The Evolution of Transglutaminases Underlies the Origin and Loss of Cornified Skin Appendages in Vertebrates

Transglutaminases (TGMs) cross-link proteins by introducing covalent bonds between glutamine and lysine residues. These cross-links are essential for epithelial cornification which enables tetrapods to live on land. Here, we investigated which evolutionary adaptations of vertebrates were associated with specific changes in the family of TGM genes. We determined the catalog of TGMs in the main clades of vertebrates, performed a comprehensive phylogenetic analysis of TGMs, and localized the distribution of selected TGMs in tissues. Our data suggest that TGM1 is the phylogenetically oldest epithelial TGM, with orthologs being expressed in the cornified teeth of the lamprey, a basal vertebrate. Gene duplications led to the origin of TGM10 in stem vertebrates, the origin of TGM2 in jawed vertebrates, and an increasing number of epithelium-associated TGM genes in the lineage leading to terrestrial vertebrates. TGM9 is expressed in the epithelial egg tooth, and its evolutionary origin in stem amniotes coincided with the evolution of embryonic development in eggs that are surrounded by a protective shell. Conversely, viviparous mammals have lost both the epithelial egg tooth and TGM9. TGM3 and TGM6 evolved as regulators of cornification in hair follicles and underwent pseudogenization upon the evolutionary loss of hair in cetaceans. Taken together, this study reveals the gain and loss of vertebrate TGM genes in association with the evolution of cornified skin appendages and suggests an important role of TGM9 in the evolution of amniotes.

The Role of Transglutaminase 2 in Cancer: An Update

Transglutaminase type 2 (TG2) is the most ubiquitously expressed and well characterized member of the transglutaminase family. It is a ubiquitous multifunctional enzyme implicated in the regulation of several cellular pathways that support the survival, death, and general homeostasis of eukaryotic cells. Due to its multiple localizations both inside and outside the cell, TG2 participates in the regulation of many crucial intracellular signaling cascades in a tissue- and cell-specific manner, making this enzyme an important player in disease development and progression. Moreover, TG2 is capable of modulating the tumor microenvironment, a process of dynamic tissue remodeling and biomechanical events, resulting in changes which influence tumor initiation, growth, and metastasis. Even if generally related to the Ca2+-dependent post-translational modification of proteins, a number of different biological functions have been ascribed to TG2, like those of a peptide isomerase, protein kinase, guanine nucleotide binder, and cytosolic-nuclear translocator. With respect to cancer, TG2's role is controversial and highly debated; it has been described both as an anti- and pro-apoptotic factor and is linked to all the processes of tumorigenesis. However, numerous pieces of evidence support a tissue-specific role of TG2 so that it can assume both oncogenic and tumor-suppressive roles.

Mesenchymal Transglutaminase 2 Activates Epithelial ADAM17: Link to G-Protein-Coupled Receptor 56 (ADGRG1) Signalling

A wound healing model was developed to elucidate the role of mesenchymal-matrix-associated transglutaminase 2 (TG2) in keratinocyte re-epithelialisation. TG2 drives keratinocyte migratory responses by activation of disintegrin and metalloproteinase 17 (ADAM17). We demonstrate that epidermal growth factor (EGF) receptor ligand shedding leads to EGFR-transactivation and subsequent rapid keratinocyte migration on TG2-positive ECM. In contrast, keratinocyte migration was impaired in TG2 null conditions. We show that keratinocytes express the adhesion G-protein-coupled receptor, ADGRG1 (GPR56), which has been proposed as a TG2 receptor. Using ADAM17 activation as a readout and luciferase reporter assays, we demonstrate that TG2 activates GPR56. GPR56 activation by TG2 reached the same level as observed with an agonistic N-GPR56 antibody. The N-terminal GPR56 domain is required for TG2-regulated signalling response, as the constitutively active C-GPR56 receptor was not activated by TG2. Signalling required the C-terminal TG2 β-barrel domains and involved RhoA-associated protein kinase (ROCK) and ADAM17 activation, which was blocked by specific inhibitors. Cell surface binding of TG2 to the N-terminal GPR56 domain is rapid and is associated with TG2 and GPR56 endocytosis. TG2 and GPR56 represent a ligand receptor pair causing RhoA and EGFR transactivation. Furthermore, we determined a binding constant for the interaction of human TG2 with N-GPR56 and show for the first time that only the calcium-enabled "open" TG2 conformation associates with N-GPR56.

