Nature Chemical Biology

Deciphering the ubiquitin code requires homogenous, site-specifically ubiquitylated proteins, yet access to such conjugates remains a major challenge. Existing approaches are often constrained by low yields, harsh reaction conditions, engineered recognition motifs or non-native linkage architectures. Here, we present UbyW (Ubiquitylation by UBE2W), a programmable platform for site-specific ubiquitylation that repurposes the E2 enzyme UBE2W to target genetically encoded isopeptidic neo-N-termini. UbyW enables efficient generation of near-native Ub-protein conjugates across diverse protein substrates, including endogenous ubiquitylation sites within folded domains, and can be implemented through a reconstituted intracellular cascade in Escherichia coli for streamlined high-yield production. The platform further enables installation of chemical functionalities adjacent to the isopeptidic linkage, including photocrosslinkers for capturing modification-dependent interactions. Using programmable probes targeting site-specific ubiquitylation of the small GTPase Ran, we identify USP15 as a cognate deubiquitylase and show that Ran K71 monoubiquitylation disrupts key Ran-cycle interactions.

Acetylation of -tubulin K40 by -tubulin acetyltransferase 1 (ATAT1) using acetyl-coenzyme A (Ac-CoA) marks stable microtubule populations, yet chemical tools to directly measure ATAT1 ligand engagement, inhibit its activity, or visualize ATAT1-mediated modification on intact microtubules remain limited. Through the development of a quantitative binding assay, we uncovered that ATAT1 can bind unnatural cofactors but fails to efficiently use them in acyl-transfer reactions. Structure-guided mutation subsequently yielded ATAT1-L163A, which successfully installed clickable handles at the native -tubulin K40 site of synthetic tubulin peptides, -tubulin, and intact microtubules. Cu(I)-catalyzed azide-alkyne cycloaddition enabled visualization of modified microtubules by in-gel fluorescence and microscopy. Moreover, we report a p11-CoA bisubstrate inhibitor that suppressed both native acetylation and engineered acylation. Together, these tools provide chemically controlled access to ATAT1 activity and a site-verified, clickable K40 modification on intact microtubules.

Molecular glue degraders (MGDs) reprogram E3 ligases to eliminate neosubstrates, yet their application has largely been confined to CRBN. Here, we identify caspase-2 as a new neosubstrate for von Hippel-Lindau (VHL), expanding the scope of VHL-based MGDs. Guided by a focused VHL ligand library design, we employed TurboID-based proximity labeling to discover stereoisomeric compounds (dCASP2-1 and dCASP2-2) that selectively recruit caspase-2 to VHL and promote its ubiquitin-proteasome system-dependent degradation. Further structure-activity relationship (SAR) studies yielded dCASP2-3 and dCASP2-4, which enhanced degradation potency (by 622-fold relative to dCASP2-1) and abolished enantioselectivity. Mechanistic mapping localized the degrader-induced interface to a two-helix region of the caspase-2 CARD domain, with residues H33, P34, and D100 essential for VHL engagement. Degron-guided computational modeling of the VHL/MGD/caspase-2 ternary complex provided structural insight into neosubstrate recognition. Together, we report the development of VHL molecular glues that selectively and potently degrade caspase-2, offering chemical probes to interrogate its functions in apoptosis and stress responses, while broadening the substrate landscape of VHL-based MGDs.

