K48- and K63-linked ubiquitin chain interactome reveals branch- and length-specific ubiquitin interactors
Ontology highlight
ABSTRACT:
INSTRUMENT(S): Orbitrap Exploris 480
ORGANISM(S): Candida Albicans
SUBMITTER: 
Oliver Popp
LAB HEAD: Thomas Sommer
PROVIDER: PXD051890 | Pride | 2024-05-15
REPOSITORIES: Pride
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Project description:SpyTagged branched and unbranched K48- and K63-linked Tetra-Ubiquitin chains were immobilized on SpyCatcher agarose (48Ub4; 63Ub4; [Ub]2-48,63Ub-48Ub; [Ub]2-48,63Ub-63Ub). Pulldown were performed from protease-inhibitor treated U2OS cell lines to identify specific binders of K48-K63-branched Ub4.
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Project description:Assembly of polymeric ubiquitin (Ub) chains is an essential posttranslational protein modification that regulates widespread intracellular processes in eukaryotic cells. Factors and mechanisms that regulate the formation of Ub chains are key to the understanding of many cellular processes. The E2 enzyme Ubc1 (Ube2K) exclusively targets K48 in Ub for chain formation and has been linked to cell-cycle progression and proteostasis. Uniquely among E2 enzymes, it harbors a Ub binding UBA domain, which has been implicated in Ub chain formation but its function remained elusive. Through in vitro binding experiments, we unexpectedly found that the UBA domain enables preferential binding of K63-linked Ub chains. Based on structural modeling, extensive in vitro ubiquitination experiments and NMR binding studies, we propose a mechanism through which Ubc1 selectively forms K48/K63 branched Ub chains – an usual chain architecture, about whose prevalence and function little is known to date. Ultimately, we link UBA dependent activity of Ubc1 to its role in proteostasis through genetic experiments.
2021-09-09 | PXD018651 | Pride
Project description:Post-translational control by ubiquitin regulates various aspects of cellular biology. This chemical modification on proteins presents itself in numerous iterations, from a single mono-ubiquitination event to chains of poly-ubiquitin. Among the various types of poly-ubiquitin constructed are untethered species that comprise a series of ubiquitin moieties linked to one another, but free from another protein. The current notion is that these unanchored poly-ubiquitin species are deleterious to the cell and are rapidly deconstructed. We recently examined the toxicity and utilization of untethered poly-ubiquitin in an intact organism by using the fruit fly, Drosophila melanogaster. We found that these ubiquitin species are largely innocuous to flies and that free poly-Ub can be controlled by being degraded by the proteasome or being conjugated onto another protein as a single unit. However, whether the fly is mounting an organismal defense against untethered chains was not explored in detail. Here, we conducted RNA-seq analyses to examine at the transcriptome level the impact of unanchored poly-Ub in the fly. We found ~90 transcripts whose expression is altered in the presence of different types of unanchored poly-ubiquitin. The set of genes identified was mostly devoid of ubiquitin-, proteasome- or autophagy-related components. The largest gene ontology category identified, housing ~15 of the altered genes, was proteolysis. The seeming absence of a large and multipronged response to unanchored ubiquitin chains in the fly supports the conclusion that these species need not be toxic in vivo and underscores the need to reexamine the role of free ubiquitin chains in the cell. We designed two types of poly-Ub chains with six Ub molecules in tandem. They cannot be cleaved by DUBs (there are no "GG" motifs linking the Ub molecules). Ub6-GG can be conjugated in toto onto other proteins; Ub6-Stop cannot. We drove ubiquitous expression using sqh-Gal4, and then performed RNA-Seq on adult flies to determine any cellular response to the presence of our unanchored Ub chains.
2019-05-01 | GSE125090 | GEO
Project description:The attachment of differently linked ubiquitin (Ub) chains of varying length to proteins is a prevalent posttranslational modification in eukaryotic cells. The fate of a modified protein is determined by Ub-binding proteins (UBPs) that interact with Ub chains in a linkage-selective manner. Therefore, proteome-wide interaction studies using differently linked Ub chains have become a focus of research activities. However, the impact and functional consequences of chain length on the binding selectivity of UBPs remain mostly elusive, due to a lack of available tools and sufficient amounts of pure, length-defined Ub chains. Here we generated linkage- and length-defined Ub chains using click-chemistry and gel-free fractionation and employed such defined polymers in affinity-based enrichment assays to identify length- and linkage-selective interactors on a proteome-wide scale. For the first time, this revealed that the length of a Ub chain has generally a major impact on its ability to be selectively recognized by UBPs.
