1
|
Purser N, Tripathi-Giesgen I, Li J, Scott DC, Horn-Ghetko D, Baek K, Schulman BA, Alpi AF, Kleiger G. Catalysis of non-canonical protein ubiquitylation by the ARIH1 ubiquitin ligase. Biochem J 2023; 480:1817-1831. [PMID: 37870100 PMCID: PMC10657180 DOI: 10.1042/bcj20230373] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Revised: 10/19/2023] [Accepted: 10/23/2023] [Indexed: 10/24/2023]
Abstract
Protein ubiquitylation typically involves isopeptide bond formation between the C-terminus of ubiquitin to the side-chain amino group on Lys residues. However, several ubiquitin ligases (E3s) have recently been identified that ubiquitylate proteins on non-Lys residues. For instance, HOIL-1 belongs to the RING-in-between RING (RBR) class of E3s and has an established role in Ser ubiquitylation. Given the homology between HOIL-1 and ARIH1, an RBR E3 that functions with the large superfamily of cullin-RING E3 ligases (CRLs), a biochemical investigation was undertaken, showing ARIH1 catalyzes Ser ubiquitylation to CRL-bound substrates. However, the efficiency of ubiquitylation was exquisitely dependent on the location and chemical environment of the Ser residue within the primary structure of the substrate. Comprehensive mutagenesis of the ARIH1 Rcat domain identified residues whose mutation severely impacted both oxyester and isopeptide bond formation at the preferred site for Ser ubiquitylation while only modestly affecting Lys ubiquitylation at the physiological site. The results reveal dual isopeptide and oxyester protein ubiquitylation activities of ARIH1 and set the stage for physiological investigations into this function of emerging importance.
Collapse
Affiliation(s)
- Nicholas Purser
- Department of Chemistry and Biochemistry, University of Nevada, Las Vegas, Las Vegas, NV, U.S.A
| | - Ishita Tripathi-Giesgen
- Department of Molecular Machines and Signaling, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Jerry Li
- Department of Chemistry and Biochemistry, University of Nevada, Las Vegas, Las Vegas, NV, U.S.A
| | - Daniel C. Scott
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, U.S.A
| | - Daniel Horn-Ghetko
- Department of Molecular Machines and Signaling, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Kheewoong Baek
- Department of Molecular Machines and Signaling, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Brenda A. Schulman
- Department of Molecular Machines and Signaling, Max Planck Institute of Biochemistry, Martinsried, Germany
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, U.S.A
| | - Arno F. Alpi
- Department of Molecular Machines and Signaling, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Gary Kleiger
- Department of Chemistry and Biochemistry, University of Nevada, Las Vegas, Las Vegas, NV, U.S.A
| |
Collapse
|
2
|
Reiter KH, Zelter A, Janowska MK, Riffle M, Shulman N, MacLean BX, Tamura K, Chambers MC, MacCoss MJ, Davis TN, Guttman M, Brzovic PS, Klevit RE. Cullin-independent recognition of HHARI substrates by a dynamic RBR catalytic domain. Structure 2022; 30:1269-1284.e6. [PMID: 35716664 PMCID: PMC9444911 DOI: 10.1016/j.str.2022.05.017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2022] [Revised: 04/15/2022] [Accepted: 05/24/2022] [Indexed: 11/27/2022]
Abstract
RING-between-RING (RBR) E3 ligases mediate ubiquitin transfer through an obligate E3-ubiquitin thioester intermediate prior to substrate ubiquitination. Although RBRs share a conserved catalytic module, substrate recruitment mechanisms remain enigmatic, and the relevant domains have yet to be identified for any member of the class. Here we characterize the interaction between the auto-inhibited RBR, HHARI (AriH1), and its target protein, 4EHP, using a combination of XL-MS, HDX-MS, NMR, and biochemical studies. The results show that (1) a di-aromatic surface on the catalytic HHARI Rcat domain forms a binding platform for substrates and (2) a phosphomimetic mutation on the auto-inhibitory Ariadne domain of HHARI promotes release and reorientation of Rcat for transthiolation and substrate modification. The findings identify a direct binding interaction between a RING-between-RING ligase and its substrate and suggest a general model for RBR substrate recognition.