Transcription factor-based biosensors monitor metabolites and control genetic programs, but their wider use is constrained by the limited repertoire of characterized, mutually compatible sensor parts. Here we combine a curated screen of natural LysR-type transcriptional regulators (LTTRs), the largest family of bacterial transcription factors, with systematic domain swapping. Using a standardized construction platform, we convert 17 LTTRs into whole-cell reporters in Escherichia coli. Of 16 viable circuits, nine show regulatory activity, including six ligand-inducible biosensors for acetate, benzoate, -ketoglutarate, chlorohydroquinone, L-homocysteine and salicylate. Mapping interactions across 11 LTTR systems identifies seven mutually orthogonal regulator pairs, providing, to our knowledge, the first orthogonality map for this family. We next construct 108 chimeras across three domain-swap architectures; 69 retain measurable activity, with functional outcomes enriched when the native hinge-ligand-binding-domain association is preserved. As proof of principle, we redesign a cross-reactive regulator: replacing its DNA-binding domain with one from an orthogonal regulator abolishes unwanted promoter crosstalk while preserving ligand-inducible activation of its own target, transferring orthogonality to a previously incompatible pair. Together, natural-diversity screening and domain swapping emerge as complementary routes to expand LTTR biosensor repertoires, revealing a strong link between connector architecture and chimera function.

Methods for installing synthetic functions on living cell surfaces provide powerful approaches for imaging, sensing, and manipulating cell behavior, but many require genetic modification of the target cell or chemical modification of the plasma membrane. Here, we repurpose the glycosylphosphatidylinositol-anchored protein (GPI-AP)-binding toxin aerolysin as a modular chassis for non-genetic cell-surface functionalization. We show that a non-cytotoxic, monomeric aerolysin mutant retains high-affinity and GPI-AP-dependent cell binding when genetically fused to diverse protein cargos. Fluorescent protein-aerolysin fusions robustly label multiple cell types and remain predominantly associated with the cell surface for at least 24 h, in contrast to wheat germ agglutinin, which is extensively internalized. Aerolysin can also be equipped with SpyTag/SpyCatcher to enable modular assembly with independently expressed protein cargos. Importantly, aerolysin supports functional rather than solely optical modification of the cell surface: fusion to the proximity-labeling enzyme APEX2 enables extracellular protein biotinylation, while fusion to HUH endonuclease tags enables covalent attachment of synthetic DNA to living cells. Using this latter architecture, we developed a DNA hairpin sensor that converts cell-surface nuclease activity into a fluorescent signal and distinguishes cells with different levels of extracellular nuclease activity. Together, these results establish non-cytotoxic aerolysin as a genetically encoded, soluble adapter for installing proteins, enzymes, and programmable nucleic acids onto living cells without modification of the target-cell genome.

Lysine acylations, including lactylation (Klac), are pivotal regulators of cellular physiology. However, their analysis is currently bottlenecked by antibody enrichment strategies that suffer from sequence bias and require milligram-scale protein inputs, severely precluding the profiling of scarce clinical biopsies and rare cell populations. Here we present ChemIntelligence, an acyl-NHS chemistry-empowered derivatization strategy that rapidly generates unprecedented acylation-specific spectral libraries, exemplified by over 2.5x10^9 human Klac peptides, enabling cross-species reference atlases. Integrated with Prosit-based rescoring, these libraries substantially increase Klac identifications across diverse proteomic datasets. Leveraging this spectral resource, we devised ChemIntelligence Scope, a reproducible, multiplexed parallel reaction monitoring (PRM) platform that quantifies hundreds of Klac peptides per injection from as little as ~200 ng of cell lysates, clinical biopsies, and even true single cells - revealing functional Klac signatures inaccessible to conventional methods. The ChemIntelligence pipeline also extends seamlessly to lysine nicotinylation, underscoring its broad adaptability for discovering and profiling new acylations. Together, these chemical and computational advances establish a scalable, antibody-free framework for acyl-proteome mapping that overcomes input constraints and enables deep functional insights from otherwise intractable biological samples.

Membrane proteins achieve a remarkable range of cellular functions, yet their characterization at high throughputs remains difficult with standard reconstitution methods. Here, we develop On-bead Reconstitution into Bilayers via Cell-free Transcription and Translation (ORB-TXTL), a platform that uses compositionally tunable lipid bilayer-coated silica beads as scaffolds for cell-free synthesized interacting and integral membrane proteins. ORB-TXTL is fast as it just takes a few hours to integrate membrane proteins onto the beads, which can be extensively washed and seamlessly transferred between reaction buffers, to perform assays that are read out by standard laboratory equipment without tagging and sophisticated equipment. We first characterized the lipid interactions of the mechanosensitive channel MscL, then screened 169 E. coli proteins and identified a systematic dependence of membrane integration efficiency on the number of transmembrane domains. Finally, we functionally reconstituted the E. coli phospholipid synthesis pathway, demonstrating that ORB-TXTL is a tractable and cheap chassis for multi-enzyme membrane biochemistry.