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Project description:The assembly of a specific polymeric ubiquitin (Ub) chain on a target protein is a key event in the regulation of numerous cellular processes. Yet, the mechanisms that govern the selective synthesis of particular polyubiquitin signals remain enigmatic. The ubiquitin-conjugating (E2) enzymes Ubc1 in yeast and Ube2K in mammals exclusively generate polyubiquitin linked through lysine 48 (K48). Uniquely among E2 enzymes, Ubc1 and Ube2K harbor a Ub binding UBA domain with unknown function. We found that this UBA domain preferentially interacts with Ub chains linked through lysine 63 (K63). Based on structural modeling, in vitro ubiquitination experiments and NMR studies, we propose that the UBA domain aligns Ubc1 with K63-linked polyubiquitin and facilitates the selective assembly of K48/K63-branched Ub molecules. Genetic experiments link the activity of the UBA domain and hence the formation of this unusual Ub chain topology to the maintenance of cellular proteostasis.
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2023-09-28 | PXD045936 |
Project description:The OTU deubiquitinase TRABID is highly tuned for the recognition and cleavage of K29 and K33-linked ubiquitin chains. Yet the cellular functions of these atypical ubiquitin signals remain unclear. Here, we compared the interactome of two different catalytically-dead TRABID constructs, one that lacks the OTU domain and the other a single point mutant that is catalytically inactive. Since both constructs also act as ubiquitin trapping mutants, this approach was used to differentiate between interactors and substrates. The E3 ubiquitin ligase HECTD1 was confirmed as a TRABID substrate, and using UbiCREST and Ubiquitin-AQUA proteomics, we determined that HECTD1 preferentially assembles K29- and K48-linked ubiquitin chains. Further in vitro autoubiquitination assays using ubiquitin mutants established that in contrast to UBE3C, HECTD1 requires the formation of branched K29/K48-linked chains for its full activity. Finally, we used transient knockdown and genetic knock out of TRABID in mammalian cells to show that TRABID stabilises HECTD1 protein levels. This study identifies TRABID-HECTD1 as a K29-specific DUB/E3 pair and provides novel insights on the assembly of branched ubiquitin signals.
2021-06-23 | PXD022703 | Pride
Project description:Ubiquitin is a highly conserved eukaryotic protein responsible for regulating a variety of functions when conjugated to target proteins. Ubiquitin is essential, accumulates during the stress response, and is the canonical signal for protein degradation by the proteasome. Still, the function of ubiquitin in response to oxidative stress, particularly in the removal of oxidized proteins remains elusive because of the number of potential targets and different roles that polyubiquitin chains can play. Since polyubiquitin chains linked by K48 ubiquitin are the most abundant and canonical signal for protein degradation, we investigated the roles of K48 ubiquitin in the degradation of oxidized proteins. Combining protein oxidation, linkage-specific ubiquitination screens, and quantitative proteomics, we found K48 ubiquitin accumulated in a bimodal fashion, at both the early and late phase of response. We further showed that a fraction of oxidized proteins are conjugated with K48 ubiquitin in vivo. Using quantitative proteomics we identified ~750 ubiquitinated proteins and ~400 oxidized proteins that were differentially modified during the stress response, and around half the proteins were both oxidized and ubiquitinated. These proteins were highly abundant and function in translation and energy metabolism. Finally, we showed that the ubiquitination system is required for degradation of oxidized proteins, suggesting that oxidized proteins that rapidly accumulate during stress are ubiquitinated, and degraded during the later recovery phase. This temporal disconnect may be necessary for reprogramming protein dynamics, restoring proteostasis, and resuming cell growth.
2021-04-30 | PXD014173 | Pride
Project description:In this experiments, we used several ubiquitin activity-based probes (Ub-Prg, Ub-VME, and Ub-VS) to covalently capture ubiquitin-interacting proteins in Legionella pneumophila. These enriched interactome were analyzed by LC-MS/MS to identify Legionella effectors uniquely captured by the probes.
