Interplay of cargo receptors in aggrephagy

Autophagy (Greek for self-eating) is a process in which cells encapsulate and finally degrade damaged and harmful material that accumulates in them. The encapsulation occurs by the formation of a membrane structure around the substances destined for degradation. When the membrane has fully enwrapped the harmful cargo material is closes to form an autophagosome. The autophagosome subsequently fuses with the cells recycling stations, the lysosomes, wherein the material is broken down and the individual building blocks are recycled and reused. The whole process is analogous to a waste bag (the membrane) wrapping around the waste, just that in our cells the bag is made anew locally at the cargo material. The process of autophagy is important for our health and defects in autophagy have been linked to severe disease such as neurodegeneration and cancer. In this project, we will focus on the degradation of protein aggregates by the autophagy machinery. This is an important question because the accumulation of protein aggregates occurs in diseases such as Alzheimer disease and Parkinson disease. In order to shed light on this process, we will employ biochemical reconstitution experiments including physiologically relevant substrates as well as cell biological experiments to understand how cargo selection and autophagosome biogenesis are coupled. In addition, we will dissect at which point the machinery is stalled in the handling of pathological substrates. Special attention will be given to the interaction of the NBR1 and TAX1BP1 cargo receptors, which recognize the aggregated proteins, the recruitment and activation of the autophagy machinery to the cargo by the cargo receptors as well as the interaction of the selective autophagy machinery with monomeric and brain-derived fibrillar cargo proteins. We will employ biochemical reconstitution experiments using purified proteins and vesicles isolated from cells as well as brain-derived protein fibrils. We will also pursue cell biological approaches to test the relevance of our in vitro experiments in cells and structural biology approaches to obtain detailed mechanistic insights into the interaction of the factors under investigation. We expect to gain unique mechanistic insights into the interplay of cargo receptors in the degradation of ubiquitinated and/or misfolded protein by aggrephagy. We will also, for the first time, study the interaction of this machinery with physiological cargoes and brain-derived protein aggregates. Furthermore, the inclusion of other factors of the proteostasis network such as chaperones and the ubiquitination machinery, will provide important insights into the integration of selective autophagy into this network.