O-GlcNAcylation is an important post translational modification that regulates numerous cellular processes, yet tools enabling selective removal of O GlcNAc from individual proteins via endogenous O-GlcNAcase (OGA) in living cells remain limited. Here, we report De-O GlcNAcylation-targeting chimeras (DOGTACs), a chemically induced proximity strategy that selectively reduces O GlcNAc from target proteins by recruiting endogenous OGA. Initial designs incorporating potent competitive OGA inhibitors efficiently engaged OGA but failed to induce de-O-GlcNAcylation, revealing that catalytic competence is essential for productive proximity-driven editing. By attenuating inhibitor potency while retaining sufficient OGA engagement, we developed optimized DOGTACs that promote concentration- and time-dependent, target-specific de-O-GlcNAcylation in living cells without perturbing global O-GlcNAc levels. Furthermore, we successfully applied DOGTAC to additional target proteins across multiple cell lines. Collectively, this work established attenuated competitive inhibitors as effective recruitment modules for catalytic enzyme engagement and a novel framework, DOGTAC, for targeted de-O-GlcNAcylation via endogenous OGA recruitment in living cells.

Chemical proteomics can provide global portraits of small molecule-protein interactions in native biological systems. Such ligandability maps have, however, been mostly restricted to readily accessible cell lines and primary immune cells. Here, we describe an activity-based protein profiling (ABPP) strategy for mapping the covalent ligandability of primary brain cells isolated from mice. By investigating sets of stereochemically defined electrophilic small molecules (stereoprobes), we identify liganding events for diverse brain cell proteins, including many with nervous system-enriched expression. In this category were multiple hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels, which we show are covalently liganded by tryptoline acrylamide stereoprobes at a conserved cysteine in their cyclic nucleotide-binding domain. The stereoprobes were found to block cAMP-dependent shifts in voltage dependence while sparing basal activity of HCN channels. We thus describe an advanced ABPP platform for identifying ligands targeting nervous system-enriched proteins, including chemical probes that modulate HCN channel function in cells.

Transcription factors remain among the most challenging therapeutic targets in part because they lack well-defined ligandable binding pockets. We recently showed that aberrantly reactive cysteines in transcription factors can be directly targeted with electrophilic small molecules to induce selective transcription factor destabilization and degradation. Here, we extend this strategy to the lineage-defining oncogenic transcription factor PAX8, a critical driver of ovarian cancer. Screening of a chemically diverse library of more than 3,000 cysteine-reactive compounds against an endogenously HiBiT-tagged PAX8 reporter identified a sulfinyl aziridine chemotype that selectively reduced PAX8 abundance. Structure-activity and stereochemical analyses revealed highly enantio- and diastereoselective activity, identifying KL6-159A as the lead compound. Quantitative proteomics demonstrated selective loss of PAX8, while cellular thermal shift analysis and chemoproteomic profiling established direct covalent engagement of PAX8 at cysteine C57. Mutation of C57 completely abolished KL6-159A-induced PAX8 depletion, demonstrating that this residue is essential for compound activity. Transcriptomic profiling revealed broad suppression of the PAX8 transcriptional program, with FOXM1 emerging as the most significantly downregulated regulatory network together with numerous established PAX8 target genes. Collectively, these studies establish direct covalent engagement, transcriptional inhibition, and destabilization of PAX8 and further demonstrate the generality of covalent chemoproteomic approaches for drugging previously intractable transcription factors.