2023-12-09 | MSV000093623 | MassIVE
Project description:Proctor2007 - Age related decline of proteolysis, ubiquitin-proteome system
This
is a stochastic model of the ubiquitin-proteasome system for a
generic pool of native proteins (NatP), which have a half-life of
about 10 hours under normal conditions. It is assumed that these
proteins are only degraded after they have lost their native
structure due to a damage event. This is represented in the model
by the misfolding reaction which depends on the level of reactive
oxygen species (ROS) in the cell. Misfolded proteins (MisP) are
first bound by an E3 ubiquitin ligase. Ubiquitin (Ub) is
activated by E1 (ubiquitin-activating enzyme) and then passed to
E2 (ubiquitin-conjugating enzyme). The E2 enzyme then passes the
ubiquitin molecule to the E3/MisP complex with the net effect
that the misfolded protein is monoubiquitinated and both E2 and
E3 are released. Further ubiquitin molecules are added in a
step-wise manner. When the chain of ubiquitin molecules is of
length 4 or more, the polyubiquitinated misfolded protein may
bind to the proteasome. The model also includes de-ubiquitinating
enzymes (DUB) which cleave ubiquitin molecules from the chain in
a step-wise manner. They work on chains attached to misfolded
proteins both unbound and bound to the proteasomes. Misfolded
proteins bound to the proteasome may be degraded releasing
ubiquitin. Misfolded proteins including ubiquitinated proteins
may also aggregate. Aggregates (AggP) may be sequestered
(Seq_AggP) which takes them out of harm's way or they may bind to
the proteasome (AggP_Proteasome). Proteasomes bound by aggregates
are no longer available for protein degradation.
Figure
2 and Figure 3 has been simulated using Gillespie2.
This model is described in the article:
An in silico model of the
ubiquitin-proteasome system that incorporates normal
homeostasis and age-related decline.
Proctor CJ, Tsirigotis M, Gray
DA.
BMC Syst Biol 2007; 1: 17
Abstract:
BACKGROUND: The ubiquitin-proteasome system is responsible
for homeostatic degradation of intact protein substrates as
well as the elimination of damaged or misfolded proteins that
might otherwise aggregate. During ageing there is a decline in
proteasome activity and an increase in aggregated proteins.
Many neurodegenerative diseases are characterised by the
presence of distinctive ubiquitin-positive inclusion bodies in
affected regions of the brain. These inclusions consist of
insoluble, unfolded, ubiquitinated polypeptides that fail to be
targeted and degraded by the proteasome. We are using a systems
biology approach to try and determine the primary event in the
decline in proteolytic capacity with age and whether there is
in fact a vicious cycle of inhibition, with accumulating
aggregates further inhibiting proteolysis, prompting
accumulation of aggregates and so on. A stochastic model of the
ubiquitin-proteasome system has been developed using the
Systems Biology Mark-up Language (SBML). Simulations are
carried out on the BASIS (Biology of Ageing e-Science
Integration and Simulation) system and the model output is
compared to experimental data wherein levels of ubiquitin and
ubiquitinated substrates are monitored in cultured cells under
various conditions. The model can be used to predict the
effects of different experimental procedures such as inhibition
of the proteasome or shutting down the enzyme cascade
responsible for ubiquitin conjugation. RESULTS: The model
output shows good agreement with experimental data under a
number of different conditions. However, our model predicts
that monomeric ubiquitin pools are always depleted under
conditions of proteasome inhibition, whereas experimental data
show that monomeric pools were depleted in IMR-90 cells but not
in ts20 cells, suggesting that cell lines vary in their ability
to replenish ubiquitin pools and there is the need to
incorporate ubiquitin turnover into the model. Sensitivity
analysis of the model revealed which parameters have an
important effect on protein turnover and aggregation kinetics.
CONCLUSION: We have developed a model of the
ubiquitin-proteasome system using an iterative approach of
model building and validation against experimental data. Using
SBML to encode the model ensures that it can be easily modified
and extended as more data become available. Important aspects
to be included in subsequent models are details of ubiquitin
turnover, models of autophagy, the inclusion of a pool of
short-lived proteins and further details of the aggregation
process.
This model is hosted on
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BIOMD0000000105.
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2024-09-02 | BIOMD0000000105 | BioModels