RING finger, HC subclass, found in tripartite motif-containing proteins, TRIM4, TRIM75, tripartite motif family-like protein 1 (TRIML1) and similar proteins
TRIM4 and TRIM75, two closely related tripartite motif-containing proteins, belong to the C-IV subclass of TRIM (tripartite motif) family of proteins that are defined by their N-terminal RBCC (RING, Bbox, and coiled coil) domains, including three consecutive zinc-binding domains, a C3HC4-type RING-HC finger, Bbox1 and Bbox2, and a coiled coil region, as well as a SPRY/B30.2 domain positioned C-terminal to the RBCC domain. TRIM4, also known as RING finger protein 87 (RNF87), is a cytoplasmic E3 ubiquitin-protein ligase that it had recently evolved and is present only in higher mammals. It transiently interacts with mitochondria, induces mitochondrial aggregation and sensitizes the cells to hydrogen peroxide (H2O2) induced death. Its interaction with peroxiredoxin 1 (PRX1) is critical for the regulation of H2O2 induced cell death. Moreover, TRIM4 functions as a positive regulator of RIG-I-mediated type I interferon induction. It regulates the K63-linked ubiquitination of RIG-1 and assembly of antiviral signaling complex at mitochondria. TRIM75 mainly localizes within spindles, suggesting it may function in spindle organization and thereby affect meiosis. The family also includes TRIML1 that is identical to TRIM11 and TRIM17 except for the absence of B-box domain. TRIML1, also known as RING finger protein 209 (RNF209), is a probable E3 ubiquitin-protein ligase expressed in embryo before implantation. It plays an important role in blastocyst development. By interacting with USP5 (also known as isoT), TRIML1 may exerts its influence on debranching ubiquitin from multi-chains on the stability and activity of protein substrates in the preimplantation embryo.