Protein Cousins: Characterizing Ubiquitin-Like Proteins within the Ubiquitin Code

Ubiquitin-like proteins (UBLs) are a group of small proteins that share sequence homology with ubiquitin. Although structurally like ubiquitin, UBLs are a protein group that play a distinct role in biological signaling ranging from DNA repair to cellular inflammatory response. The group achieves this by participating in enzymatic cascades that are intricately adjacent to that of the ubiquitin-proteasome machinery yet remain functionally distinct. Due to the unique duality of UBLs, researchers over the past three decades have sought to answer the fundamental question: Do the conjugation machinery of both protein classes overlap, and if so, which specific enzymes mediate such interaction? E2 ubiquitin-conjugating enzymes are one place of overlap in which overlaps exist. Often referred to as the “middlemen,” E2s play a crucial role in the ubiquitin cascade by facilitating the transfer of activated ubiquitin to protein substrates, in collaboration with ubiquitin ligases (E3s). Through extensive research, these same enzymes have also been shown to conjugate specific UBLs, facilitating their attachment to protein substrates in a manner like ubiquitin. Despite such findings, there is still a gap in understanding how E2s mediate the interplay between both cascades. Consequently, the drive to deepen our understanding of how UBLs interact with E2s is compelling, as it offers a clearer insight into how these protein families converge within the broader context of cellular function and disease. This project aims to characterize nine UBLs and one Ub variant through a series of biochemical assays to elucidate their interactions with E2s.