PROTEIN-PROTEIN INTERACTIONS INVOLVED IN PROTEASOMAL DEGRADATION
Overseen by Prof Jane Endicott, University of Oxford
Almost all proteins in mammalian cells are continuously degraded and re-synthetised. Protein degradation occurs mainly via the ubiquitin-mediated protein degradation pathway, also called the ubiquitin proteasome system (UPS). This pathway is initiated through the linkage of one or more ubiquitin moieties onto the target protein. Ubiquitylated substrates are then transported to the proteasome where degradation takes place. Proteasomes constitute up to 1% of the cellular protein mass and consist of a core unit (20S) and ring-shaped regulatory unit (19S), both composed of numerous polypeptide subunits. By controlling the concentration and thereby the activity of proteins essential to cellular life, the UPS regulates many critical eukaryotic cellular processes including the cell cycle, protein quality control and transcription. Dysfunction of the UPS has therefore been associated with the progression of various diseases, notably cancer and neurodegeneration.
This project aims to use biochemical, biophysical, structural and genetic approaches to define the molecular mechanisms by which ubiquitylated proteins are selectively targeted to the proteasome for degradation. To date, a number of receptors for ubiquitylated substrates have been identified within the proteasome, located in the 19S subunit. A subset of these ubiquitin receptors have also been detected in the cytoplasm, and have therefore been suggested to act as “shuttle factors” for delivery of ubiquitylated cargo. We are particularly interested in the shuttle protein Rpn10/Pus1, which has been found to interact with subunits of the 19S proteasome, such as Rpn1/Mts4 and Rpn12/Mts3. We aim to gain structural insights about these protein complexes through NMR spectroscopy as well as X-ray crystallography. Furthermore, in collaboration with Dr Colin Gordon’s research group at the University of Edinburgh, we plan to carry out in vivo studies in yeast to further characterise this network of interactions.
By elucidating the protein-protein interactions which maintain the 19S structure, as well as gaining more insights into the mechanisms for protein-delivery to the proteasome, we aim to provide the basis for therapeutic intervention in diseases where the UPS is deregulated.