TRIM21

TRIM21, or Tripartite Motif-Containing 21, also known as Ro52 or Ssa1, is a member of the tripartite motif protein family and primarily functions within cells.
The mechanism of action of TRIM21 involves its function as an E3 ubiquitin ligase, which relies on E2 enzymes such as UBE2D1, UBE2D2, UBE2E1, and UBE2E2. It forms a ubiquitin ligase complex with UBE2D2, ubiquitinating USP4, IKBKB, and itself. TRIM21 is also associated with the cullin-RING-based SCF E3 ligase complex, mediating the ubiquitination of CDKN1B. As an intracellular antibody effector, TRIM21 plays a role in the intracellular antibody-mediated protein degradation pathway, recognizing the Fc domain and binding to antibody-tagged non-enveloped viruses, guiding them to the proteasome for degradation through self-ubiquitination or ubiquitination of auxiliary factors. Additionally, TRIM21 is involved in the innate immune response, positively or negatively regulating antiviral responses by affecting intracellular PRR-mediated signaling.
Abnormalities in the function of TRIM21 are associated with various autoimmune diseases, such as systemic lupus erythematosus.