Explore the vast range of titles available.

Current methods used for measuring amino acid side-chain reactivity lack the throughput needed to screen large chemical libraries for interactions across the proteome. Here we redesigned the workflow for activity-based protein profiling of reactive cysteine residues by using a smaller desthiobiotin-based probe, sample multiplexing, reduced protein starting amounts and software to boost data acquisition in real time on the mass spectrometer. Our method, streamlined cysteine activity-based protein profiling (SLC-ABPP), achieved a 42-fold improvement in sample throughput, corresponding to profiling library members at a depth of >8,000 reactive cysteine sites at 18 min per compound. We applied it to identify proteome-wide targets of covalent inhibitors to mutant Kirsten rat sarcoma (KRAS) G12C and Bruton’s tyrosine kinase (BTK). In addition, we created a resource of cysteine reactivity to 285 electrophiles in three human cell lines, which includes >20,000 cysteines from >6,000 proteins per line. The goal of proteome-wide profiling of cysteine reactivity across thousand-member libraries under several cellular contexts is now within reach. An improved workflow enables a 42-fold higher throughput of activity-based protein profiling.

A competitive activity–based protein profiling method is reported for quantifying the reactivity of lipid-derived electrophilic compounds with cysteine residues in the human proteome. Cells produce electrophilic products with the potential to modify and affect the function of proteins. Chemoproteomic methods have provided a means to qualitatively inventory proteins targeted by endogenous electrophiles; however, ascertaining the potency and specificity of these reactions to identify the sites in the proteome that are most sensitive to electrophilic modification requires more quantitative methods. Here we describe a competitive activity–based profiling method for quantifying the reactivity of electrophilic compounds against >1,000 cysteines in parallel in the human proteome. Using this approach, we identified a select set of proteins that constitute 'hot spots' for modification by various lipid-derived electrophiles, including the oxidative stress product 4-hydroxy-2-nonenal (HNE). We show that one of these proteins, ZAK kinase, is labeled by HNE on a conserved, active site–proximal cysteine and that the resulting enzyme inhibition creates a negative feedback mechanism that can suppress the activation of JNK pathways normally induced by oxidative stress.

Nucleophilic amino acids make important contributions to protein function, including performing key roles in catalysis and serving as sites for post-translational modification. Electrophilic groups that target amino-acid nucleophiles have been used to create covalent ligands and drugs, but have, so far, been mainly limited to cysteine and serine. Here, we report a chemical proteomic platform for the global and quantitative analysis of lysine residues in native biological systems. We have quantified, in total, more than 9,000 lysines in human cell proteomes and have identified several hundred residues with heightened reactivity that are enriched at protein functional sites and can frequently be targeted by electrophilic small molecules. We have also discovered lysine-reactive fragment electrophiles that inhibit enzymes by active site and allosteric mechanisms, as well as disrupt protein–protein interactions in transcriptional regulatory complexes, emphasizing the broad potential and diverse functional consequences of liganding lysine residues throughout the human proteome. A chemical proteomic strategy has now been reported for the global profiling of lysine reactivity and ligandability. Using this approach, >9000 lysines in the human proteome were evaluated, leading to the discovery of hyper-reactive lysines, and lysines that can be targeted by electrophilic small molecules to perturb enzyme function and protein–protein interactions.

The posttranslational modification of proteins and their regulation by metabolites represent conserved mechanisms in biology. At the confluence of these two processes, we report that the primary glycolytic intermediate 1,3-bisphosphoglycerate (1,3-BPG) reacts with select lysine residues in proteins to form 3-phosphoglyceryl-lysine (pgK). This reaction, which does not require enzyme catalysis, but rather exploits the electrophilicity of 1,3-BPG, was found by proteomic profiling to be enriched on diverse classes of proteins and prominently in or around the active sites of glycolytic enzymes. pgK modifications inhibit glycolytic enzymes and, in cells exposed to high glucose, accumulate on these enzymes to create a potential feedback mechanism that contributes to the buildup and redirection of glycolytic intermediates to alternate biosynthetic pathways.

S-palmitoylation is a protein post-translational modification involved in trafficking, compartmentalization and membrane-tethering of various proteins. A palmitic acid analog, 17-octadecynoic acid, serves as a metabolically incorporated bioorthogonal click chemistry probe for detecting S-palmitoylated human proteins by mass spectrometry or in-gel fluorescence. S-palmitoylation is a pervasive post-translational modification required for the trafficking, compartmentalization and membrane tethering of many proteins. We demonstrate that the commercially available compound 17-octadecynoic acid (17-ODYA) can serve as a bioorthogonal, click chemistry probe for in situ labeling, identification and verification of palmitoylated proteins in human cells. We identified ∼125 predicted palmitoylated proteins, including G proteins, receptors and a family of uncharacterized hydrolases whose plasma membrane localization depends on palmitoylation.

Recent advances in chemical proteomics have begun to characterize the reactivity and ligandability of lysines on a global scale. Yet, only a limited diversity of aminophilic electrophiles have been evaluated for interactions with the lysine proteome. Here, we report an in-depth profiling of >30 uncharted aminophilic chemotypes that greatly expands the content of ligandable lysines in human proteins. Aminophilic electrophiles showed disparate proteomic reactivities that range from selective interactions with a handful of lysines to, for a set of dicarboxaldehyde fragments, remarkably broad engagement of the covalent small-molecule–lysine interactions captured by the entire library. We used these latter ‘scout’ electrophiles to efficiently map ligandable lysines in primary human immune cells under stimulatory conditions. Finally, we show that aminophilic compounds perturb diverse biochemical functions through site-selective modification of lysines in proteins, including protein–RNA interactions implicated in innate immune responses. These findings support the broad potential of covalent chemistry for targeting functional lysines in the human proteome.A deep chemical proteomic investigation of diverse aminophilic electrophiles has identified ligandable lysines across a wide range of human proteins. The proteins cover different functional and structural classes, and the aminophilic electrophiles include compounds that disrupt protein–protein and protein–RNA interactions. This dataset provides a proteome-wide atlas of lysine-reactive chemistry.

