Transglutaminase-mediated transamidation of serotonin, dopamine and noradrenaline to fibronectin: Evidence for a general mechanism of monoaminylation

The activity of some small GTPases is regulated by covalent transamidation of serotonin (5-hydropxytryptamien) to glutamine residues of the enzymes. This process is mediated by transglutaminase (TGase) and is termed “serotonylation”. In addition, serotonylation of neural proteins and proteins of the extracellular matrix such as fibronectin has been demonstrated. Here we show that the catecholamines dopamine (DA) and noradrenaline (NA) inhibit serotonylation of fibronectin and that DA and NA themselves can be selectively transamidated into fibronectin by TGase. All three biogenic monoamines also block TGase-mediated transamidation of another monoamine, monodansylacadaverine, into fibronectin, suggesting a general mechanism of TGase-mediated “monoaminylation”.     

Targeted Overexpression of Drosophila Transglutaminase-B Induced Characteristic Phenotypes in a Manner Similar to Transglutaminase-A

The Drosophila transglutaminase gene (CG7356) encodes two transglutaminases, dTG-A and dTG-B. To understand the roles of dTG-B during the development of the fly, we examined phenotypes induced through ectopic expression of dTG-B. Overexpression of dTG-B induced rough eye and extra wing crossvein phenotypes. These phenotypes were similar to those observed in the case of targeted overexpression of dTG-A.     

Improvement of Shark Type I Collagen with Microbial Transglutaminase in Urea

In the presence of urea, type I collagen could form a gel with crosslinks with microbial transglutaminase (MTGase). Collagen self-assembly was accelerated with the addition of MTGase. The proportion of reconstructed collagen fibrils was raised with the addition of MTGase. MTGase-treated collagen gel remained gelled at high temperatures at which collagen denatured. By treatment with MTGase, collagen could form the gel under impossible condition to collagen self-assembly, and that denaturation temperature was raised.     

Characterization of Human Recombinant Transglutaminase 1 Purified from Baculovirus-infected Insect Cells

Transglutaminase 1 (TGase 1) is required for the formation of a cornified envelope in stratified squamous epithelia. Recombinant human TGase 1 expressed in baculovirus-infected cells was purified in a soluble form at the molecular mass of 92 kDa. Recombinant TGase 1 was susceptible to limited proteolysis by both μ- and m-calpains, the calcium-dependent intracellular cysteine proteases. Although the proteolysis did not induce the elevation of the specific enzyme activity of TGase 1, the requirement of calcium ion in the enzymatic reaction was reduced. Furthermore, the effects of GTP, nitric oxide, and sphingosylphosphocholine, known as regulatory factors for tissue-type isozyme (TGase 2), on the enzymatic activity of TGase 1 were investigated.     

Epitope mapping of the N‐terminal portion of tissue transglutaminase protein antigen to identify linear epitopes in celiac disease

Celiac disease (CD) is an autoimmune mediated disease with complex and multifactorial etiology. Gluten intake triggers a composite immune response involving T‐cells and B‐cells and leading to the secretion of autoantibodies if a genetic predisposition is present. Untreated CD patients show high levels of circulating autoantibodies directed to different auto‐antigens present in the intestinal mucosa. The most important auto‐antigen is the endomysial enzyme tissue transglutaminase (tTG). Both IgA and IgG antibody isotypes to tTG are known, but only the IgA antibodies demonstrate the highest disease specificity and thus are considered disease biomarkers. Because the pathogenicity and exact tTG binding properties of these autoantibodies are still unclear, the characterization of tTG antigenic domains is a crucial step in understanding CD onset and the autoimmune pathogenesis. Overlapping peptide libraries can be used for epitope mapping of selected protein portions to determine antigenic fragments contributing to the immunological activity and possibly develop innovative peptide‐based tools with high specificity and sensitivity for CD. We performed an epitope mapping study to characterize putative linear auto‐antigenic epitopes present in the tTG N‐terminal portion (1–230). A library of 23 overlapping peptides spanning tTG(1–230) was generated by Fmoc/tBu solid‐phase peptide synthesis and screened by immunoenzymatic assays employing patients' sera. The results indicate that four synthetic peptides, that is, Ac‐tTG(1–15)‐NH₂, Ac‐tTG(41–55)‐NH₂, Ac‐tTG(51–65)‐NH₂, and Ac‐tTG(151–165)‐NH₂, are recognized by IgA autoantibodies circulating in CD patients' sera. These results offer important insight on the nature of the antigen‐antibody interaction. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

