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U-box domain, a modified RING finger The U-box protein family is a family of E3 enzymes that also includes the HECT family and the RING finger family. The E3 enzyme is ubiquitin-protein ligase that cooperates with a ubiquitin-activating enzyme (E1) and a ubiquitin-conjugating enzyme (E2), and plays a central role in determining the specificity of the ubiquitination system. It removes the ubiquitin molecule from the E2 enzyme and attaches it to the target substrate, forming a covalent bond between ubiquitin and the target. U-box proteins are characterized by the presence of a U-box domain of approximately 70 amino acids. The U-box is a modified form of the RING finger domain that lacks metal chelating cysteines and histidines. It resembles the cross-brace RING structure consisting of three beta-sheets and a single alpha-helix, which would be stabilized by salt bridges instead of chelated metal ions. U-box proteins are widely distributed among eukaryotic organisms and show a higher prevalence in plants than in other organisms. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",