5edv
From Proteopedia
Structure of the HOIP-RBR/UbcH5B~ubiquitin transfer complex
Structural highlights
FunctionRNF31_HUMAN E3 ubiquitin-protein ligase component of the LUBAC complex which conjugates linear ('M-1'-linked) polyubiquitin chains to substrates and plays a key role in NF-kappa-B activation and regulation of inflammation. LUBAC conjugates linear polyubiquitin to IKBKG and RIPK1 and is involved in activation of the canonical NF-kappa-B and the JNK signaling pathways. Linear ubiquitination mediated by the LUBAC complex interferes with TNF-induced cell death and thereby prevents inflammation. LUBAC is proposed to be recruited to the TNF-R1 signaling complex (TNF-RSC) following polyubiquitination of TNF-RSC components by BIRC2 and/or BIRC3 and to conjugate linear polyubiquitin to IKBKG and possibly other components contributing to the stability of the complex. Binds polyubiquitin of different linkage types.[1] [2] [3] [4] [5] [6] [7] Publication Abstract from PubMedUbiquitination is a central process affecting all facets of cellular signalling and function. A critical step in ubiquitination is the transfer of ubiquitin from an E2 ubiquitin-conjugating enzyme to a substrate or a growing ubiquitin chain, which is mediated by E3 ubiquitin ligases. RING-type E3 ligases typically facilitate the transfer of ubiquitin from the E2 directly to the substrate. The RING-between-RING (RBR) family of RING-type E3 ligases, however, breaks this paradigm by forming a covalent intermediate with ubiquitin similarly to HECT-type E3 ligases. The RBR family includes Parkin and HOIP, the central catalytic factor of the LUBAC (linear ubiquitin chain assembly complex). While structural insights into the RBR E3 ligases Parkin and HHARI in their overall auto-inhibited forms are available, no structures exist of intact fully active RBR E3 ligases or any of their complexes. Thus, the RBR mechanism of action has remained largely unknown. Here we present the first structure, to our knowledge, of the fully active human HOIP RBR in its transfer complex with an E2~ubiquitin conjugate, which elucidates the intricate nature of RBR E3 ligases. The active HOIP RBR adopts a conformation markedly different from that of auto-inhibited RBRs. HOIP RBR binds the E2~ubiquitin conjugate in an elongated fashion, with the E2 and E3 catalytic centres ideally aligned for ubiquitin transfer, which structurally both requires and enables a HECT-like mechanism. In addition, three distinct helix-IBR-fold motifs inherent to RBRs form ubiquitin-binding regions that engage the activated ubiquitin of the E2~ubiquitin conjugate and, surprisingly, an additional regulatory ubiquitin molecule. The features uncovered reveal critical states of the HOIP RBR E3 ligase cycle, and comparison with Parkin and HHARI suggests a general mechanism for RBR E3 ligases. Structure of a HOIP/E2~ubiquitin complex reveals RBR E3 ligase mechanism and regulation.,Lechtenberg BC, Rajput A, Sanishvili R, Dobaczewska MK, Ware CF, Mace PD, Riedl SJ Nature. 2016 Jan 28;529(7587):546-50. doi: 10.1038/nature16511. Epub 2016 Jan 20. PMID:26789245[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See Also
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