Integrative Structural Characterization of the Human Canonical and Non-canonical Cop9 Signalosome Complexes
ABSTRACT: The COP9 signalosome (CSN) is an evolutionarily conserved protein complex that functions as a deneddylase to inactivate Cullin-RING E3 ligases for controlling protein ubiquitination. CSN possesses structural flexibility that is important for its activation upon binding to a diverse array of CRLs. The canonical and non-canonical CSN complexes consist of 8 (CSN1-8) and 9 (CSN1-9) subunits, respectively. Although CSN9 is not essential for CSN assembly and function, it appears to be important in non-catalytic regulation of CRLs by CSN. Here we employed a combinatory cross-linking mass spectrometry (XL-MS) approach to generate the largest PPI maps of human CSN complexes, which significantly enhanced the precision of integrative structural modeling. The resulting integrative structures allowed us not only to elucidate architectures of both complexes, but also to assess CSN structural dynamics that was not described in the crystal structure. In addition, we have determined CSN9 docking sites and its impact on the CSN structure. While CSN9 binding did not induce global conformational changes, it triggered subunit local reorientations that may be associated with CSN9 involvement in CSN-mediated steric regulation of CRLs.
Project description:Cross-linking mass spectrometry (XLMS) is becoming increasingly popular, and current advances are widening the applicability of the technique so that it can be utilized by non-specialist laboratories. Specifically, the use of novel mass spectrometry-cleavable (MS-cleavable) reagents dramatically reduces complexity of the data by providing i) characteristic reporter ions and ii) the mass of the individual peptides, rather than that of the cross-linked moiety. However, optimum acquisition strategies to obtain the best quality data for such cross-linkers with higher energy C-trap dissociation (HCD) alone is yet to be achieved. Therefore, we have carefully investigated and optimized MS parameters to facilitate the identification of disuccinimidyl sulfoxide (DSSO)-based cross-links on HCD-equipped mass spectrometers. From the comparison of 9 different fragmentation energies we chose several stepped- HCD fragmentation methods that were evaluated on a variety of cross-linked proteins. The optimal stepped-HCD method was then directly compared with previously described methods using an Orbitrap Fusion™ Lumos™ Tribrid™ instrument using a high-complexity sample. The final results indicate that our stepped-HCD method is able to identify more cross-links than other methods, mitigating the need for multistage MS (MSn) enabled instrumentation and alternative dissociation techniques.
Project description:Cross-linking mass spectrometry is an increasingly used, powerful technique to study protein-protein interactions or to provide structural information. Due to sub-stochiometric reaction efficiencies, cross-linked peptides are usually low abundant. This results in challenging data evaluation and the need for an effective enrichment. Here we describe an improved, easy to implement, one-step method to enrich azide-tagged, acid-cleavable disuccinimidyl bis-sulfoxide (DSBSO) cross-linked peptides using dibenzocyclooctyne (DBCO) coupled Sepharose������ beads. We probed this method using recombinant Cas9 and E. coli ribosome. For Cas9, the number of detectable cross-links was increased from ~100 before enrichment to 580 cross-links after enrichment. To mimic a cellular lysate, E. coli ribosome was spiked into a tryptic HEK background at a ratio of 1:2 ��������� 1:100. The number of detectable unique cross-links maintained high at ~100. The estimated enrichment efficiency was improved by factor 4 -5 (based on XL numbers) compared to enrichment via biotin and streptavidin. We were still able to detect cross-links from 0.25 ������g cross-linked E. coli ribosome in a background of 100 ������g tryptic HEK peptides, indicating a high enrichment sensitivity. In contrast to conventional enrichment techniques, like SEC, the time needed for preparation and MS measurement is significantly reduced. This robust, fast and selective enrichment method for azide-tagged linkers will contribute to map protein-protein interactions, investigate protein architectures in more depth and help to understand complex biological processes.
Project description:The application of non-cleavable cross-linkers to complex samples in XL-MS workflows is limited by the n² problem, a quadratic expansion of the search space with increasing database size. Here, a peptide-focused approach is proposed, for which cross-linking peptide candidates are identified in a parallel experiment by using a thiol-cleavable cross-linker with equal reactivity. Samples are reduced and alkylated, thereby releasing cross-linked peptides with a variable modification on the initially cross-linked residue. Modified peptides are identified by database search and concatenated to a peptide database, which is finally used for the analysis of the sample cross-linked with a non-cleavable cross-linker. This way, the search space is dramatically reduced leading to a higher sensitivity, because there is less chance for random hits to false positive sequences. The approach was benchmarked on cross-linked purified protein complexes (20 S Proteasome, yeast PolII, and TFIIH), and in vivo cross-linked bacteria (Bacillus subtilis, Bacillus cereus) by comparing it to the conventional approach of searching against the protein sequences.
