Identification of MK2 SUMOylation sites. (A) Diagram of MK2 protein structure showing a possible SUMOylation site identified by Abgent's SUMOplot software. The lysine-339 (K339) residue was identified with a score of 0.93. (B) MK2 SUMOylation at K339 was demonstrated in CHO cells expressing Flag-tagged WT-MK2, HA-tagged SUMO3, and the SUMO E2 ligase Ubc9. MK2 SUMOylation was detected by immunoprecipitating Flag-tagged MK2, followed by immunoblotting for HA-tagged SUMO3. Note the greatly reduced SUMOylation for the K339R MK2 mutant protein (lane 4). Also note that no SUMOylation occurred without Ubc9 expression. (B) Representative images from 1 of 3 independent experiments are shown (n = 3).