As central executioners of cell death, caspases that activate exclusively in diseased cells would provide powerful and specific therapeutic agents. Natural caspase regulation exhibits two universal features that facilitate the engineering of such caspases: proximity-induced subunit assembly and modular separation of substrate recruitment from catalysis. Here, we take advantage of these features to engineer "Raspases," split effector caspases that conditionally reconstitute active complexes upon detection of mutant Ras, an oncogene altered in roughly a quarter of all cancers. When delivered as mRNA in lipid nanoparticles, Raspases selectively eliminate Ras-mutant human cancer lines while sparing wild-type cells. The system is built entirely from human protein domains, can be encoded as a single polyprotein, and can be adapted to trigger pyroptosis. Critically, Raspases match or exceed the potency of alternative Ras-targeting interventions in vitro. These results establish retargeted caspases as a generalizable sense-and-kill platform for selective elimination of diseased cells.

Protein aggregation disrupts proteostasis and drives neurodegeneration. Hsp104 is a hexameric, ring-shaped AAA+ ATPase that dissolves protein aggregates, yet how hexamers translocate and extract polypeptides trapped in mechanically resistant aggregates remains unclear. Using substrates that recapitulate the physical constraints of aggregates, we establish that Hsp104 is a processive, bidirectional translocase that can dynamically switch direction while threading a single polypeptide. On mechanically restrained substrates and prions, Hsp104 hexamers execute biased stochastic transitions among three conformational states at individual interprotomer interfaces: closed, extended, and a previously unobserved hyperextended form. These transitions follow kinetically favored paths rather than a rigid rotary sequence. The resulting biased stochastic stepping, enabled by the conformational plasticity of Hsp104 hexamers, underpins operational adaptability and redefines the functional logic of AAA+ motors.

Targeted protein degradation (TPD) offers a route to eliminate disease-driving proteins that remain inaccessible to conventional inhibitors. However, degrader discovery remains low-throughput, labor-intensive, and dependent on randomized libraries or non-human display systems, limiting functional selection in mammalian cells. Here, we present a high-throughput, human cell-based platform for screening peptide-guided ubiquibodies (uAbs). These genetically encodable, doxycycline-inducible degraders fuse peptide guides generated by protein language models to the CHIP{Delta}TPR E3 ligase domain, creating a modular, CRISPR-like system for programmable TPD. For each target, we introduce a pooled uAb library into the corresponding fluorescent reporter cell line, isolate cells with reduced target abundance by FACS, and recover enriched peptide guides by sequencing. For {beta}-catenin, enriched uAbs reduced endogenous {beta}-catenin abundance and Wnt signaling in DLD1 cells. GFAP-directed uAbs reduced endogenous GFAP abundance and cell viability in U251 glioblastoma cells, while EWS::FLI1-directed uAbs reduced fusion oncoprotein abundance, suppressed EWSAT1 expression, and increased apoptosis in Ewing sarcoma models. Finally, a screen using endogenously tagged GATA2 further identified uAbs that reduced GATA2 under native genomic regulation. Overall, our platform connects generative peptide design to functional mammalian selection and establishes a scalable strategy for CRISPR-like proteome perturbation.

Protein degradation regulates cellular homeostasis, yet many degradation events are difficult to study because they lack a readily selectable phenotype. Here, we develop Degradation-Induced Pyroptosis TArgeting Receptors (DIPTAR), a modular synthetic biology platform that couples protein degradation to CARD8-mediated pyroptosis. Using HIF-1 as a model substrate, we show that DIPTAR faithfully reports oxygen-dependent VHL-mediated degradation and enables pooled CRISPR screening to identify established and previously unrecognized regulators of HIF-1 stability. DIPTAR is functional across multiple cell types and can be programmed with diverse proteins, including BRD4, I{kappa}B, and p53, to convert distinct degradation stimuli into a common pyroptotic output. DIPTAR also detects pathogen-mediated perturbations of host degradation pathways, including both inhibition and induction of degradation-dependent signaling. By converting protein degradation into a robust selectable phenotype, DIPTAR provides a scalable platform for functional genetic discovery, interrogation of degradation pathways, degrader characterization, and investigation of host-pathogen interactions.