Project description:The endogenous cellular prion protein (PrPC) can misfold into the scrapie isoform (PrPSc) and cause fatal infectious diseases. Despite significant research on the prion protein, both its normal function and whether alterations to that function play a critical role in prion diseases remain unknown. The protein consists of a predominantly alpha-helical C-terminal domain and an unstructured N-terminal domain that can coordinate Cu2+. Previous studies using NMR and EPR have revealed a tertiary association between the N-terminal domain and the C-terminal domain that we have hypothesized to be critical to the protein’s normal function. Here we investigated and quantified the inter-domain interactions within three different prion variants (wild type recombinant mouse PrPC, mutant delta central region (ΔCR), and disease mutant (E199K) after chemical cross-linking with a newly designed MS-cleavable reagent 1-(4-((2,5-Dioxopyrrolidin-1-yl)oxy)-4-oxobutyl)-4-(2-(3-methyl-3H-diazirin-3-yl)ethyl)-1,4-diazabicyclo[2.2.2] octane-1,4-diium (APDC4), followed by nHPLC(RP) and tandem MS analysis.
Project description:Dynamic proteins and multi-protein complexes govern most biological processes. Cross-linking/mass spectrometry (CLMS) is increasingly successful in providing residue-resolution data on static proteinaceous structures. In order to investigate the technical feasibility of recording dynamic processes using isotope-labelling for quantitation, we generated a model dataset by cross-linking human serum albumin (HSA) with the readily available cross-linker BS3-d0/d4 in different heavy/light ratios.
Project description:Cleavage factor II (CF II) is a poorly characterized component of the multi-protein complex catalyzing 3' cleavage and polyadenylation of mammalian mRNA precursors. We have reconstituted CF II as a heterodimer of hPcf11 and hClp1. The heterodimer is active in partially reconstituted cleavage reactions, whereas hClp1 by itself is not. Pcf11 moderately stimulates the RNA 5' kinase activity of hClp1; the kinase activity is dispensable for RNA cleavage. CF II binds RNA with nanomolar affinity. Binding is mediated mostly by the two zinc fingers in the C-terminal region of hPcf11. RNA is bound without pronounced sequence-specificity, but extended G-rich sequences appear to be preferred. We discuss the possibility that CF II contributes to the recognition of cleavage/polyadenylation substrates through interaction with G-rich far-downstream sequence elements.
Project description:Dynamic proteins and multi-protein complexes govern most biological processes. Cross-linking/mass spectrometry (CLMS) is increasingly successful in providing residue- resolution data on static proteinaceous structures. Here we investigate the technical feasibility of recording dynamic processes using isotope-labelling for quantitation. We cross-linked human serum albumin (HSA) with the readily available cross-linker BS3-d0/4 in different heavy/light ratios. Wefound two limitations. First, isotope labelling reduced the number of identified cross-links. This is in line with similar findings when identifying proteins. Second, standard quantitative proteomics software was not suitable for work with cross-linking. To ameliorate this we wrote a basic open source application, XiQ. Using XiQ we could establish that quantitative CLMS was technically feasible. Biological significance Cross-linking/mass spectrometry (CLMS) has become a powerful tool for providing residue- resolution data on static proteinaceous structures. Adding quantitation to CLMS will extend its ability of recording dynamic processes. Here we introduce a cross-linking specific quantitation strategy by using isotope labelled cross-linkers. Using a model system, we demonstrate the principle and feasibility of quantifying cross-linking data and discuss challenges one may encounter while doing so.We then provide a basic open source application, XiQ, to carry out automated quantitation of CLMS data. Ourwork lays the foundations of studying themolecular details of biological processes at greater ease than this could be done so far.
Project description:Protein-protein interactions within complexes and networks are often dynamic and their elucidation remains a challenging task. Here, we show on the example of the proteolytic ClpXP complex the power of combined chemical cross-linking and mass-spectrometry to capture transient binding interactions within ClpP and ClpX as well as across the enigmatic ClpX hexamer – ClpP heptamer interface. Our data suggests that a few hot spot lysine residues located in signature loops in ClpX mediate the ClpX-ClpP interaction. This study further confirms that Listeria monocytogenes ClpX solely interacts with the heterooligomeric ClpP1/2 complex via the ClpP2 apical site. Moreover, the cellular interaction network of human and bacterial proteases was elucidated via in situ chemical cross-linking followed by an antibody-based pull-down against ClpP from genetically unmodified cells. A subsequent gel-free, quantitative mass spectrometric analysis demonstrated an up to 3-fold higher coverage compared to conventional co-immunoprecipitation without cross-linker revealing unprecedented insight into intracellular ClpXP networks.