Urinary Protein-Biomarkers Reliably Indicate Very Early Kidney Damage in Children With Alport Syndrome Independently of Albuminuria and Inflammation

Introduction

Alport syndrome (AS) is a hereditary type IV collagen disease. It starts shortly after birth, without clinical symptoms, and progresses to end-stage kidney disease early in life. The earlier therapy starts, the more effectively end-stage kidney disease can be delayed. Clearly then, to ensure preemptive therapy, early diagnosis is an essential prerequisite.

Methods

To provide early diagnosis, we searched for protein biomarkers (BMs) by mass spectrometry in dogs with AS stage 0. At this very early stage, we identified 74 candidate BMs. Of these, using commercial enzyme-linked immunosorbent assays (ELISAs), we evaluated 27 in dogs and 28 in children, 50 with AS and 104 healthy controls.

Results

Most BMs from blood appeared as fractions of multiple variants of the same protein, as shown by their chromatographic distribution before mass spectrometry. Blood samples showed only minor differences because ELISAs rarely detect disease-specific variants. However, in urine , several proteins, individually or in combination, were promising indicators of very early and preclinical kidney injury. The BMs with the highest sensitivity and specificity were collagen type XIII, hyaluronan binding protein 2 (HABP2), and complement C4 binding protein (C4BP).

Conclusion

We generated very strong candidate BMs by our approach of first examining preclinical AS in dogs and then validating these BMs in children at early stages of disease. These BMs might serve for screening purposes for AS before the onset of kidney damage and therefore allow preemptive therapy.

Prevalence of Coagulopathy in Patients with Celiac Disease: A Single-Center Retrospective Case-Control Study

Introduction: Despite being one of the most frequent chronic digestive diseases worldwide, with a prevalence of 1%, celiac disease (CD) remains severely underdiagnosed. Among the instruments used to improve its diagnostic rate, hematologic parameters have been proposed as screening tests to select patients with an increased probability of having CD. Assessment of coagulation is included in routine check-ups, and CD has been reported to be associated with coagulopathy. We aimed to assess if subtle changes in coagulation tests could be used in clinical practice to prompt testing for CD. Methods: We retrospectively recruited all patients with clinical suspicion for CD during a study period of 7 years (between 2015 and 2022), who were tested using IgA tissue transglutaminase (tTG) serology and serum total IgA (IgG tTG in case of IgA deficiency) and who underwent upper gastrointestinal endoscopy with multiple biopsy sampling of the duodenal bulb and distal duodenum. We stratified patients into three groups: newly diagnosed CD, gluten-free diet-treated CD, and non-CD controls. Results: Altogether, there were 133 CD patients (71 newly diagnosed, 62 GFD-treated) and 57 non-CD controls. Mean age and gender distribution were similar among the three groups: 43.3 years for newly diagnosed CD, 41.6 years for non-CD controls, and 44 years for GFD-treated CD patients, with a male gender distribution of 21.1%, 28%, and 24.1%, respectively. Among the included newly diagnosed CD patients, 14% had a prolonged INR. The mean INR was slightly higher in newly diagnosed CD patients, compared to GFD-treated CD patients and non-CD controls: 1.12 ± 0.30, 1.02 ± 0.83, and 1.00 ± 0.08, respectively (p = 0.009). Consequently, prothrombin activity was slightly lower in newly diagnosed CD patients, compared to GFD-treated CD and non-CD controls: 94.9 ± 19.3%, 102.3 ± 12.8%, and 101.9 ± 15.15, respectively. Interestingly, after GFD, the mean INR and prothrombin activity of CD individuals reached a value similar to that of non-CD controls. Conclusions: Subtle changes in INR, defined as a value within the normal range, but closer to the upper limit, could be an indicator of probability for CD.

