E3 ubiquitin-protein ligase TRIM21 (TRIM21)

E3 ubiquitin-protein ligase whose activity is dependent on E2 enzymes, UBE2D1, UBE2D2, UBE2E1 and UBE2E2. Types a ubiquitin ligase complex in cooperation with the E2 UBE2D2 that's used not only for the ubiquitination of USP4 and IKBKB but also because of its self-ubiquitination.

Part of cullin-RING-based SCF (SKP1-CUL1-F-box protein) E3 ubiquitin-protein ligase complexes such as SCF(SKP2)-like complexes. A TRIM21-containing SCF(SKP2)- like complex is shown to mediate ubiquitination of CDKN1B ('Thr- 187' phosphorylated-form), thereby promoting its degradation by the proteasome.