Large-scale identification of ubiquitination sites by mass spectrometry
TL;DR: Detailed, step-by-step instructions for sample preparation, off-line fractionation by reversed-phase chromatography at pH 10, immobilization of an antibody specific to K-ɛ-GG to beads by chemical cross-linking, enrichment of ubiquitinated peptides using these antibodies and proteomic analysis of enriched samples by LC–tandem MS (MS/MS).
Abstract: Ubiquitination is essential for the regulation of cellular protein homeostasis. It also has a central role in numerous signaling events. Recent advances in the production and availability of antibodies that recognize the Lys-ɛ-Gly-Gly (K-ɛ-GG) remnant produced by trypsin digestion of proteins having ubiquitinated lysine side chains have markedly improved the ability to enrich and detect endogenous ubiquitination sites by mass spectrometry (MS). The following protocol describes the steps required to complete a large-scale ubiquitin experiment for the detection of tens of thousands of distinct ubiquitination sites from cell lines or tissue samples. Specifically, we present detailed, step-by-step instructions for sample preparation, off-line fractionation by reversed-phase chromatography at pH 10, immobilization of an antibody specific to K-ɛ-GG to beads by chemical cross-linking, enrichment of ubiquitinated peptides using these antibodies and proteomic analysis of enriched samples by LC-tandem MS (MS/MS). Relative quantification can be achieved by performing stable isotope labeling by amino acids in cell culture (SILAC) labeling of cells. After cell or tissue samples have been prepared for lysis, the described protocol can be completed in ∼5 d.
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TL;DR: Using quantitative proteomics, it is found that lenalidomide causes selective ubiquitination and degradation of two lymphoid transcription factors, IKZF1 and IKzF3, by the CRBN-CRL4 ubiquitin ligase, which are essential transcription factors in multiple myeloma.
Abstract: Lenalidomide is a drug with clinical efficacy in multiple myeloma and other B cell neoplasms, but its mechanism of action is unknown. Using quantitative proteomics, we found that lenalidomide causes selective ubiquitination and degradation of two lymphoid transcription factors, IKZF1 and IKZF3, by the CRBN-CRL4 ubiquitin ligase. IKZF1 and IKZF3 are essential transcription factors in multiple myeloma. A single amino acid substitution of IKZF3 conferred resistance to lenalidomide-induced degradation and rescued lenalidomide-induced inhibition of cell growth. Similarly, we found that lenalidomide-induced interleukin-2 production in T cells is due to depletion of IKZF1 and IKZF3. These findings reveal a previously unknown mechanism of action for a therapeutic agent: alteration of the activity of an E3 ubiquitin ligase, leading to selective degradation of specific targets.
1,254 citations
TL;DR: It is demonstrated that lenalidomide induces the ubiquitination of casein kinase 1A1 (CK1α) by the E3 ubiquitin ligase CUL4–RBX1–DDB1–CRBN (known as CRL4CRBN), resulting in CK1α degradation.
Abstract: Lenalidomide is a highly effective treatment for myelodysplastic syndrome (MDS) with deletion of chromosome 5q (del(5q)). Here, we demonstrate that lenalidomide induces the ubiquitination of casein kinase 1A1 (CK1α) by the E3 ubiquitin ligase CUL4-RBX1-DDB1-CRBN (known as CRL4(CRBN)), resulting in CK1α degradation. CK1α is encoded by a gene within the common deleted region for del(5q) MDS and haploinsufficient expression sensitizes cells to lenalidomide therapy, providing a mechanistic basis for the therapeutic window of lenalidomide in del(5q) MDS. We found that mouse cells are resistant to lenalidomide but that changing a single amino acid in mouse Crbn to the corresponding human residue enables lenalidomide-dependent degradation of CK1α. We further demonstrate that minor side chain modifications in thalidomide and a novel analogue, CC-122, can modulate the spectrum of substrates targeted by CRL4(CRBN). These findings have implications for the clinical activity of lenalidomide and related compounds, and demonstrate the therapeutic potential of novel modulators of E3 ubiquitin ligases.
583 citations
TL;DR: a4−/− mice exhibit a profound accumulation of iron in splenic macrophages, which are critical for the reutilization of iron from engulfed red blood cells, and a previously unappreciated role for autophagy and NCOA4 in the control of iron homeostasis in vivo is revealed.