Multicenter study to compare the diagnostic performance of CLIA vs. FEIA transglutaminase IgA assays for the diagnosis of celiac disease

OBJECTIVES

Celiac disease (CD) is an immune-mediated enteropathy driven by gluten intake. Presence of tTG-IgA antibodies is important for the diagnosis. However, different tTG-IgA assays are used and test performance may vary. Therefore, a retrospective multicenter study was performed to compare the diagnostic performance of three assays.

METHODS

The fluorescence enzyme-linked immunoassay (FEIA) EliA Celikey IgA (Phadia), the chemiluminescence immunoassays (CLIA) h-tTG IgA QUANTA Flash® (Inova Diagnostics) and the anti-tTG ChLIA IgA (Euroimmun) were compared. Diagnostic samples from CD cases (95 adults; 65 children) and controls (479 adults; 253 children) were included. Samples were blinded and reanalyzed on all platforms.

RESULTS

A high quantitative correlation between platforms was found (p<0.0001). Both CLIA were more sensitive (adults 100%; children 100%) compared to the FEIA (adults 88.4%; children 96.6%). Specificity of all assays was high (≥97.6%) with the FEIA having the highest specificity. A cut-off based on receiver operator characteristic analysis (6.5 U/mL) improved the sensitivity of the FEIA (adults 95.8%; children 100%) without affecting specificity. Cut-off values for the CLIA assays did not need further optimization. With the FEIA, 71% of pediatric cases had a tTG-IgA level ≥10× upper limit of normal compared to 91 and 92% with QUANTA Flash and ChLIA, respectively.

CONCLUSIONS

All platforms have high diagnostic accuracy. The CLIA assays are more sensitive compared to the FEIA assay. A lower cut-off for the FEIA improves diagnostic performance, particularly in adult cases that, as demonstrated in this study, present with lower tTG-IgA levels compared to pediatric cases.

Chlorpyrifos Oxon Activates Glutamate and Lysine for Protein Cross-linking

Chronic low-dose exposure to organophosphorus (OP) toxicants is correlated with an increase in the risk of impaired cognition and neurodegenerative diseases. A mechanism to explain this relationship is needed. We suggest that the formation of organophosphate-induced high-molecular-weight protein aggregates that disrupt cell function may be the missing link. It has been demonstrated that such aggregation can be promoted by OP-labeled lysine. Alternatively, OP-labeled glutamate may be the initiator. To test this hypothesis, we treated MAP-rich tubulin Sus scrofa and human transglutaminase with chlorpyrifos oxon. Trypsin-digested proteins were subjected to liquid chromatography-tandem mass spectrometry followed by Protein Prospector searches to identify diethyl phosphate adducts and cross-linked peptides. We report the presence of diethyl phosphate adducts on the side chains of glutamate, lysine, and tyrosine, as well as cross-links between glutamate and lysine. Glutamate-lysine cross-linking could be initiated either by diethyl phosphate-activated glutamate or by diethyl phosphate-activated lysine to form stable isopeptide bonds between and within proteins. It was concluded that organophosphate-induced high-molecular-weight protein aggregates could promote brain dysfunction.

Novel association of gluten sensitivity with immune-mediated neuromuscular syndrome in a dog

Gluten-related disorders in humans comprise different entities, including coeliac disease. Patients typically have measurable titers of anti-gliadin IgG or IgA (AGAs) and anti-transglutaminase-2 IgA (TG2). In addition to intestinal symptoms, human patients often show various neurological complications. In dogs, the neurological manifestation is rarely reported. Here we describe the muscle and nerve biopsies of an 11-year-old, male Border Terrier presenting with lower motor neuron signs submitted for histological examination. Examination of the biopsies showed an oligofocal lymphohistiocytic and plasmocytic myositis and a diffuse neuropathy of mixed nodo-paranodal and demyelinating type. Suspecting a neuromuscular form of breed-related gluten hypersensitivity, measurements of AGAs and TG2 antibodies were performed. Both titers ranged above control values. Hence, a gluten-related neuromyopathy was diagnosed. A gluten-free diet was prescribed and a complete disappearance of clinical signs was observed. Gluten-related disorders should be considered as a differential diagnosis in dogs with intestinal and neuromuscular signs.

