Ubiquitylation (or ubiquitination), is a post-translational modification that is essential for the functioning of eukaryotic cells. E2 conjugating enzymes (E2s) and E3 ligases drive the ubiquitylation cascade that ultimately leads to the specific recognition and attachment of ubiquitin to a myriad of substrates.

Ubiquitylation is reversed by a specific class of enzymes termed deubiquitylating enzymes (DUBs). Since its discovery, ubiquitylation has been regarded as a post-translational modification that specifically targets lysine side chains and protein N-termini (canonical ubiquitylation). However, recent discoveries demonstrated that also serine and/or threonine residues as well as other biological molecules can be targeted by ubiquitylation (non-canonical ubiquitylation) [1,2].  We also recently found that the Machado-Josephin disease DUB family, in particular its poorly characterized member JOSD1, specifically cleaves the ester bond linking ubiquitin to threonine substrates but is unable to cleave the isopeptide bond linking ubiquitin to lysine [3].

The identification of ubiquitin enzymes that are able to specifically attach or remove ubiquitin from non-canonical residues clearly demonstrates that non-lysine ubiquitylation is relevant in eukaryotes cells. To date, there have been limited research efforts focused on either the identification of additional non-canonical ubiquitin enzymes or on the development of enabling technologies to identify non-canonical ubiquitylation events at a proteomic level. To determine the extent and to understand the biological impact of this previously unappreciated ubiquitin modification forms the main goal of my research group.

My research aims to identify and characterize (1) ubiquitin enzymes responsible for non-canonical ubiquitylation events and (2) to develop mass spectrometry tools for the identification of non-canonical ubiquitylation on a proteomic scale. The expectation is that this research will produce a tangible expansion of our understanding of ubiquitin biology and, consequently, open up new opportunities for pharmacological intervention to treat human diseases in the future.

1. K. C. Pao et al., Nature. 2018. 556. 381-385

2. I. R. Kelsall et al., Proc Natl Acad Sci U S A. 2019. 116. 13293-13298

3. V. De Cesare et al., Proc Natl Acad Sci U S A. 2021. Jan 26; 118(4)