Remodeling of tobacco thylakoids by over-expression of maize plastidial transglutaminase

Transglutaminases (TGases, EC 2.3.2.13) are intra- and extra-cellular enzymes that catalyze post-translational modification of proteins by establishing ?-(γ-glutamyl) links and covalent conjugation of polyamines. In chloroplast it is well established that TGases specifically polyaminylate the light-harvesting antenna of Photosystem (PS) II (LHCII, CP29, CP26, CP24) and therefore a role in photosynthesis has been hypothesised (Della Mea et al. [23] and refs therein). However, the role of TGases in chloroplast is not yet fully understood. Here we report the effect of the over-expression of maize (Zea mays) chloroplast TGase in tobacco (Nicotiana tabacum var. Petit Havana) chloroplasts. The transglutaminase activity in over-expressers was increased 4 times in comparison to the wild-type tobacco plants, which in turn increased the thylakoid associated polyamines about 90%. Functional comparison between Wt tobacco and tgz over-expressers is shown in terms of fast fluorescence induction kinetics, non-photochemical quenching of the singlet excited state of chlorophyll a and antenna heterogeneity of PSII. Both in vivo probing and electron microscopy studies verified thylakoid remodeling. PSII antenna heterogeneity in vivo changes in the over-expressers to a great extent, with an increase of the centers located in grana-appressed regions (PSIIα) at the expense of centers located mainly in stroma thylakoids (PSIIβ). A major increase in the granum size (i.e. increase of the number of stacked layers) with a concomitant decrease of stroma thylakoids is reported for the TGase over-expressers.     

Leishmania species: evidence for transglutaminase activity and its role in parasite proliferation

Albeit transglutaminase (TGase) activity has been reported to play crucial physiological roles in several organisms including parasites; however, there was no previous report(s) whether Leishmania parasites exhibit this activity. We demonstrate herein that TGase is functionally active in Leishmania parasites by using labeled polyamine that becomes conjugated into protein substrates. The parasite enzyme was about 2- to 4-fold more abundant in Old World species than in New World ones. In L. amazonensis, comparable TGase activity was found in both promastigotes and amastigotes. TGase activity in either parasite stage was optimal at the basic pH, but the enzyme in amastigote lysates was more stable at higher temperatures (37-55 degrees C) than that in promastigote lysates. Leishmania TGase differs from mouse macrophage (M Phi) TGase in two ways: (1) the parasite enzyme is Ca(2+)-independent, whereas the mammalian TGase depends on the cation for activity, and (2) major protein substrates for L. amazonensis TGase were found within the 50-75 kDa region, while those for the M Phi TGase were located within 37-50 kDa. The potential contribution of TGase-catalyzed reactions in promastigote proliferation was supported by findings that standard inhibitors of TGase [e.g., monodansylcadaverine (MDC), cystamine (CS), and iodoacetamide (IodoA)], but not didansylcadaverine (DDC), a close analogue of MDC, had a profound dose-dependent inhibition on parasite growth. Myo-inositol-1-phosphate synthase and leishmanolysin (gp63) were identified as possible endogenous substrates for L. amazonensis TGase, implying a role for TGase in parasite growth, development, and survival.     