Naturally Occurring Epsilon Gamma Glutamyl Lysine Isopeptide Crosslinks in Human Neuroblastoma SH-SY5Y Cells

Zero-length isopeptide crosslinks between the side chains of glutamine and lysine are the product of transglutaminase activity. It is generally accepted that transglutaminase activity is dormant under physiological conditions because the calcium concentration inside cells is too low to activate transglutaminase to an open conformation with access to the catalytic triad. Traditional assays for transglutaminase activity measure incorporation of biotin pentylamine or of radiolabeled putrescine in the presence of added calcium. In this report, we identified naturally occurring isopeptide crosslinked proteins using the following steps: immunopurification of tryptic peptides by binding to anti-isopeptide antibody 81D1C2, separation of immunopurified peptides by liquid chromatography-tandem mass spectrometry, Protein Prospector database searches of mass spectrometry data for isopeptide crosslinked peptides, and manual evaluation of candidate crosslinked peptide pairs. The most labor intense step was manual evaluation. We developed criteria for accepting and rejecting candidate crosslinked peptides and showed examples of MS/MS spectra that confirm or invalidate a possible crosslink. The SH-SY5Y cells that we examined for crosslinked proteins had not been exposed to calcium and had been lysed in the presence of ethylenediaminetetraacetic acid. This precaution allows us to claim that the crosslinks we found inside the cells occurred naturally under physiological conditions. The quantity of crosslinks was very low, and the crosslinked proteins were mostly low abundance proteins. In conclusion, intracellular transglutaminase crosslinking/transamidase activity is very low but detectable. The low level of intracellular crosslinked proteins is consistent with tight regulation of transglutaminase activity.

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.

Plant Transglutaminases: New Insights in Biochemistry, Genetics, and Physiology

Transglutaminases (TGases) are calcium-dependent enzymes that catalyse an acyl-transfer reaction between primary amino groups and protein-bound Gln residues. They are widely distributed in nature, being found in vertebrates, invertebrates, microorganisms, and plants. TGases and their functionality have been less studied in plants than humans and animals. TGases are distributed in all plant organs, such as leaves, tubers, roots, flowers, buds, pollen, and various cell compartments, including chloroplasts, the cytoplasm, and the cell wall. Recent molecular, physiological, and biochemical evidence pointing to the role of TGases in plant biology and the mechanisms in which they are involved allows us to consider their role in processes such as photosynthesis, plant fertilisation, responses to biotic and abiotic stresses, and leaf senescence. In the present paper, an in-depth description of the biochemical characteristics and a bioinformatics comparison of plant TGases is provided. We also present the phylogenetic relationship, gene structure, and sequence alignment of TGase proteins in various plant species, not described elsewhere. Currently, our knowledge of these proteins in plants is still insufficient. Further research with the aim of identifying and describing the regulatory components of these enzymes and the processes regulated by them is needed.

A gene-centric approach to biomarker discovery identifies transglutaminase 1 as an epidermal autoantigen

The nine-member transglutaminase protein family includes five known autoantigens. Because of the frequent roles of transglutaminases in autoimmunity, we decided to explore whether the remaining members might also constitute autoantigens, but in as-yet-unexplained disorders. We turned to TGM1, and since this member is primarily expressed in squamous epithelia, we focused on skin disorders. By screening a broad range of acquired skin disorders, we identified TGM1 to be a major autoantigen in the severe blistering disease paraneoplastic pemphigus. This study illustrates a gene-centric approach to biomarker discovery—starting from a putative autoantigen to search for its corresponding disease—that may prove generally applicable for studies of autoimmunity.

