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The papain-like protease PLpro is an essential coronavirus enzyme that is required for processing viral polyproteins to generate a functional replicase complex and enable viral spread 1 , 2 . PLpro is also implicated in cleaving proteinaceous post-translational modifications on host proteins as an evasion mechanism against host antiviral immune responses 3 – 5 . Here we perform biochemical, structural and functional characterization of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) PLpro (SCoV2-PLpro) and outline differences with SARS-CoV PLpro (SCoV-PLpro) in regulation of host interferon and NF-κB pathways. SCoV2-PLpro and SCoV-PLpro share 83% sequence identity but exhibit different host substrate preferences; SCoV2-PLpro preferentially cleaves the ubiquitin-like interferon-stimulated gene 15 protein (ISG15), whereas SCoV-PLpro predominantly targets ubiquitin chains. The crystal structure of SCoV2-PLpro in complex with ISG15 reveals distinctive interactions with the amino-terminal ubiquitin-like domain of ISG15, highlighting the high affinity and specificity of these interactions. Furthermore, upon infection, SCoV2-PLpro contributes to the cleavage of ISG15 from interferon responsive factor 3 (IRF3) and attenuates type I interferon responses. Notably, inhibition of SCoV2-PLpro with GRL-0617 impairs the virus-induced cytopathogenic effect, maintains the antiviral interferon pathway and reduces viral replication in infected cells. These results highlight a potential dual therapeutic strategy in which targeting of SCoV2-PLpro can suppress SARS-CoV-2 infection and promote antiviral immunity. Biochemical, structural and functional studies on the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) papain-like protease PLpro reveal that it regulates host antiviral responses by preferentially cleaving the ubiquitin-like interferon-stimulated gene 15 protein (ISG15) and identify this protease as a potential therapeutic target for coronavirus disease 2019 (COVID-19).

The large family of deubiquitinating enzymes (DUBs) are involved in the regulation of a plethora of processes carried out inside the cell by protein ubiquitination. Ubiquitination is a basic pathway responsible for the correct protein homeostasis in the cell, which could regulate the fate of proteins through the ubiquitin–proteasome system (UPS). In this review we will focus on recent advances on the molecular mechanisms and specificities found for some types of DUBs enzymes, highlighting illustrative examples in which the regulatory mechanism for DUBs has been understood in depth at the molecular level by structural biology. DUB proteases are responsible for cleavage and regulation of the multiple types of ubiquitin linkages that can be synthesized inside the cell, known as the ubiquitin-code, which are tightly connected to specific substrate functions. We will display some strategies carried out by members of different DUB families to provide specificity on the cleavage of particular ubiquitin linkages. Finally, we will also discuss recent progress made for the development of drug compounds targeting DUB proteases, which are usually correlated to the progress of many pathologies such as cancer and neurodegenerative diseases.

The structures of the deubiquitinating enzyme Cezanne alone or in complex with its substrate or product are solved, showing how Cezanne specifically targets Lys11-linked polyubiquitin. Cezanne (OTUD7B) structure and function The small modifier protein ubiquitin can bind to many other proteins either individually or in polyubiquitin chains, regulating a variety of cellular processes. The eight different linkage types between ubiquitin molecules within polyubiquitin chains constitute the 'ubiquitin code', as the linkages are independently regulated resulting in different fates of the substrate proteins. David Komander and colleagues investigate how the deubiquitinating enzyme Cezanne (also known as OTUD7B) specifically targets Lys11-linked polyubiquitin by solving the structures of this enzyme alone and in complexes with its substrate and product. The study is noteworthy not only for providing mechanistic insights into ubiquitin-mediated conformational changes in Cezanne that activate it only in context of Lys11-linked polyubiquitin, but also for developing innovative tools that should be of use for future analyses of ubiquitin signalling. The post-translational modification of proteins with polyubiquitin regulates virtually all aspects of cell biology. Eight distinct chain linkage types co-exist in polyubiquitin and are independently regulated in cells. This ‘ubiquitin code’ determines the fate of the modified protein 1 . Deubiquitinating enzymes of the ovarian tumour (OTU) family regulate cellular signalling by targeting distinct linkage types within polyubiquitin 2 , and understanding their mechanisms of linkage specificity gives fundamental insights into the ubiquitin system. Here we reveal how the deubiquitinase Cezanne (also known as OTUD7B) specifically targets Lys11-linked polyubiquitin. Crystal structures of Cezanne alone and in complex with monoubiquitin and Lys11-linked diubiquitin, in combination with hydrogen–deuterium exchange mass spectrometry, enable us to reconstruct the enzymatic cycle in great detail. An intricate mechanism of ubiquitin-assisted conformational changes activates the enzyme, and while all chain types interact with the enzymatic S1 site, only Lys11-linked chains can bind productively across the active site and stimulate catalytic turnover. Our work highlights the plasticity of deubiquitinases and indicates that new conformational states can occur when a true substrate, such as diubiquitin, is bound at the active site.

