SUMO-interacting Motif (SIM): Proteins and Enzymes

Small Ubiquitin-like Modifiers (SUMOs) are a family of small, related proteins that are enzymatically attached to target proteins by a process termed SUMOylation. This post-translational modification regulates many cellular processes including DNA transcription and repair, cell cycle progression, protein intracellular trafficking, and nuclear receptor activities. SUMO binding and/or interaction with proteins is mediated by short amino acid consensus sequences termed SUMO-interacting motifs (SIMs). To date, all SIMs appear to contain a hydrophobic core sequence that is either preceded or succeeded by an acidic region composed of either glutamate or aspartate residues or phosphorylated serine or threonine residues. The hydrophobic core of SIMs has been shown to interact with the alpha-helix and beta2-strand surfaces on SUMO proteins while the negatively charged residues surrounding the hydrophobic core appear to influence binding affinities and dictate binding preferences for the various SUMO isoforms. SIMs have been identified in numerous types of proteins including SUMO ligases (E3), transcription factors, and transcriptional repressors.