In signal transduction – as in business – location is key. This is epitomized by neurotransmitter transporters, which must be delivered to the presynaptic specialization to accomplish their namesake action, i.e., the retrieval of released neurotransmitters from the synaptic cleft. Thus, our current work focuses on understanding how signaling molecules (G protein-coupled receptors, transporters) reach their site of action, i.e., specialized compartments of the cell surface. The working hypothesis assumes that sorting decisions are already made at the site where the membrane proteins are born, that is the endoplasmic reticulum (ER). Accordingly, we study how the proteins mature and reach the ER exit sites to recruit the COPII (coatomer proteins II) coat. At the other end, i.e., at the cell surface, we explore, how proteins are trapped in microcopartments by examining their diffusion rate and their lateral mobility.
Biochemistry/molecular pharmacology (protein purification, mass spectrometry; enzyme/transport assays, binding assays, immunoblotting ...); cellular and molecular biology (primary cells/established cell lines; transfections, site-directed mutagenesis; immunocytochemistry, confocal microscopy; fluorescence resonance energy transfer; single molecule tracking ...)
1. Milan-Lobo L, Gsandtner I, Gaubitzer E, Rünzler D, Buchmayer F, Köhler G, Bonci A, Freissmuth M, Sitte HH (2009) Subtype-specific differences in corticotropin-releasing factor receptor complexes detected by fluorescence spectroscopy. Mol Pharmacol. 76:1196-210.
2. Sarker S, Weissensteiner R, Steiner I, Sitte HH, Ecker GF, Freissmuth M, Sucic S (2010) The high-affinity binding site for tricyclic antidepressants resides in the outer vestibule of the serotonin transporter. Mol Pharmacol 78:1026-1035
3. El-Kasaby A, Just H, Malle E, Stolt-Bergner PC, Sitte HH, Freissmuth M, Kudlacek O (2011) Mutations in the carboxyl-terminal SEC24 binding motif of the serotonin transporter impair folding of the transporter. J Biol Chem 285:39201-39210
4. Sucic S, El-Kasaby A, Kudlacek O, Sarker S, Sitte HH, Marin P, Freissmuth M (2011) The Serotonin Transporter Is an Exclusive Client of the Coat Protein Complex II (COPII) Component SEC24C. J Biol Chem 286:16482-16490
5. Geetha N, Mihaly J, Stockenhuber A, Blasi F, Uhrin P, Binder BR, Freissmuth M, Breuss JM (2011) Signal integration and coincidence detection in the mitogen-activated protein kinase/ERK-cascade: Concomitant activation of receptor tyrosine kinases and of LRP-1 leads to sustained ERK phosphorylation via downregulation of dual specificity phosphatases (DUSP-1 and -6). J Biol Chem 286:25663-25674.