Modular and integrative activity reporters enhance biochemical studies in the yeast ER.

The yeast endoplasmic reticulum sequestration and screening (YESS) system is a broadly applicable platform to perform high-throughput biochemical studies of post-translational modification enzymes (PTM-enzymes). This system enables researchers to profile and engineer the activity and substrate specificity of PTM-enzymes and to discover inhibitor-resistant enzyme mutants. In this study, we expand the capabilities of YESS by transferring its functional components to integrative plasmids. The YESS integrative system yields uniform protein expression and protease activities in various configurations, allows one to integrate activity reporters at two independent loci and to split the system between integrative and centromeric plasmids. We characterize these integrative reporters with two viral proteases, Tobacco etch virus (TEVp) and 3-chymotrypsin like protease (3CLpro), in terms of coefficient of variance, signal-to-noise ratio and fold-activation. Overall, we provide a framework for chromosomal-based studies that is modular, enabling rigorous high-throughput assays of PTM-enzymes in yeast.

Combined effect of SAR-endolysin LysKpV475 with polymyxin B and Salmonella bacteriophage phSE-5.

Endolysins are bacteriophage (or phage)-encoded enzymes that catalyse the peptidoglycan breakdown in the bacterial cell wall. The exogenous action of recombinant phage endolysins against Gram-positive organisms has been extensively studied. However, the outer membrane acts as a physical barrier when considering the use of recombinant endolysins to combat Gram-negative bacteria. This study aimed to evaluate the antimicrobial activity of the SAR-endolysin LysKpV475 against Gram-negative bacteria as single or combined therapies, using an outer membrane permeabilizer (polymyxin B) and a phage, free or immobilized in a pullulan matrix. In the first step, the endolysin LysKpV475 in solution, alone and combined with polymyxin B, was tested in vitro and in vivo against ten Gram-negative bacteria, including highly virulent strains and multidrug-resistant isolates. In the second step, the lyophilized LysKpV475 endolysin was combined with the phage phSE-5 and investigated, free or immobilized in a pullulan matrix, against Salmonella enterica subsp. enterica serovar Typhimurium ATCC 13311. The bacteriostatic action of purified LysKpV475 varied between 8.125 µg ml-1 against Pseudomonas aeruginosa ATCC 27853, 16.25 µg ml-1 against S. enterica Typhimurium ATCC 13311, and 32.50 µg ml-1 against Klebsiella pneumoniae ATCC BAA-2146 and Enterobacter cloacae P2224. LysKpV475 showed bactericidal activity only for P. aeruginosa ATCC 27853 (32.50 µg ml-1) and P. aeruginosa P2307 (65.00 µg ml-1) at the tested concentrations. The effect of the LysKpV475 combined with polymyxin B increased against K. pneumoniae ATCC BAA-2146 [fractional inhibitory concentration index (FICI) 0.34; a value lower than 1.0 indicates an additive/combined effect] and S. enterica Typhimurium ATCC 13311 (FICI 0.93). A synergistic effect against S. enterica Typhimurium was also observed when the lyophilized LysKpV475 at ⅔ MIC was combined with the phage phSE-5 (m.o.i. of 100). The lyophilized LysKpV475 immobilized in a pullulan matrix maintained a significant Salmonella reduction of 2 logs after 6 h of treatment. These results demonstrate the potential of SAR-endolysins, alone or in combination with other treatments, in the free form or immobilized in solid matrices, which paves the way for their application in different areas, such as in biocontrol at the food processing stage, biosanitation of food contact surfaces and biopreservation of processed food in active food packing.

USP19 regulates DNA methylation damage repair and confers temozolomide resistance through MGMT stabilization.

