BRcat domain found in F-box only protein 43 (FBXO43)
FBXO43, also called FBX43 or endogenous meiotic inhibitor 2 (EMI2), plays a key role during the meiotic cell cycle. It is required to establish and maintain the arrest of oocytes at the second meiotic metaphase until fertilization. It probably acts by inhibiting the anaphase-promoting complex/cyclosome (APC/C) ubiquitin ligase. It may recognize and bind to some phosphorylated proteins and promotes their ubiquitination and degradation. FBXO43 contains an F-box domain, and the first half of the RBR domain that 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 changed to RING1-BRcat (benign-catalytic)-Rcat (required-for-catalysis) recently. 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. This model corresponds to the BRcat (benign-catalytic) domain that adopts the same fold as the Rcat domain while lacking the catalytic cysteine residue and ubiquitination activity.
Jiyao W et al.(2023). "The conserved domain database in 2023.",