TRIM21

Tripartite motif-containing protein 21 also known as E3 ubiquitin-protein ligase TRIM21 is a is_associated_with::protein that in humans is encoded by the TRIM21 is_associated_with::gene. Alternatively spliced transcript variants for this gene have been described but the full-length nature of only one has been determined. It is expressed in most human tissues.

Structure
TRIM21 is a member of the tripartite motif (TRIM) family. The TRIM motif includes three zinc-binding domains, a is_associated_with::RING finger domain, a B-box type 1 and a B-box type 2 is_associated_with::zinc finger, and a is_associated_with::coiled coil region.

Function
TRIM21 is an intracellular antibody effector in the is_associated_with::intracellular antibody-mediated proteolysis pathway. It binds to is_associated_with::immunoglobulin G as well as is_associated_with::immunoglobulin M on antibody marked non-enveloped virions which have infected the cell. Either by autoubiquitination or by ubiquitination of a cofactor, it is then responsible for directing the virions to the is_associated_with::proteasome. TRIM21 itself is not degraded in the proteasome unlike both the viral capsid and the bound antibody.

TRIM21 is part of the RoSSA ribonucleoprotein, which includes a single polypeptide and one of four small RNA molecules. The RoSSA particle localizes to both the cytoplasm and the nucleus.

Clinical significance
RoSSA interacts with autoantigens in patients with is_associated_with::Sjögren's syndrome and is_associated_with::systemic lupus erythematosus.