OBJECTIVE: To elucidate the relationship between USP19 and O(6)-methylguanine-DNA methyltransferase (MGMT) after temozolomide treatment in glioblastoma (GBM) patients with chemotherapy resistance. METHODS: Screening the deubiquitinase pannel and identifying the deubiquitinase directly interacts with and deubiquitination MGMT. Deubiquitination assay to confirm USP19 deubiquitinates MGMT. The colony formation and tumor growth study in xenograft assess USP19 affects the GBM sensitive to TMZ was performed by T98G, LN18, U251, and U87 cell lines. Immunohistochemistry staining and survival analysis were performed to explore how USP19 is correlated to MGMT in GBM clinical management. RESULTS: USP19 removes the ubiquitination of MGMT to facilitate the DNA methylation damage repair. Depletion of USP19 results in the glioblastoma cell sensitivity to temozolomide, which can be rescued by overexpressing MGMT. USP19 is overexpressed in glioblastoma patient samples, which positively correlates with the level of MGMT protein and poor prognosis in these patients. CONCLUSION: The regulation of MGMT ubiquitination by USP19 plays a critical role in DNA methylation damage repair and GBM patients' temozolomide chemotherapy response.

X-ray structure and mutagenesis analyses of Clostridioides difficile endolysin Ecd09610 glucosaminidase domain.

Clostridioides difficile endolysin (Ecd09610) consists of an unknown domain at its N terminus, followed by two catalytic domains, a glucosaminidase domain and endopeptidase domain. X-ray structure and mutagenesis analyses of the Ecd09610 catalytic domain with glucosaminidase activity (Ecd09610CD53) were performed. Ecd09610CD53 was found to possess an α-bundle-like structure with nine helices, which is well conserved among GH73 family enzymes. The mutagenesis analysis based on X-ray structures showed that Glu405 and Asn470 were essential for enzymatic activity. Ecd09610CD53 may adopt a neighboring-group mechanism for a catalytic reaction in which Glu405 acted as an acid/base catalyst and Asn470 helped to stabilize the oxazolinium ion intermediate. Structural comparisons with the newly identified Clostridium perfringens autolysin catalytic domain (AcpCD) in the P1 form and a zymography analysis demonstrated that AcpCD was 15-fold more active than Ecd09610CD53. The strength of the glucosaminidase activity of the GH73 family appears to be dependent on the depth of the substrate-binding groove.

Circulating soluble fibroblast activation protein (FAP) levels are independent of cardiac and extra-cardiac FAP expression determined by targeted molecular imaging in patients with myocardial FAP activation.

INTRODUCTION: Tissue Fibroblast Activation Protein alpha (FAP) is overexpressed in various types of acute and chronic cardiovascular disease. A soluble form of FAP has been detected in human plasma, and low circulating FAP concentrations are associated with increased risk of death in patients with acute coronary syndrome. However, little is known about the regulation and release of FAP from fibroblasts, and whether circulating FAP concentration is associated with tissue FAP expression. This study characterizes the release of FAP in human cardiac fibroblasts (CF) and analyzes the association of circulating FAP concentrations with in vivo tissue FAP expression in patients with acute (ST-segment elevation myocardial infarction, STEMI) and chronic (severe aortic stenosis, AS) myocardial FAP expression. METHODS AND RESULTS: FAP was released from CF in a time- and concentration-dependent manner. FAP concentration was higher in supernatant of TGFß-stimulated CF, and correlated with cellular FAP concentration. Inhibition of metallo- and serine-proteases diminished FAP release in vitro. Median FAP concentrations of patients with acute (77 ng/mL) and chronic (75 ng/mL, p = 0.50 vs. STEMI) myocardial FAP expression did not correlate with myocardial nor extra-myocardial nor total FAP volume (P ≥ 0.61 in all cases) measured by whole-body FAP-targeted positron emission tomography. CONCLUSION: We describe a time- and concentration dependent, protease-mediated release of FAP from cardiac fibroblasts. Circulating FAP concentrations were not associated with increased in vivo tissue FAP expression determined by molecular imaging in patients with both chronic and acute myocardial FAP expression. These data suggest that circulating FAP and tissue FAP expression provide complementary, non-interchangeable information.

DoUBLing up: ubiquitin and ubiquitin-like proteases in genome stability.