Serine hydroxymethyltransferase 2 (SHMT2) regulates one-carbon transfer reactions that are essential for amino acid and nucleotide metabolism, and uses pyridoxal-5′-phosphate (PLP) as a cofactor. Apo SHMT2 exists as a dimer with unknown functions, whereas PLP binding stabilizes the active tetrameric state. SHMT2 also promotes inflammatory cytokine signalling by interacting with the deubiquitylating BRCC36 isopeptidase complex (BRISC), although it is unclear whether this function relates to metabolism. Here we present the cryo-electron microscopy structure of the human BRISC–SHMT2 complex at a resolution of 3.8 Å. BRISC is a U-shaped dimer of four subunits, and SHMT2 sterically blocks the BRCC36 active site and inhibits deubiquitylase activity. Only the inactive SHMT2 dimer—and not the active PLP-bound tetramer—binds and inhibits BRISC. Mutations in BRISC that disrupt SHMT2 binding impair type I interferon signalling in response to inflammatory stimuli. Intracellular levels of PLP regulate the interaction between BRISC and SHMT2, as well as inflammatory cytokine responses. These data reveal a mechanism in which metabolites regulate deubiquitylase activity and inflammatory signalling. Cryo-electron microscopy and mutation experiments demonstrate that the inactive SHMT2 dimer—and not the pyridoxal-5′-phosphate-bound tetramer—binds to BRISC, which reveals a mechanism for the regulation of deubiquitylases and inflammatory signalling.

Activity-based probes (ABPs) are widely used to monitor the activity of enzyme families in biological systems. Inferring enzyme activity from probe reactivity requires that the probe reacts with the enzyme at its active site; however, probe-labeling sites are rarely verified. Here we present an enhanced chemoproteomic approach to evaluate the activity and probe reactivity of deubiquitinase enzymes, using bioorthogonally tagged ABPs and a sequential on-bead digestion protocol to enhance the identification of probe-labeling sites. We confirm probe labeling of deubiquitinase catalytic Cys residues and reveal unexpected labeling of deubiquitinases on non-catalytic Cys residues and of non-deubiquitinase proteins. In doing so, we identify ZUFSP (ZUP1) as a previously unannotated deubiquitinase with high selectivity toward cleaving K63-linked chains. ZUFSP interacts with and modulates ubiquitination of the replication protein A (RPA) complex. Our reactive-site-centric chemoproteomics method is broadly applicable for identifying the reaction sites of covalent molecules, which may expand our understanding of enzymatic mechanisms. Deubiquitinases are proteases that cleave after the C-terminus of ubiquitin to hydrolyze ubiquitin chains and cleave ubiquitin from substrates. Here the authors describe a reactive-site-centric chemoproteomics approach to studying deubiquitinase activity, and expand the repertoire of known deubiquitinases.

The deubiquitylating enzymes (DUBs, also known as deubiquitylases or deubiquitinases) maintain the dynamic state of the cellular ubiquitome by releasing conjugated ubiquitin from proteins. In light of the many cellular functions of ubiquitin, DUBs occupy key roles in almost all aspects of cell behaviour. Many DUBs show selectivity for particular ubiquitin linkage types or positions within ubiquitin chains. Others show chain-type promiscuity but can select a distinct palette of protein substrates via specific protein–protein interactions established through binding modules outside of the catalytic domain. The ubiquitin chain cleavage mode or chain linkage specificity has been related directly to biological functions. Examples include regulation of protein degradation and ubiquitin recycling by the proteasome, DNA repair pathways and innate immune signalling. DUB cleavage specificity is also being harnessed for analysis of ubiquitin chain architecture that is assembled on specific proteins. The recent development of highly specific DUB inhibitors heralds their emergence as a new class of therapeutic targets for numerous diseases.By opposing protein ubiquitylation, deubiquitylating enzymes (DUBs) regulate various cellular processes, including protein degradation, the DNA damage response, cell signalling and autophagy. Many DUBs show high specificity for ubiquitin chain architecture and/or the protein substrate that they recognize, and have emerged as exciting therapeutic targets within the field of proteostasis.