Isopeptide bonds are amide bonds between amino acid side chains that can form autocatalytically, notably in the pili of Gram-positive bacteria. Here, we design de novo proteins that form both intramolecular and intermolecular isopeptide bonds entirely autocatalytically. We report over 50 designs that form isopeptide bonds, validated by mass spectrometry and 5 crystal structures. We redesign these constructs as split proteins that form a covalent intermolecular isopeptide crosslink when combined. These split designs are orthogonal to the existing isopeptide-based SpyTag/Catcher system, and their formation can be regulated by temperature, providing control over the timing of crosslinking in protein assemblies. We extend these designs to create rigid domain crosslinks that enable the construction of large well ordered symmetric rings of up to 215 kDa that are irreversibly covalently crosslinked by multiple isopeptide bonds into a single molecule. Our results provide insight into the determinants of isopeptide bond formation, considerably expand the set of isopeptide bond crosslinking systems, and establish a framework to construct fully covalent rigid protein assemblies.

O-linked {beta}-N-acetylglucosamine (O-GlcNAc) transferase (OGT) is the sole writer for intracellular O-GlcNAcylation. It catalyzes O-GlcNAcylation of thousands of protein substrates, but relatively less is known about the post-translational modifications that occur on OGT itself. Herein, we demonstrate that OGT is S-palmitoylated at Cys-472 and Cys-477, which is mediated by the S-acyltransferase Zinc Finger DHHC-Type Palmitoyl transferase 14 (zDHHC14) and removed by acyl protein thioesterase 2 (APT2). S-Palmitoylation stabilizes OGT by shunting it away from the lysosomal chaperone-mediated autophagy (CMA) pathway, as S-palmitoylation decreases the interaction between OGT and heat shock cognate 70 kDa protein (HSC70), the CMA chaperone. Via label-free quantitative mass spectrometry, we find that S- palmitoylation elevates the affinity between OGT and protein phosphatase 1 catalytic subunit gamma (PPP1CC), but not PPP1CB. We further demonstrate that S-palmitoylation of OGT augments binding with Yes-associated protein-1 (YAP), a protein that associates with PPP1CC, and subsequently enhances YAP O-GlcNAcylation. Our work unearths S-palmitoylation of OGT and CMA-mediated degradation of lysosomal OGT, the orchestration of which finetunes the activity of key OGT complexes, such as OGT-PPP1CC, and contributes to OGT substrate selectivity.

Skeletal rearrangement drives the immense structural complexity of terpene, yet predicting it remains a formidable challenge due to sequence-function decoupling in terpene synthases. Here, we established TRACER (terpene rearrangement annotation via co-attentive enzyme-product representation), a multimodal framework mapping the latent associations between sequence-derived enzyme representations and product chemotypes. Retrospective validation proved TRACERs exceptional precision in predicting compound classes and discriminating skeletal rearrangement (SR) from non-skeletal rearrangement (NSR) pathways. TRACER-guided genome mining characterized two bifunctional synthases, FsPS and AcPS, uncovering four unprecedented carbon skeletons. Density functional theory calculations deciphered these cyclization cascades, pinpointing a critical 5/6/11 tricyclic intermediate as the key branching node for scaffold diversification. Mutagenesis and molecular dynamics simulations suggested that E305 in FsPS enables rearrangement by maintaining active-site water exclusion, whereas its alanine mutation causes premature carbocation quenching. Collectively, this work establishes a predictive paradigm for the rational discovery and mechanistic elucidation of complex terpene architectures.

