Abstract
BackgroundModification of proteins by the small ubiquitin like modifier (SUMO) is an essential process in mammalian cells. SUMO is covalently attached to lysines in target proteins via an enzymatic cascade which consists of E1 and E2, SUMO activating and conjugating enzymes. There is also a variable requirement for non-enzymatic E3 adapter like proteins, which can increase the efficiency and specificity of the sumoylation process. In addition to covalent attachment of SUMO to target proteins, specific non-covalent SUMO interaction motifs (SIMs) that are generally short hydrophobic peptide motifs have been identified.Methodology/Principal FindingsIntriguingly, consensus SIMs are present in most SUMO E3s, including the polycomb protein, Pc2/Cbx4. However, a role for SIMs in SUMO E3 activity remains to be shown. We show that Pc2 contains two functional SIMs, both of which contribute to full E3 activity in mammalian cells, and are also required for sumoylation of Pc2 itself. Pc2 forms distinct sub-nuclear foci, termed polycomb bodies, and can recruit partner proteins, such as the corepressor CtBP. We demonstrate that mutation of the SIMs in Pc2 prevents Pc2-dependent CtBP sumoylation, and decreases enrichment of SUMO1 and SUMO2 at polycomb foci. Furthermore, mutational analysis of both SUMO1 and SUMO2 reveals that the SIM-interacting residues of both SUMO isoforms are required for Pc2-mediated sumoylation and localization to polycomb foci.Conclusions/SignificanceThis work provides the first clear evidence for a role for SIMs in SUMO E3 activity.
Highlights
Covalent modification of proteins by small ubiquitin like modifier (SUMO) is an essential process in mammals, as evidenced by the embryonic lethality of mouse mutants lacking the SUMO conjugating enzyme, Ubc9 [1]
The wild type Pc2 fusion bound to both SUMO1 and SUMO2, whereas deletion of either SIM1 or SIM2 alone clearly decreased the interaction with both SUMO1 and SUMO2. It appears that Pc2 is capable of interacting directly with SUMO1 and SUMO2, and that the consensus SUMO interaction motifs (SIMs) in Pc2 are required for this interaction
Consistent with this we show the SIM-interacting domains of both SUMO1 and SUMO2 are required for Pc2dependent sumoylation of CtBP, but are dispensable when sumoylation is driven by high levels of Ubc9
Summary
Covalent modification of proteins by SUMO is an essential process in mammals, as evidenced by the embryonic lethality of mouse mutants lacking the SUMO conjugating enzyme, Ubc9 [1]. SUMO is covalently attached to lysine residues within the target protein, in the majority of cases SUMO is attached to a lysine within the yKxE consensus site (where y is hydrophobic and x is any residue) [8,9]. SUMO-loaded Ubc can modify substrate proteins directly, resulting in the covalent attachment of SUMO to the acceptor lysine. SUMO is covalently attached to lysines in target proteins via an enzymatic cascade which consists of E1 and E2, SUMO activating and conjugating enzymes. In addition to covalent attachment of SUMO to target proteins, specific non-covalent SUMO interaction motifs (SIMs) that are generally short hydrophobic peptide motifs have been identified
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
