Ruprecht-Karls-Universität Heidelberg

Matthias Seedorf
Project Group Leader in the
ZMBH

ZMBH
Im Neuenheimer Feld 282
69120 Heidelberg, Germany
Tel.: + 49-6221 54 8299.
Fax: +49-6221 54 5892.
m.seedorf@zmbh.uni-heidelberg.de


Coupling of ER and plasma membrane


Most secreted and membrane proteins contain hydrophobic signal sequences that target their synthesis to the endoplasmic reticulum (ER). Beside that, certain mRNAs are transported within the cell, suggesting a local protein synthesis at specific domains of the ER. We have worked in yeast on the biogenesis of the polytopic membrane protein Ist2, which mRNA is localized to the periphery of daughter cells. In addition to local protein synthesis, Ist2 utilizes a lipid-binding signal for rapid accumulation at the cortical ER. Attached to other membrane proteins this signal targets the resulting chimeras to domains of the cortical ER, bypassing transport along the secretory (Sec)-pathway and protein degradation. Ist2 shows similarity to the TMEM16 protein family, of which two mammalian members have been identified as calcium activated chloride channels of the plasma membrane. Whether Ist2 functions in a similar manner at domains of the cortical ER or whether Ist2 reaches the plasma membrane by a sec-independent pathway remains one of our major future questions.

We use the model system Saccharomyces cerevisiae, in order to

  • Identify additional lipids and/or proteins that are responsible for the accumulation of Ist2 at the cortical ER. This includes the combination of yeast genetics with biochemical approaches including in vitro lipid-binding experiments. In the future, we will study the features of the Ist2 sorting signal and its interaction with membranes in detail;

  • Analyze the function of Ist2 as a channel protein and localize the protein precisely.

  • In addition, we employ mammalian tissue culture cells and study the trafficking of Ist2 and compare it to STIM proteins, which contain similar sorting signals as Ist2. STIM proteins function as calcium sensors of the ER and recruit ER domains to the plasma membrane. Thereby these proteins couple the uptake of extracellular calcium with calcium uptake into the ER. 


 

Selected publications

Ercan, E., Momburg, F., Engel, E., Temmerman, K., Nickel, W. and M. Seedorf (2009). A conserved, lipid-mediated sorting mechanism of yeast Ist2 and mammalian STIM proteins to the peripheral ER. Traffic 10:1802-1818.

Fischer, M.A., Temmerman, K., Ercan, E., Nickel, W. and M. Seedorf (2009). Binding of the plasma membrane lipids recruits the yeast integral membrane protein Ist2 to the cortical ER. Traffic, 10, 1084-1097.

Maass, K., Fischer, M.A., Seiler, M., Temmerman, K., Nickel, W. and M. Seedorf (2009). A signal comprising a basic cluster and an amphipathic α-helix interacts with lipids and is required for the transport of Ist2 to the yeast cortical ER. Journal of Cell Science, 122, 625- 635.

Nickel, W. and M. Seedorf (2008). Unconventional Mechanisms of Protein Transport to the Cell Surface of Eukaryotic Cells. Annual Review of Cell and Developmental Biology, 24, 287-3082.

Jüschke, C., Wächter, A., Schwappach, B. and Seedorf, M. (2005). SEC18/NSF-independent, protein-sorting pathway from the yeast cortical ER to the plasma membrane. J. Cell Biol. 169:613-622.

Jüschke, C., Ferring, D., Jansen, R.-P. and Seedorf, M. (2004). A novel transport pathway for a yeast plasma membrane protein encoded by a localized mRNA. Current Biology 14:406-411.

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