Proteomics has revealed that the ~20,000 human genes engender a far greater number of proteins, or proteoforms, that are diversified in large part by post-translational modifications (PTMs). How such PTMs affect protein structure and function is an active area of research but remains technically challenging to assess on a proteome-wide scale. Here, we describe a chemical proteomic method to quantitatively relate serine/threonine phosphorylation to changes in the reactivity of cysteine residues, a parameter that can affect the potential for cysteines to be post-translationally modified or engaged by covalent drugs. Leveraging the extensive high-stoichiometry phosphorylation occurring in mitotic cells, we discover numerous cysteines that exhibit phosphorylation-dependent changes in reactivity on diverse proteins enriched in cell cycle regulatory pathways. The discovery of bidirectional changes in cysteine reactivity often occurring in proximity to serine/threonine phosphorylation events points to the broad impact of phosphorylation on the chemical reactivity of proteins and the future potential to create small-molecule probes that differentially target proteoforms with PTMs. This article describes a chemical proteomic approach to quantitatively relate serine/threonine phosphorylation to changes in the reactivity of cysteine residues, thereby affecting their potential to be post-translationally modified and/or targeted by electrophilic small molecules.

Key Points Activity-based protein profiling (ABPP) facilitates the discovery of deregulated enzymes in cancer. Competitive ABPP yields selective inhibitors for functional characterization of cancer enzymes. ABPP can be integrated with metabolomics to map deregulated enzymatic pathways in cancer. ABPP can be integrated with other proteomic methods to map proteolytic pathways in cancer. ABPP probes can be used to image tumour development in living animals. This Review focuses on activity-based protein profiling, which enables the discovery of cancer-relevant enzymes and selective pharmacological probes to perturb and characterize these proteins in tumour cells. When ABPP is integrated with other large-scale profiling methods, it can provide insight into the metabolic and signalling pathways that support cancer pathogenesis and indicate new strategies for treatment. Large-scale profiling methods have uncovered numerous gene and protein expression changes that correlate with tumorigenesis. However, determining the relevance of these expression changes and which biochemical pathways they affect has been hindered by our incomplete understanding of the proteome and its myriad functions and modes of regulation. Activity-based profiling platforms enable both the discovery of cancer-relevant enzymes and selective pharmacological probes to perturb and characterize these proteins in tumour cells. When integrated with other large-scale profiling methods, activity-based proteomics can provide insight into the metabolic and signalling pathways that support cancer pathogenesis and illuminate new strategies for disease diagnosis and treatment.

A quantitative proteomics approach to characterize protein palmitoylation dynamics on a global scale in cells, as well as to identify enzymes responsible for the regulation of palmitoylation, is described. The reversible thioester linkage of palmitic acid on cysteines, known as protein S-palmitoylation, facilitates the membrane association and proper subcellular localization of proteins. Here we report the metabolic incorporation of the palmitic acid analog 17-octadecynoic acid (17-ODYA) in combination with stable-isotope labeling with amino acids in cell culture (SILAC) and pulse-chase methods to generate a global quantitative map of dynamic protein palmitoylation events in cells. We distinguished stably palmitoylated proteins from those that turn over rapidly. Treatment with a serine lipase–selective inhibitor identified a pool of dynamically palmitoylated proteins regulated by palmitoyl-protein thioesterases. This subset was enriched in oncoproteins and other proteins linked to aberrant cell growth, migration and cancer. Our method provides a straightforward way to characterize global palmitoylation dynamics in cells and confirms enzyme-mediated depalmitoylation as a critical regulatory mechanism for a specific subset of rapidly cycling palmitoylated proteins.

A decline in stem cell function impairs tissue regeneration during ageing, but the role of the stem-cell-supporting niche in ageing is not well understood. The small intestine is maintained by actively cycling intestinal stem cells that are regulated by the Paneth cell niche 1 , 2 . Here we show that the regenerative potential of human and mouse intestinal epithelium diminishes with age owing to defects in both stem cells and their niche. The functional decline was caused by a decrease in stemness-maintaining Wnt signalling due to production of Notum, an extracellular Wnt inhibitor, in aged Paneth cells. Mechanistically, high activity of mammalian target of rapamycin complex 1 (mTORC1) in aged Paneth cells inhibits activity of peroxisome proliferator activated receptor α (PPAR-α) 3 , and lowered PPAR-α activity increased Notum expression. Genetic targeting of Notum or Wnt supplementation restored function of aged intestinal organoids. Moreover, pharmacological inhibition of Notum in mice enhanced the regenerative capacity of aged stem cells and promoted recovery from chemotherapy-induced damage. Our results reveal a role of the stem cell niche in ageing and demonstrate that targeting of Notum can promote regeneration of aged tissues. Ageing-associated decline in intestinal stem cell function is mediated by increased Notum, a protein inhibitor of stemness-maintaining Wnt signalling, which is secreted by Paneth cells.