Dr. Johannes Freitag

Research:

Eukaryotic cells contain specialized reaction chambers termed organelles such as mitochondria and peroxisomes. While many proteins exclusively localize in a single organelle, others reside in two or more compartments or translocate from one to the other. We study regulation of dual localization, the underlying molecular mechanisms and how this affects organelle communication, organelle contact sites and cellular physiology. In our projects we combine genetic screening and interaction analysis, in vitro reconstitution assays and microscopy in unicellular model systems including Saccharomyces cerevisiae and Ustilago maydis. Understanding proteins with diverse destinations and their trafficking routes is critical to decipher how organelles interact, but still preserve their identity. Moreover, we utilize peroxisomes as a model to address another fundamental question in cell biology – the development of organelle subpopulations with a specialized proteome. Can we define a code for segregation of unique peroxisome populations? 

Funding and Awards: 

2021 – 2024 DFG Research Grant “Protein transit from mitochondria to peroxisomes”

2015 – 2017 Fellowship from the German National Academy of Sciences Leopoldina

2013 – 2015 Fellowship from LOEWE and Senckenberg society

2013             PhD Award of the University of Marburg

Publications: 

* equal contribution § corresponding author

18. Klemm P, Christ M, Altegoer F, Freitag J, Bange G, Lechner M (2022). Evolutionary reconstruction, nomenclature and functional meta-analysis of the Kiwellin protein family. Front Plant Sci. 13:1034708.

17. Ast J, Bäcker N, Martorana D, Renicke C, Stehlik T, Heimerl T, Taxis C, Bange G, Bölker M, Sandrock B, Schink KO and Freitag J§ (2022) Selective accumulation of matrix proteins inside of peroxisomal subdomains. bioRxiv 2022.10.02.510529.

16. Stehlik T, Bittner E, Lam J, Dimitrov L, Schöck I, Harberding J, Heymons N, Schuldiner M, Zalckvar E, Bölker M, Schekman R and Freitag J§ (2022) Dually targeted proteins regulate proximity between peroxisomes and partner organelles. bioRxiv: 2022.07.29.501968.

15. Bittner E, Stehlik T, and Freitag J§  (2022) Sharing the wealth - the versatility of proteins targeted to peroxisomes and other organelles. Front Cell Dev Biol. 10.3389/fcell.2022.934331.

14. Becker F, Linne U, Xie X, Hemer A-L, Bölker M, Freitag J§ and Sandrock B (2022) Import and Export of Mannosylerythritol Lipids by Ustilago maydis. mBio e02123-22.

13. Ast J, Bäcker N, Bittner E, Martorana D, Ahmad H, Bölker M and Freitag J§ (2022) Two Pex5 Proteins With Different Cargo Specificity Are Critical for Peroxisome Function in Ustilago maydis. Front Cell Dev Biol. 10.3389/fcell.2022.858084.

12. Becker, F,  Stehlik, T, Linne, U, Bölker, M, Freitag, J, and Sandrock, B. (2021). Engineering Ustilago maydis for production of tailor-made mannosylerythritol lipids. Metab. Eng. Commun. 12, e00165.

11. Wege, S-M, Gejer, K, Becker, F, Bölker, M, Freitag, J, and Sandrock, B (2021). Versatile CRISPR/Cas9 Systems for Genome Editing in Ustilago maydis. J. Fungi 7, 149. 

10. Stehlik, T, Kremp, M, Kahnt, J, Bölker, M  & Freitag, J§ (2020). Peroxisomal targeting of a protein phosphatase type 2C via mitochondrial transit. Nature Communications 11, 2355.

9.  Kremp, M, Bittner, E, Martorana, D, Klingenberger, A, Stehlik, T, Bölker, M & Freitag J§ (2020) Non-AUG Translation Initiation Generates Peroxisomal Isoforms of 6-Phosphogluconate Dehydrogenase in Fungi. Front. Cell Dev. Biol. 8, 251. 

8.  Freitag J, Stehlik T, Stiebler AC & Bölker M (2018) The Obvious and the Hidden: Prediction and Function of Fungal Peroxisomal Matrix Proteins. Proteomics of Peroxisomes 139-155.

7.  Stehlik, T, Sandrock, B, Ast, J, & Freitag, J§ (2014) Fungal peroxisomes as biosynthetic organelles. Curr. Opin. Microbiol. 22, 8–14. 

6. Stiebler AC*, Freitag J*, Schink KO, Stehlik T, Tillmann BAM, Ast J & Bölker M (2014) Ribosomal   Readthrough at a Short UGA Stop Codon Context Triggers Dual Localization of Metabolic Enzymes in Fungi and Animals. PLOS Genetics 10: 1–9.

5. Freitag J, Ast J, Linne U, Stehlik T, Bölker M & Sandrock B (2014) Peroxisomes contribute to biosynthesis of extracellular glycolipids in fungi. Molecular Microbiology 93: 24–36. 

4. Heimel K*, Freitag J*, Hampel M, Ast J, Bölker M & Kämper J (2013) Crosstalk between the unfolded protein response and pathways that regulate pathogenic development in Ustilago maydis. Plant Cell 25: 4262–4277.

3. Ast, J, Stiebler, A. C, Freitag, J, & Bölker, M (2013). Dual targeting of peroxisomal proteins. Front. Physiol. 4: 296. 

2.  Freitag J, Ast J & Bölker M (2012) Cryptic peroxisomal targeting via alternative splicing and stop codon read-through in fungi. Nature 485: 522–525. 

1.  Freitag J*, Lanver D*, Böhmer C, Schink KO, Bölker M & Sandrock B (2011) Septation of infectious hyphae is critical for appressoria formation and virulence in the smut fungus Ustilago maydis. PLoS Pathogens. 7: e1002044.