How are specific ubiquitin signals produced? How is the right target selected, modified at the right site, at the right time, in the right pathway? The range of signals that can be produced is dizzying, with multiple mono signals, poly signals, and branched signals all part of the cell’s repertoire. However, the mechanistic basis for specificity is still unclear.
We use a range of techniques, including X-ray crystallography, and two model systems to tackle these questions: 1) an exquisitely specific E3 ligase that targets one site for modification, functions with limited auxiliary enzymes including E2s, and performs only one type of ubiquitination. 2) a broad-spectrum, promiscuous ligase that uses multiple E2s, to effect multiple signals. Both models are pertinent to human disease, with the specific E3 ligase, FANCL, mutated in patients with Fanconi Anemia, and the broad spectrum ligase, Parkin, mutated in early onset Parkinsonism.
In recent years, we have defined the molecular basis both of specific E2 selection, and how non-selective broad-spectrum E2 use is achieved. We have determined the mechanism of regulation of Parkin via autoinhibition, and established the molecular basis for activation. Our detailed understanding of the specificity in the Fanconi Anemia pathway has allowed us to begin developing small molecules to target the pathway. Our future aims are to define the structural basis for target selection, and specific signal transfer.