Collapse
Affiliation(s)
- Katherine H Reiter
- Department of Biochemistry, University of Washington, Seattle, WA 98195, USA
| | - Alex Zelter
- Department of Biochemistry, University of Washington, Seattle, WA 98195, USA
| | - Maria K Janowska
- Department of Biochemistry, University of Washington, Seattle, WA 98195, USA
| | - Michael Riffle
- Department of Biochemistry, University of Washington, Seattle, WA 98195, USA
| | - Nicholas Shulman
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Brendan X MacLean
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Kaipo Tamura
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Matthew C Chambers
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Michael J MacCoss
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Trisha N Davis
- Department of Biochemistry, University of Washington, Seattle, WA 98195, USA
| | - Miklos Guttman
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Peter S Brzovic
- Department of Biochemistry, University of Washington, Seattle, WA 98195, USA
| | - Rachel E Klevit
- Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.
| |
Collapse
|
3
|
Dove KK, Klevit RE. RING-Between-RING E3 Ligases: Emerging Themes amid the Variations. J Mol Biol 2017; 429:3363-3375. [PMID: 28827147 DOI: 10.1016/j.jmb.2017.08.008] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Revised: 08/09/2017] [Accepted: 08/10/2017] [Indexed: 11/30/2022]
Abstract
Covalent, reversible, post-translational modification of cellular proteins with the small modifier, ubiquitin (Ub), regulates virtually every known cellular process in eukaryotes. The process is carried out by a trio of enzymes: a Ub-activating (E1) enzyme, a Ub-conjugating (E2) enzyme, and a Ub ligase (E3) enzyme. RING-in-Between-RING (RBR) E3s constitute one of three classes of E3 ligases and are defined by a RING-HECT-hybrid mechanism that utilizes a E2-binding RING domain and a second domain (called RING2) that contains an active site Cys required for the formation of an obligatory E3~Ub intermediate. Albeit a small class, RBR E3s in humans regulate diverse cellular process. This review focuses on non-Parkin members such as HOIP/HOIL-1L (the only E3s known to generate linear Ub chains), HHARI and TRIAD1, both of which have been recently demonstrated to work together with Cullin RING E3 ligases. We provide a brief historical background and highlight, summarize, and discuss recent developments in the young field of RBR E3s. Insights reviewed here include new understandings of the RBR Ub-transfer mechanism, specifically the role of RING1 and various Ub-binding sites, brief structural comparisons among members, and different modes of auto-inhibition and activation.
Collapse
Affiliation(s)
- Katja K Dove
- Department of Biochemistry, University of Washington, Seattle, WA, United States
| | - Rachel E Klevit
- Department of Biochemistry, University of Washington, Seattle, WA, United States.
| |
Collapse
|
4
|
Structural insights into the mechanism and E2 specificity of the RBR E3 ubiquitin ligase HHARI. Nat Commun 2017; 8:211. [PMID: 28790309 PMCID: PMC5548887 DOI: 10.1038/s41467-017-00272-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Accepted: 06/15/2017] [Indexed: 12/19/2022] Open
Abstract
RING-in-between-RING (RBR) ubiquitin (Ub) E3 ligases function with Ub E2s through a RING/HECT hybrid mechanism to conjugate Ub to target proteins. Here, we report the crystal structure of the RBR E3, HHARI, in complex with a UbcH7 ~ Ub thioester mimetic which reveals the molecular basis for the specificity of this cognate E2/RBR E3 pair. The structure also reveals mechanistically important conformational changes in the RING1 and UBA-like domains of HHARI that accompany UbcH7 ~ Ub binding and provides a molecular basis by which HHARI recruits E2 ~ Ub in an ‘open’ conformation. In addition to optimally functioning with an E2 that solely performs transthiolation, our data suggests that HHARI prevents spurious discharge of Ub from E2 to lysine residues by: (1) harboring structural elements that block E2 ~ Ub from adopting a ‘closed’ conformation and (2) participating in contacts to ubiquitin that promote an open E2 ~ Ub conformation. HHARI is a RING-in-between-RING (RBR) ubiquitin (Ub) E3 ligase. Here the authors present the crystal structure of HHARI with the UbcH7 ~ Ub thioester intermediate mimetic, which reveals that HHARI binds this E2 ~ Ub in an open conformation and explains the specificity of this cognate RBR E3/E2 pair.
