title: The E3 ligase HOIP specifies linear ubiquitin chain assembly through its RING-IBR-RING domain and the unique LDD extension.
abstract: Activation of the NF-κB pathway requires the formation of Met1-linked 'linear' ubiquitin chains on NEMO, which is catalysed by the Linear Ubiquitin Chain Assembly Complex (LUBAC) E3 consisting of HOIP, HOIL-1L and Sharpin. Here, we show that both LUBAC catalytic activity and LUBAC specificity for linear ubiquitin chain formation are embedded within the RING-IBR-RING (RBR) ubiquitin ligase subunit HOIP. Linear ubiquitin chain formation by HOIP proceeds via a two-step mechanism involving both RING and HECT E3-type activities. RING1-IBR catalyses the transfer of ubiquitin from the E2 onto RING2, to transiently form a HECT-like covalent thioester intermediate. Next, the ubiquitin is transferred from HOIP onto the N-terminus of a target ubiquitin. This transfer is facilitated by a unique region in the C-terminus of HOIP that we termed 'Linear ubiquitin chain Determining Domain' (LDD), which may coordinate the acceptor ubiquitin. Consistent with this mechanism, the RING2-LDD region was found to be important for NF-κB activation in cellular assays. These data show how HOIP combines a general RBR ubiquitin ligase mechanism with unique, LDD-dependent specificity for producing linear ubiquitin chains.
authors.affiliation: Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Judith J
authors.initials: JJ
authors.lastname: Smit
authors.forename: Davide
authors.initials: D
authors.lastname: Monteferrario
authors.forename: Sylvie M
authors.initials: SM
authors.lastname: Noordermeer
authors.forename: Willem J
authors.initials: WJ
authors.lastname: van Dijk
authors.forename: Bert A
authors.initials: BA
authors.lastname: van der Reijden
authors.forename: Titia K
authors.initials: TK
authors.lastname: Sixma
mesh_terms: D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D016328:NF-kappa B / Q000378:metabolism; D017434:Protein Structure, Tertiary; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination / Q000502:physiology
chemical_list: D002352:Carrier Proteins; D016328:NF-kappa B; D025801:Ubiquitin; C558338:RNF31 protein, human; D044767:Ubiquitin-Protein Ligases