Autoantigen discovery is a critical challenge for the understanding and diagnosis of autoimmune diseases. While autoantibody markers in current clinical use have been identified through studies focused on individual disorders, we postulated that a reverse approach starting with a putative autoantigen to explore multiple disorders might hold promise. We here targeted the epidermal protein transglutaminase 1 (TGM1) as a member of a protein family prone to autoimmune attack. By screening sera from patients with various acquired skin disorders, we identified seropositive subjects with the blistering mucocutaneous disease paraneoplastic pemphigus. Validation in further subjects confirmed TGM1 autoantibodies as a 55% sensitive and 100% specific marker for paraneoplastic pemphigus. This gene-centric approach leverages the wealth of data available for human genes and may prove generally applicable for biomarker discovery in autoimmune diseases.

Mechanotransduction in fibrosis: Mechanisms and treatment targets

To perceive and integrate the environmental cues, cells and tissues sense and interpret various physical forces like shear, tensile, and compression stress. Mechanotransduction involves the sensing and translation of mechanical forces into biochemical and mechanical signals to guide cell fate and achieve tissue homeostasis. Disruption of this mechanical homeostasis by tissue injury elicits multiple cellular responses leading to pathological matrix deposition and tissue stiffening, and consequent evolution toward pro-inflammatory/pro-fibrotic phenotypes, leading to tissue/organ fibrosis. This review focuses on the molecular mechanisms linking mechanotransduction to fibrosis and uncovers the potential therapeutic targets to halt or resolve fibrosis.

Evaluation of a Bi-Analyte Immunoblot as a Useful Tool for Diagnosing Dermatitis Herpetiformis

Immune responses to tissue transglutaminase (tTG) and nonapeptides of gliadin (npG) are associated with dermatitis herpetiformis (DH), a gluten-related dermatosis. Recently, a bi-analyte immunoblot (b-aIB) was introduced to detect IgA antibodies in response to tTG and npG. We compared the utility of ELISA and b-aIB with tTG in serological diagnoses of DH and their agreement with direct immunofluorescence (DIF). In total, 55 sera (27 DIF-positive DH patients, 4 DIF-negative DH patients and 24 healthy controls) were examined. ELISA for anti-tTG IgA, b-aIB for anti-npG and anti-tTG IgA, and statistical analysis were performed. The b-aIB with tTG showed 78% sensitivity, 100% specificity, 100% positive predictive value, and 82% negative predictive value in relation to ELISA. A better rate of agreement (Cohen’s kappa values) in IgA detection was observed in the pair tTG ELISA and b-aIB with npG (0.85) than in pairs tTG ELISA and b-aIB with tTG (0.78) or b-aIB with tTG and b-aIB with npG (0.78). No degree of agreement was found between serological tests and DIF. Both serological tests may be used to detect the anti-tTG IgA in DH patients. Still, DH diagnosing requires careful consideration of clinical data as well as results of tissue imaging (crucial DIF) and immunoserological techniques detecting DH-type features.

Evaluation of mass spectrometry MS/MS spectra for the presence of isopeptide crosslinked peptides

Isopeptide crosslinked proteins can be the product of transglutaminase or of exposure to organophosphorus toxicants (OP). Transglutaminase links glutamine to lysine with loss of ammonia. OP toxicants induce a link between glutamic acid and lysine with loss of water. Our goal was to establish criteria to distinguish real from false isopeptide crosslinks reported by software searches of mass spectrometry data. We used fragmentation spectra of tryptic peptides from MAP-rich tubulin Sus scrofa as a test system for detection of naturally-occurring isopeptide crosslinks. Data were analyzed with Protein Prospector. Criteria for the assignments included the presence of at least 1 crosslink specific product ion, fragment ions from both peptides, Protein Prospector scores ≥20, and best fit of the MS/MS data to the crosslinked peptide as opposed to a linear peptide. Out of 301,364 spectra, 15 potential transglutaminase-type crosslinked peptide candidates were identified. Manual evaluation of these MS/MS spectra reduced the number to 1 valid crosslink between Q112 of NFH and K368 of Tau. Immunopurification with anti-isopeptide 81D1C2 confirmed that MAP-rich tubulin contained only one isopeptide. Support for this isopeptide bond was obtained by showing that transglutaminase was capable of incorporating dansyl-aminohexyl -QQIV into K368. A model of the KIETHK-QLEAHNR isopeptide was synthesized with the aid of transglutaminase. MS/MS spectra of the model validated our interpretation of the native isopeptide. An OP-induced isopeptide bond between K163 of tubulin alpha-1A and E158 of tubulin beta-4B was induced by treating MAP-rich tubulin with 100 μM chlorpyrifos oxon. This crosslink was supported by the criteria described above and by the presence of diethoxyphospho-lysine 163 in the tubulin alpha-1A peptide. The information obtained in this work is valuable for future studies that aim to understand why exposure to OP is associated with increased risk of neurodegenerative disease.

