Ubiquitin (Ub) and ubiquitin-like proteins (UBLs) play a role in a wide range of cellular processes including protein degradation, cell signaling, transcription regulation and DNA damage response. The regulation of numerous cellular processes by these proteins is ascribed to their ability to form a large spectrum of modifications. To date, besides ubiquitin that can modify a target protein with mono or poly-ubiquitin chains with varying linkages and length, more than dozen different UBLs are encoded in human genome, thereby significantly increase the repertoire of ubiquitin modifications. Not surprisingly, improper regulation of these modifications has been observed in many human diseases including cancer, Alzheimer's disease, Parkinson's disease and viral infections. My lab is interested in the molecular mechanisms governing Ub and UBL conjugation to cellular proteins. More than 900 enzymes are involved in deposition or removal of Ub/UBL from target proteins, and only little is known about their specificity, activity and interaction network. We use X-ray crystallography, enzymology, cell biology, biochemistry and a variety of biophysical methods in order to provide structural and functional data required for understanding the molecular mechanisms underlying the function of these enzymes.