Many diseases are driven by proteins that are aberrantly ubiquitinated and degraded. These diseases would be therapeutically benefited by targeted protein stabilization (TPS). Here we present deubiquitinase-targeting chimeras (DUBTACs), heterobifunctional small molecules consisting of a deubiquitinase recruiter linked to a protein-targeting ligand, to stabilize the levels of specific proteins degraded in a ubiquitin-dependent manner. Using chemoproteomic approaches, we discovered the covalent ligand EN523 that targets a non-catalytic allosteric cysteine C23 in the K48-ubiquitin-specific deubiquitinase OTUB1. We showed that a DUBTAC consisting of our EN523 OTUB1 recruiter linked to lumacaftor, a drug used to treat cystic fibrosis that binds ΔF508-cystic fibrosis transmembrane conductance regulator (CFTR), robustly stabilized ΔF508-CFTR protein levels, leading to improved chloride channel conductance in human cystic fibrosis bronchial epithelial cells. We also demonstrated stabilization of the tumor suppressor kinase WEE1 in hepatoma cells. Our study showcases covalent chemoproteomic approaches to develop new induced proximity-based therapeutic modalities and introduces the DUBTAC platform for TPS.A targeted protein stabilization platform termed deubiquitinase-targeting chimera (DUBTAC) was developed based on heterobifunctional small molecules consisting of a deubiquitinase OTUB1 recruiter linked to a protein-targeting ligand.

Cervical cancer (CC) remains a major global gynecological malignancy, with a rising incidence among younger women in specific regions. Human papillomavirus (HPV) screening and cytological examination have markedly reduced the disease burden; nonetheless, tumor progression, therapeutic resistance and recurrence continue to pose major clinical challenges. Thus, elucidating the molecular mechanisms underlying the progression of CC is crucial. Deubiquitinating enzymes (DUBs) regulate ubiquitin-dependent protein turnover and signaling, emerging as vital modulators of cell cycle progression, DNA damage response, apoptosis, immune regulation and HPV-associated carcinogenesis. Notably, DUBs facilitate CC progression by stabilizing oncogenic proteins, regulating tumor suppressors and modulating major signaling pathways. In addition, several DUBs are closely associated with radiosensitivity, chemoresistance and potential targeted therapeutic strategies. The present review summarizes the molecular mechanisms and therapeutic implications of DUBs in CC, while discussing their translational value for future clinical applications.

is a major apicomplexan pathogen responsible for significant reproductive losses in livestock, yet lacks effective therapeutics. Here, we identify and functionally characterize a previously unstudied OTU-like deubiquitinase (ncOTU; XP_003886403) as a key modulator of host-pathogen interactions. Sequence and structural analyses revealed conservation of the catalytic triad (D257, C260, H362) and a Y305-W315-G316 inhibition pocket analogous to viral OTU proteases. Recombinant ncOTU exhibited robust deubiquitinase activity and significantly reduced global ubiquitination levels in mammalian cells, preferentially targeting mono-ubiquitinated and low-molecular-weight substrates. Transcriptomic analysis demonstrated that ncOTU expression correlates with suppressed NF-κB signaling, type I interferon responses, and downstream antiviral effectors, while partially uncoupling upstream nucleic acid sensing pathways. Structure-based virtual screening and biochemical validation identified multiple small-molecule inhibitors targeting the conserved inhibition pocket. Dose-response analysis revealed submicromolar potency for ncOTUi-9 (IC = 0.1 μM), ncOTUi-8 (0.2 μM), and ncOTUi-19 (0.3 μM), whereas ncOTUi-3 showed lower activity (7.1 μM). Interaction analyses confirmed stable binding within the inhibition pocket, with more extensive contact networks correlating with increased potency. Collectively, these findings establish ncOTU as a functional deubiquitinase that contributes to evasion and highlight it as a promising therapeutic target for neosporosis.

Deubiquitinating enzymes (DUBs) regulate ubiquitin signaling by trimming ubiquitin chains or removing ubiquitin from modified substrates. Similar activities exist for ubiquitin-related modifiers, although the enzymes involved are usually not related. Here, we report human ZUFSP (also known as ZUP1 and C6orf113) and fission yeast Mug105 as founding members of a DUB family different from the six known DUB classes. The crystal structure of human ZUFSP in covalent complex with propargylated ubiquitin shows that the DUB family shares a fold with UFM1- and Atg8-specific proteases, but uses a different active site more similar to canonical DUB enzymes. ZUFSP family members differ widely in linkage specificity through differential use of modular ubiquitin-binding domains (UBDs). While the minimalistic Mug105 prefers K48 chains, ZUFSP uses multiple UBDs for its K63-specific endo-DUB activity. K63 specificity, localization, and protein interaction network suggest a role for ZUFSP in DNA damage response. Deubiquitinating enzymes (DUBs) are essential to modulate ubiquitin signaling. While known DUBs can be grouped into six families, the authors here present biochemical and structural evidence for a seventh DUB family, defining determinants of substrate specificity for two representative enzymes.