Zinc as a modulator of transglutaminase activity - Laboratory and pathophysiological aspects

For a whole century, citrate has been used as an in vitro anticoagulant via chelation of calcium. Later, also EDTA was introduced as an anticoagulant. An often overlooked fact is that zinc is bound to citrate and EDTA with affinities much greater than that for calcium, imposing problems in biomedical research. In vivo, proteins of the S100 family are released from leukocytes and known to bind calcium. Some of them, e.g., calprotectin, also chelate zinc. Thus, at an inflamed site, the ratio between Ca²⁺ and Zn²⁺ is changed. This mechanism is of importance for the modulation of the activation of a fascinating family of post-translationally acting calcium-dependent thiol enzymes, the transglutaminases, which are inhibited by zinc. This presentation illustrates the complexity of in vitro studies with zinc. Moreover, it exemplifies the role of Zn²⁺ in pathophysiological situations such as celiac disease and neurodegeneration.

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Citrate, EDTA and DTT bind zinc as well as calcium.

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At inflammation, calprotectin binds Zn²⁺, which leads to low concentrations of the ion.

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Zn²⁺ inhibits the activation of transglutaminases and peptidylarginine deiminases.

The physiology, pathology and potential therapeutic application of serotonylation

The classical neurotransmitter serotonin or 5-hydroxytryptamine (5-HT), synthesized from tryptophan, can be produced both centrally and peripherally. Through binding to functionally distinct receptors, serotonin is profoundly implicated in a number of fundamental physiological processes and pathogenic conditions. Recently, serotonin has been found covalently incorporated into proteins, a newly identified post-translational modification termed serotonylation. Transglutaminases (TGMs), especially TGM2, are responsible for catalyzing the transamidation reaction by transferring serotonin to the glutamine residues of target proteins. Small GTPases, extracellular matrix protein fibronectin, cytoskeletal proteins and histones are the most reported substrates for serotonylation, and their functions are triggered by this post-translational modification. This Review highlights the roles of serotonylation in physiology and diseases and provides perspectives for pharmacological interventions to ameliorate serotonylation for disease treatment.

Gene disruption of medaka (Oryzias latipes) orthologue for mammalian tissue-type transglutaminase (TG2) causes movement retardation

Transglutaminases are an enzyme family that catalyses protein cross-linking essential for several biological functions. In the previous studies, we characterized the orthologues of the mammalian transglutaminase family in medaka (Oryzias latipes), an established fish model. Among the human isozymes, tissue-type transglutaminase (TG2) has multiple functions that are involved in several biological phenomena. In this study, we established medaka mutants deficient for the orthologue of human TG2 using the CRISPR/Cas9 and transcription activator-like effector nucleases systems. Although apparent morphological changes in the phenotype were not observed, movement retardation was found in the mutant fish when evaluated by a tank-diving test. Furthermore, comparative immunohistochemistry analysis using in this fish model revealed that orthologue of human TG2 was expressed at the periventricular layer of the optic tectum. Our findings provide novel insight for the relationship between tissue-type transglutaminase and the nervous system and the associated behaviour.

Mechanism of semen liquefaction and its potential for a novel non-hormonal contraception†

Semen liquefaction is a proteolytic process where a gel-like ejaculated semen becomes watery due to the enzymatic activity of prostate-derived serine proteases in the female reproductive tract. The liquefaction process is crucial for the sperm to gain their motility and successful transport to the fertilization site in Fallopian tubes (or oviducts in animals). Hyperviscous semen or failure in liquefaction is one of the causes of male infertility. Therefore, the biochemical inhibition of serine proteases in the female reproductive tract after ejaculation is a prime target for novel contraceptive development. Herein, we will discuss protein components in the ejaculates responsible for semen liquefaction and any developments of contraceptive methods in the past that involve the liquefaction process.