Collapse
|
5
|
Abstract
Post-translational modification (PTM) of proteins by ubiquitination is an essential cellular regulatory process. Such regulation drives the cell cycle and cell division, signalling and secretory pathways, DNA replication and repair processes and protein quality control and degradation pathways. A huge range of ubiquitin signals can be generated depending on the specificity and catalytic activity of the enzymes required for attachment of ubiquitin to a given target. As a consequence of its importance to eukaryotic life, dysfunction in the ubiquitin system leads to many disease states, including cancers and neurodegeneration. This review takes a retrospective look at our progress in understanding the molecular mechanisms that govern the specificity of ubiquitin conjugation.
Collapse
|
6
|
Buetow L, Huang DT. Structural insights into the catalysis and regulation of E3 ubiquitin ligases. Nat Rev Mol Cell Biol 2016; 17:626-42. [PMID: 27485899 PMCID: PMC6211636 DOI: 10.1038/nrm.2016.91] [Citation(s) in RCA: 408] [Impact Index Per Article: 51.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Covalent attachment (conjugation) of one or more ubiquitin molecules to protein substrates governs numerous eukaryotic cellular processes, including apoptosis, cell division and immune responses. Ubiquitylation was originally associated with protein degradation, but it is now clear that ubiquitylation also mediates processes such as protein-protein interactions and cell signalling depending on the type of ubiquitin conjugation. Ubiquitin ligases (E3s) catalyse the final step of ubiquitin conjugation by transferring ubiquitin from ubiquitin-conjugating enzymes (E2s) to substrates. In humans, more than 600 E3s contribute to determining the fates of thousands of substrates; hence, E3s need to be tightly regulated to ensure accurate substrate ubiquitylation. Recent findings illustrate how E3s function on a structural level and how they coordinate with E2s and substrates to meticulously conjugate ubiquitin. Insights regarding the mechanisms of E3 regulation, including structural aspects of their autoinhibition and activation are also emerging.
Collapse
Affiliation(s)
- Lori Buetow
- The Beatson Institute for Cancer Research, Garscube Estate, Switchback Road, Glasgow, G61 1BD, United Kingdom
| | - Danny T. Huang
- The Beatson Institute for Cancer Research, Garscube Estate, Switchback Road, Glasgow, G61 1BD, United Kingdom
| |
Collapse
|
7
|
Wright JD, Mace PD, Day CL. Noncovalent Ubiquitin Interactions Regulate the Catalytic Activity of Ubiquitin Writers. Trends Biochem Sci 2016; 41:924-937. [PMID: 27614784 DOI: 10.1016/j.tibs.2016.08.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Revised: 07/26/2016] [Accepted: 08/01/2016] [Indexed: 11/27/2022]
Abstract
Covalent modification of substrate proteins with ubiquitin is the end result of an intricate network of protein-protein interactions. The inherent ability of the E1, E2, and E3 proteins of the ubiquitylation cascade (the ubiquitin writers) to interact with ubiquitin facilitates this process. Importantly, contact between ubiquitin and the E2/E3 writers is required for catalysis and the assembly of chains of a given linkage. However, ubiquitin is also an activator of ubiquitin-writing enzymes, with many recent studies highlighting the ability of ubiquitin to regulate activity and substrate modification. Here, we review the interactions between ubiquitin-writing enzymes and regulatory ubiquitin molecules that promote activity, and highlight the potential of these interactions to promote processive ubiquitin transfer.
Collapse
Affiliation(s)
- Joshua D Wright
- Department of Biochemistry, University of Otago, Dunedin 9054, New Zealand; The Francis Crick Institute, London NW1 1AT, UK
| | - Peter D Mace
- Department of Biochemistry, University of Otago, Dunedin 9054, New Zealand
| | - Catherine L Day
- Department of Biochemistry, University of Otago, Dunedin 9054, New Zealand.
| |
Collapse
|
8
|
Dove KK, Stieglitz B, Duncan ED, Rittinger K, Klevit RE. Molecular insights into RBR E3 ligase ubiquitin transfer mechanisms. EMBO Rep 2016; 17:1221-35. [PMID: 27312108 PMCID: PMC4967960 DOI: 10.15252/embr.201642641] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Accepted: 05/24/2016] [Indexed: 12/30/2022] Open
Abstract
RING-in-between-RING (RBR) ubiquitin (Ub) ligases are a distinct class of E3s, defined by a RING1 domain that binds E2 Ub-conjugating enzyme and a RING2 domain that contains an active site cysteine similar to HECT-type E3s. Proposed to function as RING/HECT hybrids, details regarding the Ub transfer mechanism used by RBRs have yet to be defined. When paired with RING-type E3s, E2s perform the final step of Ub ligation to a substrate. In contrast, when paired with RBR E3s, E2s must transfer Ub onto the E3 to generate a E3~Ub intermediate. We show that RBRs utilize two strategies to ensure transfer of Ub from the E2 onto the E3 active site. First, RING1 domains of HHARI and RNF144 promote open E2~Ubs. Second, we identify a Ub-binding site on HHARI RING2 important for its recruitment to RING1-bound E2~Ub. Mutations that ablate Ub binding to HHARI RING2 also decrease RBR ligase activity, consistent with RING2 recruitment being a critical step for the RBR Ub transfer mechanism. Finally, we demonstrate that the mechanism defined here is utilized by a variety of RBRs.