Maintaining stability of the genome requires dedicated DNA repair and signalling processes that are essential for the faithful duplication and propagation of chromosomes. These DNA damage response (DDR) mechanisms counteract the potentially mutagenic impact of daily genotoxic stresses from both exogenous and endogenous sources. Inherent to these DNA repair pathways is the activity of protein factors that instigate repair processes in response to DNA lesions. The regulation, coordination, and orchestration of these DDR factors is carried out, in a large part, by post-translational modifications, such as phosphorylation, ubiquitylation, and modification with ubiquitin-like proteins (UBLs). The importance of ubiquitylation and UBLylation with SUMO in DNA repair is well established, with the modified targets and downstream signalling consequences relatively well characterised. However, the role of dedicated erasers for ubiquitin and UBLs, known as deubiquitylases (DUBs) and ubiquitin-like proteases (ULPs) respectively, in genome stability is less well established, particularly for emerging UBLs such as ISG15 and UFM1. In this review, we provide an overview of the known regulatory roles and mechanisms of DUBs and ULPs involved in genome stability pathways. Expanding our understanding of the molecular agents and mechanisms underlying the removal of ubiquitin and UBL modifications will be fundamental for progressing our knowledge of the DDR and likely provide new therapeutic avenues for relevant human diseases, such as cancer.

Genetic interaction mapping reveals functional relationships between peptidoglycan endopeptidases and carboxypeptidases.

Peptidoglycan (PG) is the main component of the bacterial cell wall; it maintains cell shape while protecting the cell from internal osmotic pressure and external environmental challenges. PG synthesis is essential for bacterial growth and survival, and a series of PG modifications are required to allow expansion of the sacculus. Endopeptidases (EPs), for example, cleave the crosslinks between adjacent PG strands to allow the incorporation of newly synthesized PG. EPs are collectively essential for bacterial growth and must likely be carefully regulated to prevent sacculus degradation and cell death. However, EP regulation mechanisms are poorly understood. Here, we used TnSeq to uncover novel EP regulators in Vibrio cholerae. This screen revealed that the carboxypeptidase DacA1 (PBP5) alleviates EP toxicity. dacA1 is essential for viability on LB medium, and this essentiality was suppressed by EP overexpression, revealing that EP toxicity both mitigates, and is mitigated by, a defect in dacA1. A subsequent suppressor screen to restore viability of ΔdacA1 in LB medium identified hypomorphic mutants in the PG synthesis pathway, as well as mutations that promote EP activation. Our data thus reveal a more complex role of DacA1 in maintaining PG homeostasis than previously assumed.

Structure-based virtual screening of novel USP5 inhibitors targeting the zinc finger ubiquitin-binding domain.

The equilibrium of cellular protein levels is pivotal for maintaining normal physiological functions. USP5 belongs to the deubiquitination enzyme (DUBs) family, controlling protein degradation and preserving cellular protein homeostasis. Aberrant expression of USP5 is implicated in a variety of diseases, including cancer, neurodegenerative diseases, and inflammatory diseases. In this paper, a multi-level virtual screening (VS) approach was employed to target the zinc finger ubiquitin-binding domain (ZnF-UBD) of USP5, leading to the identification of a highly promising candidate compound 0456-0049. Molecular dynamics (MD) simulations were then employed to assess the stability of complex binding and predict hotspot residues in interactions. The results indicated that the candidate stably binds to the ZnF-UBD of USP5 through crucial interactions with residues ARG221, TRP209, GLY220, ASN207, TYR261, TYR259, and MET266. Binding free energy calculations, along with umbrella sampling (US) simulations, underscored a superior binding affinity of the candidate relative to known inhibitors. Moreover, US simulations revealed conformational changes of USP5 during ligand dissociation. These insights provide a valuable foundation for the development of novel inhibitors targeting USP5.

Biofilm-disrupting effects of phage endolysins LysAm24, LysAp22, LysECD7, and LysSi3: breakdown the matrix.

The ability of most opportunistic bacteria to form biofilms, coupled with antimicrobial resistance, hinder the efforts to control widespread infections, resulting in high risks of negative outcomes and economic costs. Endolysins are promising compounds that efficiently combat bacteria, including multidrug-resistant strains and biofilms, without a low probability of subsequent emergence of stable endolysin-resistant phenotypes. However, the details of antibiofilm effects of these enzymes are poorly understood. To elucidate the interactions of bacteriophage endolysins LysAm24, LysAp22, LysECD7, and LysSi3 with bacterial films formed by Gram-negative species, we estimated their composition and assessed the endolysins' effects on the most abundant exopolymers in vitro. The obtained data suggests a pronounced efficiency of these lysins against biofilms with high (Klebsiella pneumoniae) and low (Acinetobacter baumannii) matrix contents, or dual-species biofilms, resulting in at least a twofold loss of the biomass. These peptidoglycan hydrolases interacted diversely with protective compounds of biofilms such as extracellular DNA and polyanionic carbohydrates, indicating a spectrum of biofilm-disrupting effects for bacteriolytic phage enzymes. Specifically, we detected disruption of acid exopolysaccharides by LysAp22, strong DNA-binding capacity of LysAm24, both of these interactions for LysECD7, and neither of them for LysSi3.