Deubiquitinase-targeting chimeras (DUBTACs) have emerged as a promising strategy for targeted protein stabilization, but their broader application remains limited by the scarcity of ligandable deubiquitinase recruiters. Here, we report a previously unexplored four-membered-ring OTUB1 recruiter chemotype. Through systematic structure-activity relationship studies, we identified compound 21 (MS2159) as a potent and selective covalent OTUB1 ligand. Biochemical and intact protein mass spectrometric analyses demonstrated that MS2159 selectively engages the non-catalytic C23 residue of OTUB1, shows minimal reactivity toward other tested proteins, and preserves OTUB1 deubiquitinase activity. Conjugation of MS2159 with the CFTR ligand lumacaftor yielded compound 25 (MS2134), which effectively stabilized {Delta}F508-CFTR. Collectively, these findings establish a new OTUB1 recruiter scaffold, expand the ligandable chemical space of OTUB1, and provide additional opportunities for developing next-generation DUBTACs.

The majority of metabolic pathways rely on the production of activated electrophilic intermediates, e.g., coenzyme-A esters, and their chemical structures and abundances are central to understanding enzyme function and biochemical mechanisms. However, most electrophilic metabolites are lost in traditional metabolomic analysis and thus remain poorly characterized. Here we introduce a biochemical probe, O-(trimethylammoniobutyl)-hydroxylamine (TAMOHA), that enables comprehensive profiling of electrophilic species such as coenzyme-A esters, ketones, and aldehydes. TAMOHA incorporates a highly nucleophilic hydroxyl amine that reacts quickly with electrophilic species upon tissue lysis, trapping them as stable derivatives that feature a tetraalkylammonium moiety whose constitutive charge and characteristic MS2 fragmentation fingerprint enable their highly sensitive detection. Using TAMOHA to survey the electrophilomes of E. coli, C. elegans, and mouse revealed several thousand electrophilic metabolites, most of which have not been characterized. We then demonstrate trapping of electrophilic metabolites with TAMOHA in the context of specific biochemical pathways, confirming previously proposed functions of two fatty acid metabolism enzymes, detecting formaldehyde production in mice, and providing new insights into the biosynthesis of ascaroside pheromones in C. elegans. We anticipate that use of TAMOHA for the profiling of electrophilic species will help clarify enzyme function and uncover previously elusive biochemical mechanisms in a wide range of biological systems. Table of Contents artwork O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=106 SRC="FIGDIR/small/743530v1_ufig1.gif" ALT="Figure 1"> View larger version (47K): org.highwire.dtl.DTLVardef@199c060org.highwire.dtl.DTLVardef@12516d7org.highwire.dtl.DTLVardef@1fe81f1org.highwire.dtl.DTLVardef@5277a_HPS_FORMAT_FIGEXP M_FIG C_FIG

Riboswitches regulate gene expression in response to ligand binding, remodeling their secondary structure to terminate transcription or block translation. This innate switching has driven efforts to repurpose riboswitches as synthetic control elements. Although promising, tuning riboswitch responses to new ligands and functions has proven difficult. Large RNAs such as the ribosome and RNase P exhibit an alternative switching mode via the docking and undocking of tertiary contacts. These transitions are buried deep within the machines, and there is no minimal system to study them in isolation. To overcome this limitation, we built a minimal 3D-structure ligand-inducible switch. We started with a previously designed nanostructure containing an ATP-aptamer and a tetraloop/tetraloop receptor (TL/TLR) tertiary contact. DMS-MaPseq screening of 3,375 mutants of the two linking motifs, a kink-turn and a 4-1 junction, identified 237 variants in which AMP binding undocked the TL/TLR and 120 in which it drove docking. Switching arose almost entirely from mutations in the conserved sheared G{middle dot}A base pairs of the kink-turn. Fitting four representative constructs AMP titrations to a linked-equilibrium model yielded coupling free energies spanning 3.7 kcal/mol, and magnesium titrations with and without AMP independently confirmed these couplings while revealing a three-state docking pathway in mutants lacking wild-type coupling. Single nucleotides inserted into the kink-turn motif adjust the sign and strength of coupling without redesigning the secondary structure. This simple system thus provides a platform both as a model for tertiary switching in other large RNA machines and as a foundation for designing synthetic control elements based on tertiary interactions.