Structural basis for multi-subunit assembly and substrate selection by the E3 ligase NRBP1

The ubiquitin-proteasome system regulates protein levels through their selective and programmed degradation and thus is implicated in almost all basic biological processes - such as DNA damage and repair, cell cycle, cell growth and proliferation and signal transduction. The pathway is often dysregulated in disease, either by failing to mark pathological proteins for degradation (faulty protein control system), or by erroneously leading necessary proteins to their destruction. The ubiquitylation machinery requires the cooperation of enzymatic proteins E1 and E2 that facilitate its universality allowing spanning of the proteome, and E3 ligases that confer its specificity by directly interacting with their protein substrates. I will determine the structure of the modular E3 ligases NRBP1 and UBR1, in complex with their respective proposed substrates BRI2 and RGS4 by X-ray crystallography. Complimentary techniques such as protein mass-spectrometry, biophysical and cellular assays, and screening of possible chemical modulators will help us uncover and perturb the structural basis of multi-subunit assembly and substrate selection of these E3 ligases. My studies will further our understanding of the molecular mechanisms underlying the regulation of ubiquitinylation machinery and the precise spatiotemporal control it exerts on each substrate, setting the foundations for the emerging field of re-directing and perturbing the proteolytic pathway at will. I aim to also shed light on the pathogenesis of Alzheimer's Disease, since both NRBP1 and UBR1's protein substrates have been implicated in amyloidogenic diseases.