An Unusual "OR" Gate for Allosteric Regulation of Mammalian Transglutaminase 2 in the Extracellular Matrix

The adaptive regulation mechanism of Anammox granule sludge under calcium ions stress: Defense modes transformation

Anammox granular sludge (AnGS) has received considerable attention due to its low carbon footprint (less aeration energy and carbon source consumption) and high biomass density, but growth rate and stability are still the bottlenecks of AnGS process. Calcium ion (Ca2+) is essential for the growth of anaerobic ammonium oxidation bacteria (AnAOB) and plays an important role in the formation and stability of AnGS. Response of AnGS to Ca2+ under different concentrations was comprehensively investigated by multi-spectral and metagenomics analysis in four aspects: nitrogen removal performance, surface morphology, extracellular polymeric substance (EPS) composition and characterization, and microbial community. The nitrogen removal efficiency was significantly enhanced at appropriate Ca2+ concentration (2 mmol/L), owning to the more favorable morphology and functional microbial composition of AnGS. However, the nitrogen removal performance of AnGS declined with the Ca2+concentration increased from 2 to 8 mmol/L, due to the negative effects of excess Ca2+on EPS, mass transfer efficiency, and functional microorganisms. Meanwhile, an unexpected slight "rebound" of nitrogen removal efficiency was observed at Ca2+ = 6 mmol/L and attributed to the defense mode transformation of AnGS (from "ion stabilization" to "precipitate shield" modes) against excess Ca2+ stress. Based on the findings, the response mechanism of AnGS to Ca2+ with different concentrations was established. Our results enhanced the understanding of the interaction between AnGS and Ca2+, which may be valuable for filling the theoretical gap in enhancing the granulation and stability of AnGS and providing a reference for the practical operation of the AnGS process.

Structural and mechanistic analysis of Ca2+-dependent regulation of transglutaminase 2 activity using a Ca2+-bound intermediate state

Mammalian transglutaminases, a family of Ca2+-dependent proteins, are implicated in a variety of diseases. For example, celiac disease (CeD) is an autoimmune disorder whose pathogenesis requires transglutaminase 2 (TG2) to deamidate select glutamine residues in diet-derived gluten peptides. Deamidation involves the formation of transient γ-glutamyl thioester intermediates. Recent studies have revealed that in addition to the deamidated gluten peptides themselves, their corresponding thioester intermediates are also pathogenically relevant. A mechanistic understanding of this relevance is hindered by the absence of any structure of Ca2+-bound TG2. We report the X-ray crystallographic structure of human TG2 bound to an inhibitory gluten peptidomimetic and two Ca2+ ions in sites previously designated as S1 and S3. Together with additional structure-guided experiments, this structure provides a mechanistic explanation for how S1 regulates formation of an inhibitory disulfide bond in TG2, while also establishing that S3 is essential for γ-glutamyl thioester formation. Furthermore, our crystallographic findings and associated analyses have revealed that i) two interacting residues, H305 and E363, play a critical role in resolving the thioester intermediate into an isopeptide bond (transamidation) but not in thioester hydrolysis (deamidation); and ii) residues N333 and K176 stabilize preferred TG2 substrates and inhibitors via hydrogen bonding to nonreactive backbone atoms. Overall, the intermediate-state conformer of TG2 reported here represents a superior model to previously characterized conformers for both transition states of the TG2-catalyzed reaction.

LRP-1 links post-translational modifications to efficient presentation of celiac disease-specific T cell antigens

Celiac disease (CeD) is an autoimmune disorder in which gluten-derived antigens trigger inflammation. Antigenic peptides must undergo site-specific deamidation to be presentable to CD4+ T cells in an HLA-DQ2 or -DQ8 restricted manner. While the biochemical basis for this post-translational modification is understood, its localization in the patient's intestine remains unknown. Here, we describe a mechanism by which gluten peptides undergo deamidation and concentration in the lysosomes of antigen-presenting cells, explaining how the concentration of gluten peptides necessary to elicit an inflammatory response in CeD patients is achieved. A ternary complex forms between a gluten peptide, transglutaminase-2 (TG2), and ubiquitous plasma protein α2-macroglobulin, and is endocytosed by LRP-1. The covalent TG2-peptide adduct undergoes endolysosomal decoupling, yielding the expected deamidated epitope. Our findings invoke a pathogenic role for dendritic cells and/or macrophages in CeD and implicate TG2 in the lysosomal clearance of unwanted self and foreign extracellular proteins.

Features of ZED1227: The First-In-Class Tissue Transglutaminase Inhibitor Undergoing Clinical Evaluation for the Treatment of Celiac Disease

ZED1227 is a small molecule tissue transglutaminase (TG2) inhibitor. The compound selectively binds to the active state of TG2, forming a stable covalent bond with the cysteine in its catalytic center. The molecule was designed for the treatment of celiac disease. Celiac disease is an autoimmune-mediated chronic inflammatory condition of the small intestine affecting about 1–2% of people in Caucasian populations. The autoimmune disease is triggered by dietary gluten. Consumption of staple foods containing wheat, barley, or rye leads to destruction of the small intestinal mucosa in genetically susceptible individuals, and this is accompanied by the generation of characteristic TG2 autoantibodies. TG2 plays a causative role in the pathogenesis of celiac disease. Upon activation by Ca²⁺, it catalyzes the deamidation of gliadin peptides as well as the crosslinking of gliadin peptides to TG2 itself. These modified biological structures trigger breaking of oral tolerance to gluten, self-tolerance to TG2, and the activation of cytotoxic immune cells in the gut mucosa. Recently, in an exploratory proof-of-concept study, ZED1227 administration clinically validated TG2 as a “druggable” target in celiac disease. Here, we describe the specific features and profiling data of the drug candidate ZED1227. Further, we give an outlook on TG2 inhibition as a therapeutic approach in indications beyond celiac disease.

Toehold-Mediated Cascade Catalytic Assembly for Mycotoxin Detection and Its Logic Applications

In this work, an enzyme-free biosensor is reported for mycotoxin detection based on a toehold-mediated catalytic hairpin assembly (CHA) and a DNAzyme-cascaded hydrolysis reaction. In the presence of a mycotoxin, the recognition between an aptamer and the mycotoxin releases the trigger DNA. The trigger DNA initiates the toehold-mediated CHA, generating large amounts of partial duplex B/C with four toeholds, which can be used to assemble the DNAzyme-cascaded hydrolysis reaction. Furthermore, through a collaborative autoassembly reaction among the B/C duplex, DNA1, and DNA2, supramolecular nanostructures corresponding to Mg²⁺-dependent DNAzymes can be formed. With the incubation of Mg²⁺, the dual-modified (TAMRA/BHQ2) substrate strand DNA2 will be cleaved into two fragments, yielding a high TAMRA fluorescence signal for mycotoxin testing. Under optimal conditions, the sensing system was ultrasensitive and showed low detection limits of 0.2 pM for ochratoxin A (OTA), 0.13 pM for aflatoxin B1 (AFB1), and 0.17 pM for zearalenone (ZEN). The mycotoxin aptasensor also exhibited high selectivity and was successfully applied for the quantitative analysis of OTA, AFB1, and ZEN in wine samples. Due to the advantages of flexibility and versatility, this mycotoxin platform was used to fabricate several concatenated logic gates including "AND-INHIBIT", "INHIBIT-OR", "OR-AND", and "OR-INHIBIT" logic biocomputings. Such multiple functions of the logic system provided a universal sensing strategy for the intelligent detection of multiplex mycotoxins, demonstrating considerable potential in food safety and environmental monitoring.