The mechanism of USP43 in the development of tumor: a literature review.

Ubiquitination of the proteins is crucial for governing protein degradation and regulating fundamental cellular processes. Deubiquitinases (DUBs) have emerged as significant regulators of multiple pathways associated with cancer and other diseases, owing to their capacity to remove ubiquitin from target substrates and modulate signaling. Consequently, they represent potential therapeutic targets for cancer and other life-threatening conditions. USP43 belongs to the DUBs family involved in cancer development and progression. This review aims to provide a comprehensive overview of the existing scientific evidence implicating USP43 in cancer development. Additionally, it will investigate potential small-molecule inhibitors that target DUBs that may have the capability to function as anti-cancer medicines.

OTUD5 promotes the growth of hepatocellular carcinoma by deubiquitinating and stabilizing SLC38A1.

BACKGROUND: Deubiquitinating enzymes (DUBs) cleave ubiquitin on substrate molecules to maintain protein stability. DUBs reportedly participate in the tumorigenesis and tumour progression of hepatocellular carcinoma (HCC). OTU deubiquitinase 5 (OTUD5), a DUB family member, has been recognized as a critical regulator in bladder cancer, breast cancer and HCC. However, the expression and biological function of OTUD5 in HCC are still controversial. RESULTS: We determined that the expression of OTUD5 was significantly upregulated in HCC tissues. High levels of OTUD5 were also detected in most HCC cell lines. TCGA data analysis demonstrated that high OTUD5 expression indicated poorer overall survival in HCC patients. OTUD5 silencing prominently suppressed HCC cell proliferation, while its overexpression markedly enhanced the proliferation of HCC cells. Mass spectrometry analysis revealed solute carrier family 38 member 1 (SLC38A1) as a candidate downstream target protein of OTUD5. Coimmunoprecipitation analysis confirmed the interaction between OTUD5 and SLC38A1. OTUD5 knockdown reduced and OTUD5 overexpression increased SLC38A1 protein levels in HCC cells. However, OTUD5 alteration had no effect on SLC38A1 mRNA expression. OTUD5 maintained SLC38A1 stability by preventing its ubiquitin-mediated proteasomal degradation. SLC38A1 silencing prominently attenuated the OTUD5-induced increase in HCC cell proliferation. Finally, OTUD5 knockdown markedly suppressed the growth of HCC cells in vivo. CONCLUSIONS: OTUD5 is an oncogene in HCC. OTUD5 contributes to HCC cell proliferation by deubiquitinating and stabilizing SLC38A1. These results may provide a theoretical basis for the development of new anti-HCC drugs.

Druglike, 18F-labeled PET Tracers Targeting Fibroblast Activation Protein.

Fibroblast activation protein (FAP) is a very reliable biomarker for tissue remodeling. FAP has so far mainly been studied in oncology, but there is growing interest in the enzyme in other diseases like fibrosis. Recently, FAP-targeting diagnostics and therapeutics have emerged, of which the so-called FAPIs are among the most promising representatives. FAPIs typically have a relatively high molecular weight and contain very polar, multicharged chelator moieties. While this is not limiting the application of FAPIs in oncology, more druglike FAPIs could be required to optimally study diseases characterized by denser, less permeable tissue. In response, we designed the first druglike 18F-labeled FAPIs. We report target potencies, biodistribution, and pharmacokinetics and demonstrate FAP-dependent uptake in murine tumor xenografts. Finally, this paper puts forward compound 10 as a highly promising, druglike FAPI for 18F-PET imaging. This molecule is fit for additional studies in fibrosis and its preclinical profile warrants clinical investigation.