Collapse
Affiliation(s)
- Katja K Dove
- Department of BiochemistryUniversity of WashingtonSeattleWAUSA
| | - Benjamin Stieglitz
- Mill Hill LaboratoryThe Francis Crick InstituteLondonUK,Present address: Department of Chemistry and BiochemistrySchool of Biological and Chemical SciencesQueen Mary University of LondonLondonUK
| | - Emily D Duncan
- Department of BiochemistryUniversity of WashingtonSeattleWAUSA
| | | | - Rachel E Klevit
- Department of BiochemistryUniversity of WashingtonSeattleWAUSA
| |
Collapse
|
9
|
Lechtenberg BC, Rajput A, Sanishvili R, Dobaczewska MK, Ware CF, Mace PD, Riedl SJ. Structure of a HOIP/E2~ubiquitin complex reveals RBR E3 ligase mechanism and regulation. Nature 2016; 529:546-50. [PMID: 26789245 PMCID: PMC4856479 DOI: 10.1038/nature16511] [Citation(s) in RCA: 120] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2015] [Accepted: 12/03/2015] [Indexed: 02/07/2023]
Abstract
Ubiquitination is a central process affecting all facets of cellular signaling and function1. 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 substrate2,3. The RBR family of RING-type E3 ligases, however, breaks this paradigm by forming a covalent intermediate with ubiquitin similarly to HECT-type E3 ligases4–6. The RBR family includes Parkin4 and HOIP, the central catalytic factor of the linear ubiquitin chain assembly complex (LUBAC)7. While structural insights into the RBR E3 ligases Parkin and HHARI in their overall autoinhibited forms are available8–13, no structures exist of intact fully active RBR E3 ligases or any of their complexes. Thus, the RBR mechanism of action has remained largely enigmatic. Here we present the first structure of the fully active 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 autoinhibited RBRs. HOIP-RBR binds the E2~ubiquitin conjugate in an elongated fashion, with the E2 and E3 catalytic centers ideally aligned for ubiquitin transfer, which structurally both requires and enables a HECT-like mechanism. In addition, surprisingly, three distinct helix–IBR-fold motifs inherent to RBRs form ubiquitin-binding regions that engage the activated ubiquitin of the E2~Ub conjugate as well as 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.
Collapse
Affiliation(s)
- Bernhard C Lechtenberg
- NCI-Designated Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Akhil Rajput
- Infectious and Inflammatory Disease Center, Sanford Burnham Prebys Medical Discovery Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Ruslan Sanishvili
- X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, USA
| | - Małgorzata K Dobaczewska
- NCI-Designated Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Carl F Ware
- Infectious and Inflammatory Disease Center, Sanford Burnham Prebys Medical Discovery Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Peter D Mace
- Biochemistry Department, University of Otago, 710 Cumberland Street, Dunedin 9054, New Zealand
| | - Stefan J Riedl
- NCI-Designated Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
| |
Collapse
|
10
|
Xie L, Lang-Mladek C, Richter J, Nigam N, Hauser MT. UV-B induction of the E3 ligase ARIADNE12 depends on CONSTITUTIVELY PHOTOMORPHOGENIC 1. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2015; 93:18-28. [PMID: 25817546 PMCID: PMC4503874 DOI: 10.1016/j.plaphy.2015.03.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2014] [Accepted: 03/20/2015] [Indexed: 05/05/2023]
Abstract
The UV-B inducible ARIADNE12 (ARI12) gene of Arabidopsis thaliana is a member of the RING-between-RING (RBR) family of E3 ubiquitin ligases for which a novel ubiquitination mechanism was identified in mammalian homologs. This RING-HECT hybrid mechanism needs a conserved cysteine which is replaced by serine in ARI12 and might affect the E3 ubiquitin ligase activity. We have shown that under photomorphogenic UV-B, ARI12 is a downstream target of the classical ultraviolet B (UV-B) UV Resistance Locus 8 (UVR8) pathway. However, under high fluence rate of UV-B ARI12 was induced independently of UVR8 and the UV-A/blue light and red/far-red photoreceptors. A key component of several light signaling pathways is Constitutively Photomorphogenic 1 (COP1). Upon UV-B COP1 is trapped in the nucleus through interaction with UVR8 permitting the activation of genes that regulate the biosynthesis of UV-B protective metabolites and growth adaptations. To clarify the role of COP1 in the regulation of ARI12 mRNA expression and ARI12 protein stability, localization and interaction with COP1 was assessed with and without UV-B. We found that COP1 controls ARI12 in white light, low and high fluence rate of UV-B. Furthermore we show that ARI12 is indeed an E3 ubiquitin ligase which is mono-ubiquitinated, a prerequisite for the RING-HECT hybrid mechanism. Finally, genetic analyses with transgenes expressing a genomic pmARI12:ARI12-GFP construct confirm the epistatic interaction between COP1 and ARI12 in growth responses to high fluence rate UV-B.
