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Updated: Aug 15, 2026

In Vitro SUMOylation Assay to Study SUMO E3 Ligase Activity
Published on: January 29, 2018
A proline-90 residue unique to SUMO-4 prevents maturation and sumoylation
David Owerbach1, Eileen M McKay, Edward T H Yeh
1Molecular Diabetes and Metabolism Section and the Harry B. and Aileen B. Gordon Diabetes Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA. davido@bcm.tmc.edu
Abstract:
Four small ubiquitin-related modifier (SUMO) genes have been identified in humans. However, little is known about the basic biology of SUMO-4. Here, we report that SUMO-4 differs from SUMO-1, -2, and -3 in that the maturation process of SUMO-4 to active form containing C-terminal di-glycine residues is inhibited by a unique proline residue located at position 90 (Pro-90). Although, both the hydrolase and isopeptidase activities of SUMO peptidases are significantly diminished by Pro-90 as compared to Gln-90 (glutamine) in mutated SUMO genes, only the defective hydrolase activity appears to be biologically relevant. Native SUMO-4, thus, appears to be unable to form covalent isopeptide bonds with substrates. A biological role of SUMO-4, through non-covalent interactions is proposed.
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