Combinatorial mapping of E3 ubiquitin ligases to their target substrates
Ontology highlight
ABSTRACT: E3 ubiquitin ligases (E3s) confer specificity of protein degradation through the recognition of specific target substrates for ubiquitination and subsequent degradation, making E3s attractive candidates for drug development. There are over 600 annotated E3s in the human genome, yet the vast majority have no known substrate proteins, due in part to the limited scalability of methods to evaluate the vast number of potential E3-substrate interactions. To address this, we developed COMET (Combinatorial Mapping of E3 Targets), a combinatorial framework that can test the role of many specific E3s in regulating the abundance of many specific substrates, within the context of a single experiment. As a proof-of-concept, we applied COMET to identify specific E3 subunits of the SCF ubiquitin ligase complex that mediate the degradation of target substrates, including short-lived transcription factors (TFs). Our data suggest that many E3-substrate relationships are complex rather than simple 1:1 associations. Further, we provide computational models of E3-substrate interactions from our screen. Looking forward, we anticipate that COMET can be further scaled to enable comprehensive mapping of regulators of protein stability to their target substrates
Project description:The E3 ubiquitin -protein ligases (E3s) plays a role as regulators of protein trafficking and degradation. We aimed to identify E3s in rat kidney which are associated with dDAVP-induced urine concentration.
Project description:The E3 ubiquitin -protein ligases (E3s) plays a role as regulators of protein trafficking and degradation. We aimed to identify E3s in rat kidney which are associated with dDAVP-induced urine concentration. Kidney inner medulla collected from vehicle treated control (n=2), dDAVP infusion for 5 d (D5d, n=2) and 3 h-withdrawal of dDAVP after 5 d-infusion (D5d-3h, n=2) groups were subjected to a transcriptome analysis.
Project description:The protein ubiquitylation is under the equilibrium between ubiquitin conjugation and deconjugation. How substrates stabilized by deubiquitylation are directed for degradation remains unclear. Branched ubiquitin chains promote substrate degradation through the proteasome, but the underlying mechanisms are not fully understood. TRIP12 and UBR5 are HECT-type E3s specific for the K29 and K48 linkages, respectively. Here, we show that the deubiquitylase (DUB) OTUD5 is cooperatively modified by TRIP12 and UBR5, resulting in the conjugation of K29/K48 branched ubiquitin chains and accelerated proteasomal degradation. The TRIP12–OTUD5 antagonism regulates TNF-–induced NF-B signaling. Mechanistically, although OTUD5 readily cleaves K48 linkages, K29 linkages are resistant against OTUD5 activity. Consequently, K29 linkages overcome OTUD5 DUB activity to facilitate UBR5-dependent K48-linked chain branching. This mechanism is applicable to other TRIP12 substrates associated with OTUD5. These results reveal a unique cellular strategy in which the combination of DUB-resistant and proteasome-targeting ubiquitin linkages efficiently promotes the degradation of substrates protected by deubiquitylation, underscoring the role of branched ubiquitin chains in shifting the ubiquitin conjugation/deconjugation equilibrium.
Project description:Ubiquitin and ubiquitin-like conjugation cascades consist of dedicated E1, E2 and E3 enzymes with E3s providing substrate specificity. Mass spectrometry-based approaches have enabled the identification of more than 60,000 acceptor sites for ubiquitin and 40,000 acceptor sites for SUMO2/3. However, E3-to-target wiring is poorly understood. The limited number of SUMO E3s provides the unique opportunity to systematically study E3-substrate wiring. We developed SUMO Activated Target Traps (SATTs) and, in the presence of proteasome inhibitor MG132,systematically identified substrates for eight different SUMO E3s, PIAS1, PIAS2, PIAS3, PIAS4, NSMCE2, ZNF451, LAZSUL(ZNF451-3) and ZMIZ2. SATTs enabled us to identify 427 SUMO1 and 961 SUMO2/3 targets in an E3-specific manner. We found pronounced E3 substrate preference, even at the substrate isoform level. Quantitative proteomics enabled us to measure substrate specificity of E3s, quantified using the SATT index. Furthermore, we developed the Polar SATTs web-based tool (https://amsterdamstudygroup.shinyapps.io/polarVolcaNoseR_revised/) to browse the dataset in an interactive manner, increasing the accessibility of this resource for the community. Overall, we uncover E3-to-target wiring of 1388 SUMO substrates, highlighting unique and overlapping sets of substrates for eight different SUMO E3 ligases.