Abstract: Murphy and colleagues generate an inhibitor of the lipid kinase VPS34, which they use to uncover autophagy substrates. One of their targets, NCOA4, regulates iron homeostasis by binding ferritin heavy chain-1 and targeting ferritin to autolysosomes.
485 citations
TL;DR: A concurrent multi-omics study of SARS CoV-2 and SARS-CoV was conducted in this article, where the authors profiled the interactomes of both viruses, as well as their influence on the transcriptome, proteome, ubiquitinome and phosphoproteome of a lung derived human cell line.
Abstract: The emergence and global spread of SARS-CoV-2 has resulted in the urgent need for an in-depth understanding of molecular functions of viral proteins and their interactions with the host proteome. Several individual omics studies have extended our knowledge of COVID-19 pathophysiology1-10. Integration of such datasets to obtain a holistic view of virus-host interactions and to define the pathogenic properties of SARS-CoV-2 is limited by the heterogeneity of the experimental systems. Here we report a concurrent multi-omics study of SARS-CoV-2 and SARS-CoV. Using state-of-the-art proteomics, we profiled the interactomes of both viruses, as well as their influence on the transcriptome, proteome, ubiquitinome and phosphoproteome of a lung-derived human cell line. Projecting these data onto the global network of cellular interactions revealed crosstalk between the perturbations taking place upon infection with SARS-CoV-2 and SARS-CoV at different levels and enabled identification of distinct and common molecular mechanisms of these closely related coronaviruses. The TGF-β pathway, known for its involvement in tissue fibrosis, was specifically dysregulated by SARS-CoV-2 ORF8 and autophagy was specifically dysregulated by SARS-CoV-2 ORF3. The extensive dataset (available at https://covinet.innatelab.org ) highlights many hotspots that could be targeted by existing drugs and may be used to guide rational design of virus- and host-directed therapies, which we exemplify by identifying inhibitors of kinases and matrix metalloproteases with potent antiviral effects against SARS-CoV-2.
354 citations
TL;DR: This protocol is formulated to promote ease of use and robustness, which enable parallel digestion with each of the six tested proteases, namely chymotrypsin, LysC, LysN, AspN, GluC and ArgC.
Abstract: Protein digestion using a dedicated protease represents a key element in a typical mass spectrometry (MS)-based shotgun proteomics experiment. Up to now, digestion has been predominantly performed with trypsin, mainly because of its high specificity, widespread availability and ease of use. Lately, it has become apparent that the sole use of trypsin in bottom-up proteomics may impose certain limits in our ability to grasp the full proteome, missing out particular sites of post-translational modifications, protein segments or even subsets of proteins. To overcome this problem, the proteomics community has begun to explore alternative proteases to complement trypsin. However, protocols, as well as expected results generated from these alternative proteases, have not been systematically documented. Therefore, here we provide an optimized protocol for six alternative proteases that have already shown promise in their applicability in proteomics, namely chymotrypsin, LysC, LysN, AspN, GluC and ArgC. This protocol is formulated to promote ease of use and robustness, which enable parallel digestion with each of the six tested proteases. We present data on protease availability and usage including recommendations for reagent preparation. We additionally describe the appropriate MS data analysis methods and the anticipated results in the case of the analysis of a single protein (BSA) and a more complex cellular lysate (Escherichia coli). The digestion protocol presented here is convenient and robust and can be completed in ∼2 d.
333 citations
References
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TL;DR: MaxQuant, an integrated suite of algorithms specifically developed for high-resolution, quantitative MS data, detects peaks, isotope clusters and stable amino acid isotope–labeled (SILAC) peptide pairs as three-dimensional objects in m/z, elution time and signal intensity space and achieves mass accuracy in the p.p.b. range.
