
  • Ahting, U., Thieffry, M., Engelhardt, H., Hegerl, R., Neupert, W. & Nussberger, S.: Tom40, the main component of the protein conducting TOM channel in the outer membrane of mitochondria. J. Cell Biol. 153, 1151-1160 (2001).
  • Ahting, U., Thun, C., Hegerl, R., Typke, D., Nargang, F.E., Neupert, W., & Nussberger, S. : The TOM core complex: The general protein import pore of the outer membrane of mitochondria. J. Cell Biol. 147, 959-968 (1999) (Journal cover)
  • Künkele, K.P., Heins, S., Dembowski, M., Nargang, F.E., Benz, R., Thieffry, M., Lill, R., Nussberger, S., & Neupert, W.: The preprotein translocation channel of the outer membrane of mitochondria. Cell 93, 1009-1019 (1998)

Contact

 

Biophysics Group, Institute of Biomaterials and biomolecular Systems, University of Stuttgart

Pfaffenwaldring 57 , D-70569 Stuttgart, Germany

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