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Sven Fischer

Sven Fischer

Regulation of the peroxisomal import receptor Pex5p

Principal investigator: Prof. Dr. Bettina Warscheid

Institut für Biologie II
Schänzlestr. 1
79104 Freiburg

Phone: +49 (0) 761 203 xxx


Peroxisomes are metabolic organelles that are present in almost all eukaryotic cells. They are multi-purpose organelles dynamically adapting their size, number and protein composition in response to environmental changes and metabolic needs. In addition to their common and conserved functions in fatty acid beta-oxidation and the detoxification of hydrogen peroxide produced by oxidases residing in the peroxisome, they are involved in a variety of organism- and cell type-specific functions like the biogenesis of antibiotics in certain filamentous fungi or chemiluminescent reactions in fireflies. In humans, the synthesis of bile acid and ether phospholipids are localized in peroxisomes and dysfunctional peroxisomes can lead to severe diseases like the X-linked adrenoleukodystrophy or the Zellweger Syndrome, which leads to death in early infancy.

Peroxisomal proteins are nucleus-encoded and posttranslationally imported into the organelle in a folded and even oligomeric state through distinct transient import pores. In my work, I study the role of Pex5p phosphorylation for the regulation of the peroxisomal matrix protein import in the eukaryotic model organism Saccharomyces cerevisiae. Pex5p is a cytosolic receptor that binds cargo proteins containing a specific, C-terminal peroxisomal targeting sequence (PTS1) and, together with membrane-bound Pex14p, promotes pore formation and cargo translocation. We use high-resolution mass spectrometry to map and quantify Pex5p in vivo and in vitro phosphorylation-sites and to identify the kinases mediating the phosphorylation events in combination with molecular genetics, biochemical assays and fluorescence microscopy for functional analyses.


  • Yeast cultivation
  • Mass spectrometry
  • Recombinant protein expression and purification
  • Affinity purification
  • Molecular biology and yeast genetics
  • Fluorescence microscopy
  • Basic biochemistry
  • Chemical cross-linking


[1] S. Hagen, F. Drepper, S. Fischer, K. Fodor, D. Passon, H. W. Platta, M. Zenn, W. Schliebs, W. Girzalsky, M. Wilmanns, B. Warscheid, and R. Erdmann, “Structural insights into cargo recognition by the yeast PTS1 receptor,” J. Biol. Chem., vol. 290, no. 44, pp. 26610–26626, 2015.

[2] A. Chan, A. Schummer, S. Fischer, T. Schröter, L. D. Cruz-Zaragoza, J. Bender, F. Drepper, S. Oeljeklaus, W.-H. Kunau, W. Girzalsky, B. Warscheid, and R. Erdmann, “Pex17p-dependent assembly of Pex14p/Dyn2p-subcomplexes of the peroxisomal protein import machinery,” Eur. J. Cell Biol., vol. 95, no. 12, pp. 585–597, 2016.

[3] Schummer A, Fischer S, Oeljeklaus S, Warscheid B., "Study of Peroxisomal Protein Phosphorylation by Functional Proteomics," Methods Mol Biol. 2017;1595:267-289. doi: 10.1007/978-1-4939-6937-1_26.