Project description:We describe a new class of reagents for identifying substrates, adaptors, and regulators of HECT and RING E3s. UBAITs (Ubiquitin-Activated Interaction Traps) are E3-ubiquitin fusion proteins, and in an E1- and E2-dependent manner, the C-terminal ubiquitin moiety forms an amide linkage to proteins that interact with the E3, enabling covalent co-purification of the E3 with partner proteins. UBAITs were made for both HECT (Rsp5, Itch) and RING (Psh1, RNF126, RNF168) E3s. For HECT E3s, substrate trapping occurred in vitro either through an E3 thioester-linked lariat intermediate or an E2 thioester intermediate, and both WT and active site mutant UBAITs trapped known interacting proteins in yeast and human cells. Yeast Psh1 and human RNF126 and RNF168 UBAITs also trapped known interacting proteins when expressed in cells.
Project description:Reversibility of protein ubiquitylation play essential roles in cellular protein homeostasis. How substrates stabilized by deubiquitylation are directed for degradation remains largely elusive. Here, we show that the branched ubiquitin chains promote the degradation of the deubiquitylase (DUB) OTUD5. OTUD5 is sequentially modified by TRIP12 and UBR5, E3s specific for the K29 and K48 linkages, respectively, resulting in the conjugation of K29/K48 branched ubiquitin chains. The TRIP12-OTUD5 antagonism regulates TNF--induced NF-B signaling. Mechanistically, while OTUD5 readily cleaves K48-linkages, K29-linkages are resistant against OTUD5 activity. Consequently, K29-linkages overcome OTUD5 DUB activity to facilitate UBR5-dependent K48-linked chain branching. Regarding generality, this mechanism adopts to other TRIP12 substrates associated with OTUD5. These results uncover a cellular unique strategy in which the sequential addition of DUB-resistant and proteasome-targeting ubiquitin linkages efficiently promote degradation of substrates protected by deubiquitylation, underscoring the role of branched ubiquitin chains in the quality control of hard-to-degrade substrates.
Project description:VCP is an evolutionary conserved ubiquitin-dependent ATPase that mediates the degradation of proteins through the ubiquitin-proteasome pathway. Despite the central role of VCP in the regulation of protein homeostasis, identity and nature of its cellular substrates remain poorly defined. Here, we combined chemical inhibition of VCP and quantitative ubiquitin remnant profiling to assess the effect of VCP inhibition on the ubiquitin-modified proteome and to probe the substrate spectrum of VCP in human cells. We demonstrate that inhibition of VCP perturbs cellular ubiquitylation and increases ubiquitylation of a different subset of proteins compared to proteasome inhibition. VCP inhibition globally upregulates K6-linked ubiquitylation that is dependent on the HECT-type ubiquitin E3 ligase HUWE1. We report ~450 putative VCP substrates, many of which function in nuclear processes, including gene expression, DNA repair and cell cycle. Moreover, we identify that VCP regulates the level and activity of the transcription factor c-Myc.
Project description:How are E3 ubiquitin ligases configured to match substrate quaternary structures? Here, by studying the yeast GID complex, mutation of which is Glucose-Induced Degradation deficient, we discover supramolecular chelate assembly as an E3 ligase strategy for targeting an oligomeric substrate. Cryo EM structures show that to bind the tetrameric substrate fructose-1,6-bisphosphatase (Fbp1), two otherwise functional GID E3s assemble into a 20-protein Chelator-GIDSR4, which resembles an organometallic supramolecular chelate. The Chelator-GIDSR4 assembly avidly binds multiple Fbp1 degrons and positions Fbp1 so that its protomers are simultaneously ubiquitylated at lysines near its allosteric and substrate binding sites. Significantly, key structural and biochemical features - including capacity for supramolecular assembly - are preserved in the human ortholog, the CTLH E3. Based on our integrative structural, biochemical and cell biological data, we propose that higher-order E3 ligase assembly generally underlies multipronged targeting, capable of simultaneously incapacitating multiple protomers and functionalities of oligomeric substrates.
Project description:Fbw7, the substrate recognition subunit of SCF(Fbw7) ubiquitin ligase, mediates turnover of multiple proto-oncoproteins and promotes its own degradation. Fbw7-mediated substrate degradation is antagonized by the Usp28 deubiquitinase. We now show, using knockout mice, that Usp28 preferentially deubiquitinates and stabilizes Fbw7. Monoallelic deletion of Usp28 maintains stable Fbw7 but destabilizes Fbw7 substrates. In contrast, complete knockout of Usp28 promotes Pin1-dependent autocatalytic turnover of Fbw7, accumulation of Fbw7 substrates and oncogenic transformation. Overexpression of Usp28 stabilizes both Fbw7 and its substrates and similarly enhances transformation. We propose that dual regulation of Fbw7 activity by Usp28 maintains physiological levels of Fbw7 substrates, and that both loss and overexpression of Usp28 in human cancer promote Fbw7 substrate accumulation.