Transglutaminase as a blood clotting enzyme

Transglutaminase 1 and 2 are localized in different blood cells in the freshwater crayfish Pacifastacus leniusculus

In the present study we show that hemocytes in the freshwater crayfish Pacifastacus leniusculus express two different transglutaminases. We describe the sequence of a previously unknown TGase (Pl_TGase1) and named this as Pl_TGase2 and compared this sequence with similar sequences from other crustaceans. The catalytic core domain is similar to the previously described TGase in P. leniusculus, but Pl_TGase2 has significant differences in the N-terminal and C-terminal domains. Further, we show conclusive evidences that these different transglutaminases are specific for different hemocyte types so that Pl_TGase1 is expressed in the hematopoietic tissue and in the cytoplasm of semigranular hemocytes, while Pl_TGase2 is expressed in vesicles in the granular hemocytes. By in situ hybridization we show that both Pl_TGase1 and Pl_TGase2 mRNA are present only in a subset of the respective hemocyte population. This observation indicates that there may be different subtypes of semigranular as well as granular hemocytes which may have different specific functions.

Enzyme-catalysed polymer cross-linking: Biocatalytic tools for chemical biology, materials science and beyond

Intermolecular cross-linking is one of the most important techniques that can be used to fundamentally alter the material properties of a polymer. The introduction of covalent bonds between individual polymer chains creates 3D macromolecular assemblies with enhanced mechanical properties and greater chemical or thermal tolerances. In contrast to many chemical cross-linking reactions, which are the basis of thermoset plastics, enzyme catalysed processes offer a complimentary paradigm for the assembly of cross-linked polymer networks through their predictability and high levels of control. Additionally, enzyme catalysed reactions offer an inherently 'greener' and more biocompatible approach to covalent bond formation, which could include the use of aqueous solvents, ambient temperatures, and heavy metal-free reagents. Here, we review recent progress in the development of biocatalytic methods for polymer cross-linking, with a specific focus on the most promising candidate enzyme classes and their underlying catalytic mechanisms. We also provide exemplars of the use of enzyme catalysed cross-linking reactions in industrially relevant applications, noting the limitations of these approaches and outlining strategies to mitigate reported deficiencies.

Inhibition of transglutaminase exacerbates polyglutamine-induced neurotoxicity by increasing the aggregation of mutant ataxin-3 in an SCA3 Drosophila model

Transglutaminases (TGs) comprise a family of Ca(2+)-dependent enzymes that catalyze protein cross-linking, which include nine family members in humans but only a single homolog in Drosophila with three conserved domains. Drosophila Tg plays important roles in cuticle morphogenesis, hemolymph clotting, and innate immunity. Mammalian tissue TG (TG2) is involved in polyglutamine diseases (polyQ diseases), and TG6 has been identified as a causative gene of a novel spinocerebellar ataxia, SCA35. Using a well-established SCA3 fly model, we found that RNA interference-mediated suppression of Tg aggravated polyQ-induced neurodegenerative phenotypes. The administration of cystamine, a known effective Tg inhibitor, enhanced ommatidial degeneration in SCA3 flies. We also demonstrated that the aggregates of pathogenic ataxin-3 increased greatly, when the Tg activity was repressed. These findings indicate that Tg is crucial for polyQ-induced neurotoxicity because Tg ablation resulted in more severe neurodegeneration due to the elevated accumulation of insoluble ataxin-3 complexes in the SCA3 Drosophila model.

Role of protein transamidation in serotonin-induced proliferation and migration of pulmonary artery smooth muscle cells

Pulmonary hypertension is characterized by elevated pulmonary artery pressure and pulmonary artery smooth muscle cell (SMC) proliferation and migration. Clinical and experimental evidence suggests that serotonin (5-HT) is important in these responses. We previously demonstrated the participation of the 5-HT transporter and intracellular 5-HT (5-HTi) in the pulmonary vascular SMC-proliferative response to 5-HT. However, the mechanism underlying the intracellular actions of 5-HT is unknown. We speculated that 5-HTi activates SMC growth by post-translational transamidation of proteins via transglutaminase (TGase) activity, a process referred to as serotonylation. To test this hypothesis, serotonylation of pulmonary artery SMC proteins, and their role in 5-HT-induced proliferative and migratory responses, were assessed. 5-HT caused dose- and time-dependent increase in serotonylation of multiple proteins in both bovine and rat pulmonary artery SMCs. Inhibition of TGase with dansylcadaverin blocked this activity, as well as SMC-proliferative and migratory responses to 5-HT. Serotonylation of proteins also was blocked by 5-HT transporter inhibitors, and was enhanced by inhibition of monoamine oxidase, an enzyme known to degrade 5-HTi, indicating that 5-HTi levels regulate serotonylation. Immunoprecipitation assays and HPLC-mass spectral peptide sequencing revealed that a major protein serotonylated by TGase was fibronectin (FN). 5-HT-stimulated SMC serotonylation and proliferation were blocked by FN small interfering (si) RNA. These findings, together with previous observations that FN expression in the lung strongly correlates with the progression of pulmonary hypertension in both experimental animals and humans, suggest an important role of FN serotonylation in the pathogenesis of this disease.

