Chemical protein synthesis combined with protein cell delivery reveals new insights on the maturation process of SUMO2.

The Small Ubiquitin-like Modifier (SUMO) is a crucial post-translational modifier of proteins, playing a key role in various cellular functions. All SUMOs are synthesized as precursor proteins that must be proteolytically processed. However, the maturation process of cleaving the extending C-terminal tail, preceding SUMOylation of substrates, remains poorly understood, especially within cellular environments. Chemical protein synthesis coupled with cell delivery offers great opportunities to prepare SUMO analogues to investigate this process and in live cells. Applying this unique combination we show that SUMO2 analogues containing the native tail undergo rapid cleavage and nuclear localisation, while a Gly93Ala mutation impairs cleavage and alters localisation. Tail mutations (Val94Glu, Tyr95Ala) affected cleavage rates, highlighting roles in SUMO-SENP protease interactions. In cells, SUMO2 analogues containing tail mutations underwent cleavage and subsequently incorporated into promyelocytic leukemia nuclear bodies (PML-NBs). These findings advance our understanding of SUMO2 maturation and provide a foundation for future studies of this process for different SUMO paralogues in various cell lines and tissues.