Autophagy is an essential process in all eukaryotic cells and its malfunction is involved in numerous diseases, including neurodegenerative disorders. Extracellular vesicles play also an important role in such disorders. The γ-aminobutyric acid type A receptor-associated protein (GABARAP) and its close paralogs GABARAPL1 and -L2 constitute a subfamily of the autophagy-related protein 8 (Atg8) family. Being associated with a variety of dynamic membranous structures of autophagic and non-autophagic origin, Atg8 proteins functionalize membranes by either serving as docking sites for other proteins or by acting as membrane tethers or adhesion factors.

Subject of this project is the role of GABARAP subfamily members in the trafficking of membrane proteins such as receptors between different compartments, which is supported by a limited number of examples in the literature. Adding to these reports, our recent results indicate that deficiency for GABARAP but not of its close paralogs accelerates the degradation of EGFR upon ligand stimulation with concomitant impairment of signal transduction, alteration in target gene expression, EGF-uptake and EGFR vesicle composition over time. In the second funding period of this CRC framework we now aim to elucidate the structural foundations and mechanistic details of human EGFR sorting by Atg8 family proteins with a focus on GABARAP. This requires a combination of structural and functional approaches with studies in cells, accompanied by the need to expand the respective toolbox by generating further paralog specific antibodies or fluorescence-protein knock-in cell lines.

In order to obtain an unbiased view on the impact of GABARAP-subfamily members on receptor trafficking in general a surface proteome-based screening approach, followed by selection of promising candidates for in-depth investigation is also planned. Hits are to be analysed with respect to their trafficking (anterograde transport, internalisation, recycling, degradation) as well as signalling in the presence or absence of GABARAP subfamily proteins. Finally, proximity-based studies to analyse the role of GABARAP in secretion of membrane proteins via extracellular vesicles are envisaged. Overall, this project aims to provide a comprehensive view on a crucial aspect of membrane/vesicle dynamics affecting the establishment of cellular communication and identity.