TRIM21: Proteins and Enzymes

TRIM21 (Tripartite motif-containing protein 21; also Ro(SS-A), 52 kDa Ro Protein/Ro52, and RING finger protein 81) is a 52-56 kDa member of the RING finger B box coiled coil family of proteins. It is an E3 ligase that is found in both nucleus and cytoplasm, where it is often associated with microtubules. TRIM21 ubiquitinates select proteins. In B cells, it targets the Fc fragment of misfolded IgG, providing QC on its production. In macrophages, it acts in a nondegradative manner on IRF8, promoting innate immunity. Human TRIM21 is 475 amino acids (aa) in length and contains one E3 ligase RING finger domain (aa 16-55), a B Box type zinc finger region (aa 92-123), a coiled coil region (aa 128-238) and a C-terminal SPRY/B30.2 Ig binding domain (aa 268-465). TRIM21 is reported to form trimers. Over aa 195-293, human TRIM21 exhibits 72% aa identity with mouse TRIM21.