A de novo dominant-negative variant is associated with OTULIN-related autoinflammatory syndrome.

OTULIN-related autoinflammatory syndrome (ORAS), a severe autoinflammatory disease, is caused by biallelic pathogenic variants of OTULIN, a linear ubiquitin-specific deubiquitinating enzyme. Loss of OTULIN attenuates linear ubiquitination by inhibiting the linear ubiquitin chain assembly complex (LUBAC). Here, we report a patient who harbors two rare heterozygous variants of OTULIN (p.P152L and p.R306Q). We demonstrated accumulation of linear ubiquitin chains upon TNF stimulation and augmented TNF-induced cell death in mesenchymal stem cells differentiated from patient-derived iPS cells, which confirms that the patient has ORAS. However, although the de novo p.R306Q variant exhibits attenuated deubiquitination activity without reducing the amount of OTULIN, the deubiquitination activity of the p.P152L variant inherited from the mother was equivalent to that of the wild-type. Patient-derived MSCs in which the p.P152L variant was replaced with wild-type also exhibited augmented TNF-induced cell death and accumulation of linear chains. The finding that ORAS can be caused by a dominant-negative p.R306Q variant of OTULIN furthers our understanding of disease pathogenesis.

Potent small molecule inhibitors against the 3C protease of foot-and-mouth disease virus.

Foot-and-mouth disease (FMD) is one of the most devastating diseases of livestock which can cause significant economic losses, especially when introduced to FMD-free countries. FMD virus (FMDV) belongs to the family Picornaviridae and is antigenically heterogeneous with seven established serotypes. The prevailing preventive and control strategies are limited to restriction of animal movement and elimination of infected or exposed animals, which can be potentially combined with vaccination. However, FMD vaccination has limitations including delayed protection and lack of cross-protection against different serotypes. Recently, antiviral drug use for FMD outbreaks has increasingly been recognized as a potential tool to augment the existing early response strategies, but limited research has been reported on potential antiviral compounds for FMDV. FMDV 3C protease (3Cpro) cleaves the viral-encoded polyprotein into mature and functional proteins during viral replication. The essential role of viral 3Cpro in viral replication and the high conservation of 3Cpro among different FMDV serotypes make it an excellent target for antiviral drug development. We have previously reported multiple series of inhibitors against picornavirus 3Cpro or 3C-like proteases (3CLpros) encoded by coronaviruses or caliciviruses. In this study, we conducted structure-activity relationship studies for our in-house focused compound library containing 3Cpro or 3CLpro inhibitors against FMDV 3Cpro using enzyme and cell-based assays. Herein, we report the discovery of aldehyde and α-ketoamide inhibitors of FMDV 3Cpro with high potency. These data inform future preclinical studies that are related to the advancement of these compounds further along the drug development pathway.IMPORTANCEFood-and-mouth disease (FMD) virus (FMDV) causes devastating disease in cloven-hoofed animals with a significant economic impact. Emergency response to FMD outbreaks to limit FMD spread is critical, and the use of antivirals may overcome the limitations of existing control measures by providing immediate protection for susceptible animals. FMDV encodes 3C protease (3Cpro), which is essential for virus replication and an attractive target for antiviral drug discovery. Here, we report a structure-activity relationship study on multiple series of protease inhibitors and identified potent inhibitors of FMDV 3Cpro. Our results suggest that these compounds have the potential for further development as FMD antivirals.

Targeting intracellular nontuberculous mycobacteria and M. tuberculosis with a bactericidal enzymatic cocktail.

