Monoamine transporters and adenosine receptors in neurons
G protein-dependent signaling; G protein-coupled receptors; SLC6 neurotransmitter transporters; ER export of membrane proteins
Research interest of the Faculty Member
Dr. Freissmuth is interested in the mechanisms underlying the regulation of neurotransmitter transporters, in particular the serotonin transporter, the current focus is on their folding in the endoplasmic reticulum (ER), their oligomeric assembly, and their trafficking through the secretory pathway and axonal delivery. In addition, the transport cycle is being explored (including substrate and inhibitor binding) to understand the mechanistic basis for the action of amphetamines. The second area of interest is focused on GPCRs, in particular adenosine receptors. In the recent past, Dr. Freissmuth investigated the role of accessory proteins that impinged on the fate of the receptors during folding and maturation and factors that restricted the mobility of the receptors at the cell surface.
Collaborating research groups where PhD Students could perform their research stay abroad
- Joel Bockaert, Institut de Génomique Fonctionnelle, Montpellier
- Randy Schekman, Dept. of Mol. and Cell Biology, Universityt of Califronia. Berkeley
- Jennifer Whistler, Ernest Gallo Clinic and Research Center, Univ. California, San Francisco
Know-how and infrastructure of the research group
This research group was the first to describe Gs-independent signaling of the A2A-receptor (Sexl et al., 1997) and to link this to recruitment of ARNO (Gsandtner et al., 2005). The deubiquinating enzyme USP4 was also identified as an interactor that determined the fate of the A2A-receptor at the level of the ER (Milojevic et al., 2006). Following up on the observation that neurotransmitter transporters of the SLC6 family are constitutive oligomers, the group developed two concepts, namely that oligomerization was required for the actions of amphetamine (N-terminal lever hypothesis, see Seidel et al., 2005, Sucic et al., 2010) and that oligomerization was required for ER export. This work identified of the ER export motif on the GABA-trasnporter-1/GAT1 (Farhan et al., 2004, 2007 & 2008) and showed that recruitment of SEC24D was required for axonal targeting of GAT1 (Reiterer et al., 2008). More recently, the serotonin-transporter (SERT) was shown to differ from its related transporters (NET, DAT, GAT1) by requiring SEC24C (Sucic et al., 2011).
The group uses various techniques of fluorescence microscopy including resonance energy transfer, correlation spectroscopy and single dye tracking. These experiemnts are done in both, cell lines and primary neurons (including primary serotoninergic neurons prpeared from raphe nuclei). The lab also has an established track record in protein purification and reconstitution experiments. The laboratories are equipped with the pertinent hardware (FPLC, mass spectrometers, cell culture facilities, epifluorescence and confocal microscopes).