Rcat domain found in HOIL-1-interacting protein (HOIP) and similar proteins
HOIP, also called RING finger protein 31 (RNF31) or zinc in-between-RING-finger ubiquitin-associated domain protein, together with HOIL-1 and SHARPIN, forms the E3-ligase complex (also known as linear-ubiquitin-chain assembly complex LUBAC) that regulates NF-kappaB activity and apoptosis. It also interacts with the atypical mammalian orphan receptor DAX-1, trigger DAX-1 ubiquitination and stabilization, and participate in repressing steroidogenic gene expression. HOIP contains three Npl4 zinc fingers, a central ubiquitin-associated (UBA) domain responsible for the interaction with the N-terminal ubiquitin-like domain (UBL) of HOIL-1L, an RBR domain, and a C-terminal linear chain determining domain (LDD). 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 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 Rcat domain of HOIP that is essential for RBR E3 ligase activity and adopts the same fold as the BRcat domain.
Jiyao W et al.(2023). "The conserved domain database in 2023.",