Variant RING finger, HC subclass (C4C4-type), found in RING finger protein 217 (RNF217) and similar proteins
RNF217, also known as IBR domain-containing protein 1 (IBRDC1), is a transmembrane (TM) domain-containing RBR-type E3 ubiquitin-protein ligase mainly expressed in testis and skeletal muscle, as different splice variants. It interacts with the anti-apoptotic protein HAX1, and is adjacent to a translocation breakpoint involving ETV6 in childhood acute lymphoblastic leukemia (ALL). RNF217 contains a RBR domain followed by TMs. The RBR domain was previously known as RING-BetweenRING-RING domain or TRIAD [two RING fingers and a DRIL (double RING finger linked)] domain. Based on current understanding of the structural biology of RBR ligases, the nomenclature of RBR has been corrected as RING-BRcat (benign-catalytic)-Rcat (required-for-catalysis) recently. The RBR (RING1-BRcat-Rcat) domain uses an auto-inhibitory mechanism to modulate ubiquitination activity, as well as a hybrid mechanism that combines aspects from both RING and HECT E3 ligase function to facilitate the ubiquitination reaction. This model corresponds to the RING domain, a variant C4C4-type RING finger whose overall folding is similar to that of the C3HC4-type RING-HC finger. It is required for RBR-mediated ubiquitination.
Comment:The C4C4-type RING finger of Homo sapiens RNF217 shows a partially new pattern, compared with the typical C4C4-type RING-HC finger. The fourth and eighth conserved Cys residues are in different positions.
Comment:consensus of the typical C3HC4-type RING-HC finger: C-X2-C-X(9-39)-C-X(1-3)-H-X(2-3)-C-X2-C-X(4-48)-C-X2-C, X is any amino acid and the number of X residues varies in different fingers.
Comment:A RING finger typically binds two zinc atoms, with its Cys and/or His side chains in a unique "cross-brace" arrangement.
Jiyao W et al.(2023). "The conserved domain database in 2023.",