Signature Ions in MS/MS Spectra for Dansyl-Aminohexyl-QQIV Adducts on Lysine

Bacterial transglutaminase was used to label human plasma proteins with fluorescent tags. Protein lysines were modified with dansyl-epsilon-aminohexyl-Gln-Gln-Ile-Val-OH (dansylQQIV), while protein glutamines were modified with dansyl cadaverine. Labeled proteins included human butyrylcholinesterase, apolipoprotein A-1, haptoglobin, haptoglobin-related protein, immunoglobulin heavy chain, and hemopexin. Tryptic peptides were analyzed by LC-MS/MS on an Orbitrap Fusion Lumos mass spectrometer. Modified residues were identified in Protein Prospector and Proteome Discoverer searches of mass spectrometry data. The MS/MS fragmentation spectra from dansylQQIV-modified peptides gave intense peaks at 475.2015, 364.1691, 347.1426, 234.0585, and 170.0965 m/z. These signature ions are useful markers for identifying modified peptides. Human butyrylcholinesterase retained full activity following modification by dansylQQIV or dansyl cadaverine.

Interplay between Type 2 Transglutaminase (TG2), Gliadin Peptide 31-43 and Anti-TG2 Antibodies in Celiac Disease

Celiac disease (CD) is a common intestinal inflammatory disease involving both a genetic background and environmental triggers. The ingestion of gluten, a proteic component of several cereals, represents the main hexogen factor implied in CD onset that involves concomitant innate and adaptive immune responses to gluten. Immunogenicity of some gluten sequences are strongly enhanced as the consequence of the deamidation of specific glutamine residues by type 2 transglutaminase (TG2), a ubiquitous enzyme whose expression is up-regulated in the intestine of CD patients. A short gluten sequence resistant to intestinal proteases, the α-gliadin peptide 31-43, seems to modulate TG2 function in the gut; on the other hand, the enzyme can affect the biological activity of this peptide. In addition, an intense auto-immune response towards TG2 is a hallmark of CD. Auto-antibodies exert a range of biological effects on several cells, effects that in part overlap with those induced by peptide 31-43. In this review, we delineate a scenario in which TG2, anti-TG2 antibodies and peptide 31-43 closely relate to each other, thus synergistically participating in CD starting and progression.

Epilepsy, cerebral calcifications, and gluten-related disorders: Are anti-transglutaminase 6 antibodies the missing link?

PURPOSE

Gluten-related disorders (GRDs) are a group of immune-mediated diseases often associated to neurologic manifestations. Epilepsies with cerebral calcifications, with or without coeliac disease (CD), are rare neurological disorders characterized by childhood-onset focal seizures, often refractory to antiepileptic drugs. Transglutaminase 6 antibodies (anti-TG6) have been considered a biomarker for gluten-related ataxia and neuropathy, but their prevalence in epilepsies with cerebral calcifications is unknown. The aim of this study is to evaluate anti-TG6 prevalence in patients with epilepsies and cerebral calcifications.

METHOD

this was a cross-sectional study conducted at five Italian epilepsy centres. The following groups were included. Group 1: nine patients with CD, posterior cerebral calcifications and epilepsy (CEC); group 2: nine patients with epilepsy and posterior cerebral calcifications, without CD; group 3: twenty patients with focal epilepsy of unknown etiology; group 4: twenty-two healthy controls (HC). All subjects were tested for serological evidence of anti-TG6 IgA and IgG. Differences among groups were analysed using χ ² test.

RESULTS

anti-TG6 were present in 1/9 subjects (11%) of group 1, 2/9 subjects (22%) of group 2, 0/20 subjects in group 3, 3/22 (13.6%) of HC. No significant difference was found among the 4 groups.

CONCLUSIONS

Anti-TG6 do not seem to be associated to epilepsies with cerebral calcifications.