SUMO1
SUMO1, historically named PIC1, is the founding member of the small ubiquitin-like modifier family and shares the ubiquitin beta-grasp fold despite limited sequence identity. After SENP proteases expose its C-terminal diglycine motif, the UBA1/SAE2 E1 and UBE2I E2 cascade conjugates SUMO1 to lysines within PsiKxE consensus motifs on nuclear and cytoplasmic targets such as PML and RanGAP1. Because SUMO1 lacks the internal acceptor site present in SUMO2/3, it typically caps poly-SUMO chains rather than extending them, modulating chain-dependent reader recruitment. SUMO1 modification controls nucleocytoplasmic transport, transcription, DNA repair, and mitotic progression, and its dysregulation is implicated in cancer and neurodegeneration.