LTBP-1 blockade in dioxin receptor-null mouse embryo fibroblasts decreases TGF-beta activity: Role of extracellular proteases plasmin and elastase

In mouse embryonic fibroblasts (MEF) lacking dioxin receptor (AhR), high levels of latent transforming growth factor-beta (TGF-beta)-binding protein-1 (LTBP-1) correlated with increased TGF-beta1 activity, an observation suggesting that LTBP-1 could contribute to maintain TGF-beta1 levels. Here, using small interfering RNAs (siRNA), we have first analyzed if LTBP-1 expression affected TGF-beta1 activity in MEF cells. We have then determined how LTBP-1 levels could alter the activity of extracellular proteases known to activate TGF-beta1, and finally, whether protease inhibition could reduce TGF-beta1 activation. LTBP-1 inhibition by siRNA in AhR-/- MEF decreased the amount of active TGF-beta1 and reduced plasminogen activators (PA)/plasmin and elastase activities and thrombospondin-1 (TSP-1) expression, without significantly affecting their mRNA levels. On the contrary, LTBP-1 siRNA restored matrix metalloproteinase-2 (MMP-2) activity in AhR-/- MEF. Interestingly, whereas a TGF-beta1 neutralizing antibody mimicked many of the LTBP-1 siRNA effects on extracellular proteases, addition of recombinant TGF-beta1 protein increased proteases activity over basal levels in AhR-/- MEF. These proteases contributed to TGF-beta activation since their specific inhibitors reduced active TGF-beta levels in these cells. These results suggest that LTBP-1 contributes to TGF-beta1 activation in MEF, possibly by influencing the activities of PA/plasmin, elastase, TSP-1, and MMP-2. TGF-beta1, on the other hand, could be also involved in maintaining the activity of these extracellular proteases. Thus, LTBP-1 appears to play a role in TGF-beta1 activation through a process involving extracellular protease activities, which, in turn, could be affected by TGF-beta1 levels.     

Site-specific labeling of proteins for single-molecule FRET by combining chemical and enzymatic modification

An often limiting factor for studying protein folding by single-molecule fluorescence resonance energy transfer (FRET) is the ability to site-specifically introduce a photostable organic FRET donor (D) and a complementary acceptor (A) into a polypeptide chain. Using alternating-laser excitation and chymotrypsin inhibitor 2 as a model, we show that chemical labeling of a unique cysteine, followed by enzymatic modification of a reactive glutamine in an N-terminally appended substrate sequence recognition tag for transglutaminase (TGase) affords stoichiometrically D-/A-labeled protein suitable for single-molecule FRET experiments. Thermodynamic data indicate that neither the presence of the TGase tag nor D/A labeling perturbs protein stability. As the N terminus in proteins is typically solvent accessible, a TGase tag can (in principle) be appended to any protein of interest by genetic engineering. Two-step chemical/enzymatic labeling may thus represent a simple, low-cost, and widely available strategy for D/A labeling of proteins for FRET-based single-molecule protein folding studies, even for non-protein-experts laboratories.     

Degradation of transglutaminase 2 by calcium-mediated ubiquitination responding to high oxidative stress

Transglutaminase 2 (TG2) is a calcium-dependent enzyme that catalyzes the transamidation reaction. There is conflicting evidence on the role of TG2 in apoptosis. In this report, we show that TG2 increases in response to low level of oxidative stress, whereas TG2 diminishes under high stress conditions. Monitoring TG2 expression, activity and calcium concentration in cells treated with A23187 revealed that the initial rise of calcium activates TG2 but subsequent calcium-overload induces the degradation of TG2 via calcium-mediated polyubiquitination. These results indicate that the role of TG2 in apoptosis depends on the level of calcium influx triggered by oxidative stress.

Structured summary

MINT-6824687: TG2 (uniprotkb:P21980) physically interacts (MI:0218) with Ubiquitin (uniprotkb:P62988) by anti bait coimmunoprecipitation (MI:0006)