BRcat (benign-catalytic) and Rcat (required-for-catalysis) domains, part of the RBR (RING1-BRcat-Rcat) domain
The RBR family of RING-type E3 ligases are characterized by containing an RBR (RING1-BRcat-Rcat) domain, which was previously known as RING-BetweenRING-RING domain or TRIAD [two RING fingers and a DRIL (double RING finger linked)] domain. It is composed of an extended RING domain (RING1) followed by an in-between RING (IBR) domain and the catalytic domain, which is structurally an IBR domain but is commonly designated as RING2. Based on current understanding of the structural biology of RBR ligases, the nomenclature of RBRs has been changed to RING1-BRcat (benign-catalytic)-Rcat (required-for-catalysis), where the IBR and RING2 domains have been renamed as BRcat and Rcat domains, respectively. The RBR 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 functions to facilitate the ubiquitination reaction. The BRcat domain adopts the same fold as the Rcat domain while lacking the catalytic cysteine residue and ubiquitination activity. RBR family members play roles in protein quality control and can indirectly regulate transcription. Evidence suggests that RBR proteins are often parts of cullin-containing ubiquitin ligase complexes.
Comment:the BRcat domain binds two zinc ions while the Rcat domain can bind 2 to 3 zinc ions; each ion is coordinated by 4 amino acid ligands (Cys or His); only 6 coordinating amino acids are in the alignment
Structure:5EDV; Homo sapiens RNF31 binds two Zn2+ ions through its BRcat domain.
Structure:5EDV; Homo sapiens RNF31 binds three Zn2+ ions through its Rcat domain.
Jiyao W et al.(2023). "The conserved domain database in 2023.",