To address intracellular mycobacterial infections, we developed a cocktail of four enzymes that catalytically attack three layers of the mycobacterial envelope. This cocktail is delivered to macrophages, through a targeted liposome presented here as ENTX_001. Endolytix Cocktail 1 (EC1) leverages mycobacteriophage lysin enzymes LysA and LysB, while also including α-amylase and isoamylase for degradation of the mycobacterial envelope from outside of the cell. The LysA family of proteins from mycobacteriophages has been shown to cleave the peptidoglycan layer, whereas LysB is an esterase that hydrolyzes the linkage between arabinogalactan and mycolic acids of the mycomembrane. The challenge of gaining access to the substrates of LysA and LysB provided exogenously was addressed by adding amylase enzymes that degrade the extracellular capsule shown to be present in Mycobacterium tuberculosis. This enzybiotic approach avoids antimicrobial resistance, specific receptor-mediated binding, and intracellular DNA surveillance pathways that limit many bacteriophage applications. We show this cocktail of enzymes is bactericidal in vitro against both rapid- and slow-growing nontuberculous mycobacteria (NTM) as well as M. tuberculosis strains. The EC1 cocktail shows superior killing activity when compared to previously characterized LysB alone. EC1 is also powerfully synergistic with standard-of-care antibiotics. In addition to in vitro killing of NTM, ENTX_001 demonstrates the rescue of infected macrophages from necrotic death by Mycobacteroides abscessus and Mycobacterium avium. Here, we demonstrate shredding of mycobacterial cells by EC1 into cellular debris as a mechanism of bactericide.IMPORTANCEThe world needs entirely new forms of antibiotics as resistance to chemical antibiotics is a critical problem facing society. We addressed this need by developing a targeted enzyme therapy for a broad range of species and strains within mycobacteria and highly related genera including nontuberculous mycobacteria such as Mycobacteroides abscessus, Mycobacterium avium, Mycobacterium intracellulare, as well as Mycobacterium tuberculosis. One advantage of this approach is the ability to drive our lytic enzymes through encapsulation into macrophage-targeted liposomes resulting in attack of mycobacteria in the cells that harbor them where they hide from the adaptive immune system and grow. Furthermore, this approach shreds mycobacteria independent of cell physiology as the drug targets the mycobacterial envelope while sidestepping the host range limitations observed with phage therapy and resistance to chemical antibiotics.

The antiviral response triggered by the cGAS/STING pathway is subverted by the foot-and-mouth disease virus proteases.

Propagation of viruses requires interaction with host factors in infected cells and repression of innate immune responses triggered by the host viral sensors. Cytosolic DNA sensing pathway of cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING) is a major component of the antiviral response to DNA viruses, also known to play a relevant role in response to infection by RNA viruses, including foot-and-mouth disease virus (FMDV). Here, we provide supporting evidence of cGAS degradation in swine cells during FMDV infection and show that the two virally encoded proteases, Leader (Lpro) and 3Cpro, target cGAS for cleavage to dampen the cGAS/STING-dependent antiviral response. The specific target sequence sites on swine cGAS were identified as Q140/T141 for the FMDV 3Cpro and the KVKNNLKRQ motif at residues 322-330 for Lpro. Treatment of swine cells with inhibitors of the cGAS/STING pathway or depletion of cGAS promoted viral infection, while overexpression of a mutant cGAS defective for cGAMP synthesis, unlike wild type cGAS, failed to reduce FMDV replication. Our findings reveal a new mechanism of RNA viral antagonism of the cGAS-STING innate immune sensing pathway, based on the redundant degradation of cGAS through the concomitant proteolytic activities of two proteases encoded by an RNA virus, further proving the key role of cGAS in restricting FMDV infection.

In vitro functional analysis and in silico structural modelling of pathogen-secreted polyglycine hydrolases.

Polyglycine hydrolases are fungal effectors composed of an N-domain with unique sequence and structure and a C-domain that resembles ß-lactamases, with serine protease activity. These secreted fungal proteins cleave Gly-Gly bonds within a polyglycine sequence in corn ChitA chitinase. The polyglycine hydrolase N-domain (PND) function is unknown. In this manuscript we provide evidence that the PND does not directly participate in ChitA cleavage. In vitro analysis of site-directed mutants in conserved residues of the PND of polyglycine hydrolase Es-cmp did not specifically impair protease activity. Furthermore, in silico structural models of three ChitA-bound polyglycine hydrolases created by High Ambiguity Driven protein-protein DOCKing (HADDOCK) did not predict significant interactions between the PND and ChitA. Together these results suggest that the PND has another function. To determine what types of PND-containing proteins exist in nature we performed a computational analysis of Foldseek-identified PND-containing proteins. The analysis showed that proteins with PNDs are present throughout biology as either single domain proteins or fused to accessory domains that are diverse but are usually proteases or kinases.

Reduced peptidoglycan synthesis capacity impairs growth of E. coli at high salt concentration.

