Public release date: 10-Feb-2012
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Contact: Dr. Ralf Erdmann
Ralf.Erdmann@rub.de
49-234-322-4943
Ruhr-University Bochum

The group of Prof. Dr. Ralf Erdmann at the Ruhr-Universit?t Bochum (Faculty of Medicine, Department of Systems Biochemistry) discovered a connection of peroxisomal protein import and receptor export. In the Journal of Biological Chemistry, they disclosed that enzymes only get imported into certain cell organelles (peroxisomes) upon coupling of their import to the recycling of their transport protein (receptor).

Multi-functional tool peroxisome

Peroxisomes do not have their own DNA. Thus, all peroxisomal proteins are coded within the nucleus and imported into the peroxisome after their synthesis is completed. The Erdmann lab investigates this process in detail. Peroxisomes contain more than 50 various enzymes in total which e.g. decompose fatty acids and dispose hydrogen peroxide or plasmalogens, the main phospholipid of the white matter of the brain. A disruption of their function does not only cause severe metabolic disorders, it can even lead to death of newborns.

Export signal controls recycling

Dynamic receptors recognize and escort the enzymes destined for the peroxisome to the organelle where they attach to the membrane. Then the receptor-enzyme complex disassembles and the enzyme is transported across the peroxisomal membrane. Afterwards, the receptor is transported from the membrane back to the cytosol. This recycling is controlled by the attachment of the small protein ubiquitin to the receptor, which functions as an export signal.

Modification as a safety barrier

The team of Prof. Dr. Ralf Erdmann studied a certain peroxisomal receptor, which consists of a targeting unit (Pex18p) and an enzyme-binding unit (Pex7p). The scientists discovered that ubiquitin modifies Pex18p in order to enable the receptor to return to the intracellular liquid. Only when the targeting unit of the receptor is exported from the membrane, the import of the cargo-loaded enzyme-binding unit takes place. This result supports the export-driven-import model, previously proposed by the Erdmann group.

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Bibliographic record

A. Hensel, S. Beck, F. El Magraoui, H.W. Platta, W. Girzalsky, R. Erdmann (2011): Cysteine-dependent ubiquitination of Pex18p is linked to cargo translocation across the peroxisomal membrane, Journal of Biological Chemistry, doi: 10.1074/jbc.M111.286104

W. Schliebs, W. Girzalsky, R. Erdmann (2010): Peroxisomal protein import and ERAD: variations on a common theme, Nature Reviews Molecular Cell Biology, doi: 10.1038/nrm3008

Further information

Prof. Dr. Ralf Erdmann, Department of Biochemistry Systems, Faculty of Medicine of the Ruhr-Universit?t Bochum, 44780 Bochum, Germany, Phone: +49/234/32-24943 Ralf.Erdmann@rub.de

Click for more

Department of Biochemistry Systems
http://www.ruhr-uni-bochum.de/physiolchem/system/index.html.en

Previous press information on the topic
http://aktuell.ruhr-uni-bochum.de/pm2011/pm00233.html.en

Figure online

A figure related to this press release can be found at http://aktuell.ruhr-uni-bochum.de/pm2012/pm00024.html.en

Editor

Marie-Astrid Reinartz

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Read the rest here:
No entry without protein recycling: RUB researchers discover new coherence in enzyme transport