Regulation of E2-25K sumoylation

Posttranslational modification with ubiquitin and SUMO (small ubiquitin related modifier) is essential to maintain cellular integrity. Sumoylation is a versatile modification and has been implicated in regulating protein interactions, cellular localisation, stability and activity of its target proteins. Sumoylation occurs via an ATP- dependent enzymatic cascade which includes E1, E2 and E3 enzymes. SUMO attachment can be reversed by a family of SUMO proteases. The proposed study is based on our recent finding that the ubiquitin conjugating enzyme E2-25K is a substrate for sumoylation. Biochemical data indicate that modification impairs formation of an ubiquitin thioester by E2-25K, a necessary step in the enzymatic cascade to attach ubiquitin to a target. This opens up the intriguing possibility that by inhibiting an ubiquitin E2, which potentially work with several E3s, can affect ubiquitination of a large set of substrates with widespread consequences for the cell. The aim of the proposed study is to identify and characterise the enzymes (SUMO E3 ligases and proteases) regulating E2-25K sumoylation in order to gain a deeper understanding of the functional significance of this modification in vivo. The expected results may contribute to a better understanding of the onset of neurodegenerative diseases like Alzheimers or Huntington disease.

Posttranslational modifications with ubiquitin and SUMO (small ubiquitin related modifier) are essential protein regulators involved in most cellular pathways. Deregulation of these modifications have severe consequences and are implicated in diseases like cancer or Alzheimer`s disease. Ubiquitin and SUMO are themselves small proteins which are reversibly attached to their substrates. This is depending on a tightly regulated enzymatic cascade, which involves the sequential action of a modifier specific E1 activating, E2 conjugating and E3 ligating enzyme for conjugation and specific enzymes for deconjugation. Regulation is mainly performed at the level of E3 ligating and deconjugating enzymes, since these components ensure substrate specificity. In our project supported by the FWF we were able to identify novel mechanisms of E2 deregulation.