Beyond Lysine Ubiquitination

The covalent attachment of ubiquitin to substrates controls virtually all aspects of the cell. With rare exceptions, ubiquitin was understood to exert its effects by becoming attached to the amino group of lysine residues within protein substrates. Recent discoveries from our lab and others have revealed that dedicated writers (E3 ligases) and erasers (DUBs) of non-lysine ubiquitination are intrinsic to eukaryotes. This highlights that attachment to sites beyond lysine are physiologically and perhaps pathologically important. These E3s tend to be highly divergent from their established counterparts and "activity-based" chemical biology approaches have been instrumental in identifying them. I will present work from my lab on technologies we have used to uncover unusual E3 ligases and the striking nature of their mechanism and substrate specificity. I will also discuss our characterisation of a small DUB family that is highly selective at removing ubiquitin from hydroxy amino acids. These new developments indicate that non-lysine ubiquitination is an integral component of the ubiquitin system that is subject to sophisticated regulation.