Gram-negative bacteria have a thin peptidoglycan layer between the cytoplasmic and outer membranes protecting the cell from osmotic challenges. Hydrolases of this structure are needed to cleave bonds to allow the newly synthesized peptidoglycan strands to be inserted by synthases. These enzymes need to be tightly regulated and their activities coordinated to prevent cell lysis. To better understand this process in Escherichia coli, we probed the genetic interactions of mrcA (encodes PBP1A) and mrcB (encodes PBP1B) with genes encoding peptidoglycan amidases and endopeptidases in envelope stress conditions. Our extensive genetic interaction network analysis revealed relatively few combinations of hydrolase gene deletions with reduced fitness in the absence of PBP1A or PBP1B, showing that none of the amidases or endopeptidases is strictly required for the functioning of one of the class A PBPs. This illustrates the robustness of the peptidoglycan growth mechanism. However, we discovered that the fitness of ∆mrcB cells is significantly reduced under high salt stress and in vitro activity assays suggest that this phenotype is caused by a reduced peptidoglycan synthesis activity of PBP1A at high salt concentration.IMPORTANCEEscherichia coli and many other bacteria have a surprisingly high number of peptidoglycan hydrolases. These enzymes function in concert with synthases to facilitate the expansion of the peptidoglycan sacculus under a range of growth and stress conditions. The synthases PBP1A and PBP1B both contribute to peptidoglycan expansion during cell division and growth. Our genetic interaction analysis revealed that these two penicillin-binding proteins (PBPs) do not need specific amidases, endopeptidases, or lytic transglycosylases for function. We show that PBP1A and PBP1B do not work equally well when cells encounter high salt stress and demonstrate that PBP1A alone cannot provide sufficient PG synthesis activity under this condition. These results show how the two class A PBPs and peptidoglycan hydrolases govern cell envelope integrity in E. coli in response to environmental challenges and particularly highlight the importance of PBP1B in maintaining cell fitness under high salt conditions.

P. aeruginosa CtpA protease adopts a novel activation mechanism to initiate the proteolytic process.

During bacterial cell growth, hydrolases cleave peptide cross-links between strands of the peptidoglycan sacculus to allow new strand insertion. The Pseudomonas aeruginosa carboxyl-terminal processing protease (CTP) CtpA regulates some of these hydrolases by degrading them. CtpA assembles as an inactive hexamer composed of a trimer-of-dimers, but its lipoprotein binding partner LbcA activates CtpA by an unknown mechanism. Here, we report the cryo-EM structures of the CtpA-LbcA complex. LbcA has an N-terminal adaptor domain that binds to CtpA, and a C-terminal superhelical tetratricopeptide repeat domain. One LbcA molecule attaches to each of the three vertices of a CtpA hexamer. LbcA triggers relocation of the CtpA PDZ domain, remodeling of the substrate binding pocket, and realignment of the catalytic residues. Surprisingly, only one CtpA molecule in a CtpA dimer is activated upon LbcA binding. Also, a long loop from one CtpA dimer inserts into a neighboring dimer to facilitate the proteolytic activity. This work has revealed an activation mechanism for a bacterial CTP that is strikingly different from other CTPs that have been characterized structurally.

The discovery of potent USP2/USP8 dual-target inhibitors for the treatment of breast cancer via structure guided optimization of ML364.

USP2 and USP8 are crucial in the development and progression of breast cancer, primarily through the stabilization of protein substrates such as Her2 and ERα. The dual-target inhibitor ML364, targeting both USP2 and USP8, has garnered significant interest in recent research. In this study, we developed a series of ML364 derivatives using ligand-based drug design strategies. The standout compound, LLK203, demonstrated enhanced inhibitory activity, showing a 4-fold increase against USP2 and a 9-fold increase against USP8, compared to the parent molecule. In MCF-7 breast cancer cells, LLK203 effectively degraded key proteins involved in cancer progression and notably inhibited cell proliferation. Moreover, LLK203 exhibited potent in vivo efficacy in the 4T1 homograft model, while maintaining a low toxicity profile. These results underscore the potential of LLK203 as a promising dual-target inhibitor of USP2/USP8 for breast cancer treatment.