"Ubiquitination is a reversible post-translational modification (PTM) regulating diverse cellular functions including cell cycle, apoptosis, gene expression, inflammation and DNA repair. Ubiquitination results in the tagging of proteins with either monoubiquitin or polyubiquitin chains of different linkages that are structurally distinct. Given that protein ubiquitination is involved in so many cellular processes, it needs to be under very tight regulation. Protein ubiquitination is reversed by deubiquitinases (DUBs), which are specialized proteases that cleave the isopeptide linkage between ubiquitin molecules in chains or between ubiquitin and protein substrates. The objective of this study is to understand how substrate specificity is determined and in particular, how function of the A20-family of ovarian tumour (OTU) DUBs is regulated. I will crystallize the catalytic domains of OTU family DUBs involved in cell signalling, to understand their ubiquitin chain linkage specificity. I intend to establish how the interacting scaffolding proteins of A20-like DUBs, such as ABIN and TAX1BP1, mediate substrate targeting and specificity, and allosterically regulate enzyme activity. I shall express full-length protein complexes of A20 and Cezanne together with their interacting proteins using multi-gene baculovirus and mammalian systems. I will use X-ray crystallography and electron microscopy to understand the structure and conformational changes regulating DUB complex activation. The structural insights obtained will be used to understand oncogenic DUB mutants, and establish how DUB dysregulation leads to tumorigenesis. Lastly, I will analyze how reversible oxidation regulates DUBs during signalling. The proposed structural and biochemical characterisation of the multi-subunit protein complexes of DUBs will help define the molecular details of allosteric mechanisms governing A20-like DUBs and provide the basis for design of pharmaceutical modulators of DUB activity."