Abstract: Efficient analysis of very large amounts of raw data for peptide identification and protein quantification is a principal challenge in mass spectrometry (MS)-based proteomics. Here we describe MaxQuant, an integrated suite of algorithms specifically developed for high-resolution, quantitative MS data. Using correlation analysis and graph theory, MaxQuant detects peaks, isotope clusters and stable amino acid isotope-labeled (SILAC) peptide pairs as three-dimensional objects in m/z, elution time and signal intensity space. By integrating multiple mass measurements and correcting for linear and nonlinear mass offsets, we achieve mass accuracy in the p.p.b. range, a sixfold increase over standard techniques. We increase the proportion of identified fragmentation spectra to 73% for SILAC peptide pairs via unambiguous assignment of isotope and missed-cleavage state and individual mass precision. MaxQuant automatically quantifies several hundred thousand peptides per SILAC-proteome experiment and allows statistically robust identification and quantification of >4,000 proteins in mammalian cell lysates.
12,340 citations
TL;DR: SILAC is a simple, inexpensive, and accurate procedure that can be used as a quantitative proteomic approach in any cell culture system and is applied to the relative quantitation of changes in protein expression during the process of muscle cell differentiation.
5,653 citations
TL;DR: A novel peptide search engine using a probabilistic scoring model that can handle data with arbitrarily high fragment mass accuracy, is able to assign and score complex patterns of post-translational modifications, and accommodates extremely large databases.
Abstract: A key step in mass spectrometry (MS)-based proteomics is the identification of peptides in sequence databases by their fragmentation spectra. Here we describe Andromeda, a novel peptide search engine using a probabilistic scoring model. On proteome data, Andromeda performs as well as Mascot, a widely used commercial search engine, as judged by sensitivity and specificity analysis based on target decoy searches. Furthermore, it can handle data with arbitrarily high fragment mass accuracy, is able to assign and score complex patterns of post-translational modifications, such as highly phosphorylated peptides, and accommodates extremely large databases. The algorithms of Andromeda are provided. Andromeda can function independently or as an integrated search engine of the widely used MaxQuant computational proteomics platform and both are freely available at www.maxquant.org. The combination enables analysis of large data sets in a simple analysis workflow on a desktop computer. For searching individual spect...
4,689 citations
TL;DR: StageTips are ordinary pipette tips containing very small disks made of beads with reversed phase, cation-exchange or anion-ex exchange surfaces embedded in a Teflon mesh that allow flexible combination of disks with different surfaces to obtain multi-functional tips.
Abstract: Mass spectrometry (MS)-based proteomics measures peptides derived from proteins by proteolytic cleavage. Before performing the analysis by matrix-assisted laser desorption/ionization-tandem mass spectrometry (MALDI-MS/MS), nanoelectrospray-MS/MS (NanoES-MS/MS) or liquid chromatography-MS/MS (LC-MS/MS), the peptide mixtures need to be cleaned, concentrated and often selectively enriched or pre-fractionated, for which we employ simple, self-made and extremely economical stop-and-go-extraction tips (StageTips). StageTips are ordinary pipette tips containing very small disks made of beads with reversed phase, cation-exchange or anion-exchange surfaces embedded in a Teflon mesh. The fixed nature of the beads allows flexible combination of disks with different surfaces to obtain multi-functional tips. Disks containing different surface functionalities and loose beads such as titania and zirconia for phosphopeptide enrichment can be combined. Incorporation into an automated workflow has also been demonstrated. Desalting and concentration takes approximately 5 min while fractionation or enrichment takes approximately 30 min.
3,515 citations
TL;DR: A proteomics approach to enrich, recover, and identify ubiquitin conjugates from Saccharomyces cerevisiae lysate provides a general tool for the large-scale analysis and characterization of protein ubiquitination.
Abstract: There is a growing need for techniques that can identify and characterize protein modifications on a large or global scale. We report here a proteomics approach to enrich, recover, and identify ubiquitin conjugates from Saccharomyces cerevisiae lysate. Ubiquitin conjugates from a strain expressing 6xHis-tagged ubiquitin were isolated, proteolyzed with trypsin and analyzed by multidimensional liquid chromatography coupled with tandem mass spectrometry (LC/LC-MS/MS) for amino acid sequence determination. We identified 1,075 proteins from the sample. In addition, we detected 110 precise ubiquitination sites present in 72 ubiquitin-protein conjugates. Finally, ubiquitin itself was found to be modified at seven lysine residues providing evidence for unexpected diversity in polyubiquitin chain topology in vivo. The methodology described here provides a general tool for the large-scale analysis and characterization of protein ubiquitination.
1,626 citations