Collapse
Affiliation(s)
- Lisi Xie
- Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, Vienna, Austria.
| | - Christina Lang-Mladek
- Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, Vienna, Austria.
| | - Julia Richter
- Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, Vienna, Austria.
| | - Neha Nigam
- Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, Vienna, Austria.
| | - Marie-Theres Hauser
- Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, Vienna, Austria.
| |
Collapse
|
11
|
Mattiroli F, Sixma TK. Lysine-targeting specificity in ubiquitin and ubiquitin-like modification pathways. Nat Struct Mol Biol 2014; 21:308-16. [PMID: 24699079 DOI: 10.1038/nsmb.2792] [Citation(s) in RCA: 108] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2013] [Accepted: 02/13/2014] [Indexed: 12/19/2022]
Abstract
Ubiquitin and ubiquitin-like modifications are central to virtually all cellular signaling pathways. They occur primarily on lysine residues of target proteins and stimulate a large number of downstream signals. The diversity of these signals depends on the type, location and dynamics of the modification, but the role of the exact site of modification and the selectivity for specific lysines are poorly understood. Here we review the current literature on lysine specificity in these modifications, and we highlight the known signaling mechanisms and the open questions that pose future challenges to ubiquitin research.
Collapse
Affiliation(s)
- Francesca Mattiroli
- 1] Division of Biochemistry, Cancer Genomics Center, Netherlands Cancer Institute, Amsterdam, The Netherlands. [2]
| | - Titia K Sixma
- Division of Biochemistry, Cancer Genomics Center, Netherlands Cancer Institute, Amsterdam, The Netherlands
| |
Collapse
|
12
|
Abstract
The RBR (RING-BetweenRING-RING) or TRIAD [two RING fingers and a DRIL (double RING finger linked)] E3 ubiquitin ligases comprise a group of 12 complex multidomain enzymes. This unique family of E3 ligases includes parkin, whose dysfunction is linked to the pathogenesis of early-onset Parkinson's disease, and HOIP (HOIL-1-interacting protein) and HOIL-1 (haem-oxidized IRP2 ubiquitin ligase 1), members of the LUBAC (linear ubiquitin chain assembly complex). The RBR E3 ligases share common features with both the larger RING and HECT (homologous with E6-associated protein C-terminus) E3 ligase families, directly catalysing ubiquitin transfer from an intrinsic catalytic cysteine housed in the C-terminal domain, as well as recruiting thioester-bound E2 enzymes via a RING domain. Recent three-dimensional structures and biochemical findings of the RBRs have revealed novel protein domain folds not previously envisioned and some surprising modes of regulation that have raised many questions. This has required renaming two of the domains in the RBR E3 ligases to more accurately reflect their structures and functions: the C-terminal Rcat (required-for-catalysis) domain, essential for catalytic activity, and a central BRcat (benign-catalytic) domain that adopts the same fold as the Rcat, but lacks a catalytic cysteine residue and ubiquitination activity. The present review discusses how three-dimensional structures of RBR (RING1-BRcat-Rcat) E3 ligases have provided new insights into our understanding of the biochemical mechanisms of these important enzymes in ubiquitin biology.
Collapse
|