Barnacle cement: a polymerization model based on evolutionary concepts

Enzymes and biochemical mechanisms essential to survival are under extreme selective pressure and are highly conserved through evolutionary time. We applied this evolutionary concept to barnacle cement polymerization, a process critical to barnacle fitness that involves aggregation and cross-linking of proteins. The biochemical mechanisms of cement polymerization remain largely unknown. We hypothesized that this process is biochemically similar to blood clotting, a critical physiological response that is also based on aggregation and cross-linking of proteins. Like key elements of vertebrate and invertebrate blood clotting, barnacle cement polymerization was shown to involve proteolytic activation of enzymes and structural precursors, transglutaminase cross-linking and assembly of fibrous proteins. Proteolytic activation of structural proteins maximizes the potential for bonding interactions with other proteins and with the surface. Transglutaminase cross-linking reinforces cement integrity. Remarkably, epitopes and sequences homologous to bovine trypsin and human transglutaminase were identified in barnacle cement with tandem mass spectrometry and/or western blotting. Akin to blood clotting, the peptides generated during proteolytic activation functioned as signal molecules, linking a molecular level event (protein aggregation) to a behavioral response (barnacle larval settlement). Our results draw attention to a highly conserved protein polymerization mechanism and shed light on a long-standing biochemical puzzle. We suggest that barnacle cement polymerization is a specialized form of wound healing. The polymerization mechanism common between barnacle cement and blood may be a theme for many marine animal glues.

The end product of transglutaminase crosslinking: simultaneous quantitation of [Nepsilon-(gamma-glutamyl) lysine] and lysine by HPLC-MS3

Transglutaminases catalyze the formation of Nepsilon-(gamma-glutamyl) isodipeptide crosslinks between proteins. These enzymes are thought to participate in a number of diseases, including neurological disease and cancer. A method associating liquid chromatography and multiple stage mass spectrometry has been developed for the simultaneous quantitation of [Nepsilon-(gamma-glutamyl) lysine] isodipeptide and lysine on an ion trap mass spectrometer. Highly specific detection has been achieved in MS3 mode. The method includes a derivatization step consisting of butylation of carboxylic groups and acetylation of amide groups, a liquid-liquid extraction, and a 19-min separation on a 100x2.1-mm Beta-basic C18 column with an acetonitrile gradient elution. 13C6-(15)N2 isotopes of the isodipeptide and the lysine serve as internal standards. The assay was linear in the range of 50 pmol/ml to 75 nmol/ml for the isodipeptide and the range of 10 nmol/ml to 3.5 micromol/ml for the lysine, with correlation coefficients greater than 0.99 for both ions. Intra- and inter-day coefficients of variation ranged from 3.5 to 15.9%. The method was successfully applied to human biological samples known to be crosslinked by transglutaminase such as cornified envelopes of epidermis, fibrin, and normal and Huntington disease brain.

[Nepsilon-(gamma-glutamyl) lysine] as a potential biomarker in neurological diseases: new detection method and fragmentation pathways

Protein aggregates are characteristic of a number of diseases of the central nervous system such as diseases of polyQ expansion. Covalent bonds formed by the action of transglutaminase are thought to participate in the stabilization of these aggregates. Transglutaminase catalyzes the formation of cross-links between the side chains of glutaminyl and lysyl residues of polypeptides. Identification of the isodipeptide N(epsilon)-(gamma-glutamyl) lysine (iEK) in terminal proteolytic digests of neuronal aggregates would demonstrate participation of transglutaminase in neurological diseases. In order to identify and quantify the iEK present in the brain of patients with neurological disease, a method combining liquid chromatography and multistep mass spectrometry was developed. Because isobaric peptides of iEK could be present in the digest of aggregated proteins, the choice of fragment diagnostic ions was crucial. These ions were identified by mass spectrometry on sodiated iEK, which was derivatized on the carboxylic functions and terminal amines in order to improve sensitivity. Deuterated molecules as well as (13)C(6)- and (15)N(2)-isotopomers were used to derive filiations in the multistep fragmentations. The main fragmentation patterns have been identified, so that two ions (m/z 396 [MH - 56-42 u](+) and 350 [MH - 56-88 u](+)) are shown to be adequate markers for quantitation experiments. In order to gain a better understanding of the fragmentation processes, detailed quantum chemical calculations have been performed at levels which are expected to provide good accuracy. A thorough study has been carried out with a reduced model in which only the 'active' part of the molecule is retained. This allowed obtaining full mechanistic details on the pathways leading to a number of observed fragments. In particular, it has been shown that losses of 87 and 88 u from A(+) = [MH - 56 u](+) are competitive. Computations on the entire derivatized isodipeptide have been used to validate the use of the smaller model in order to obtain reliable energetics and mechanisms.

Transglutaminases: crosslinking enzymes with pleiotropic functions

Blood coagulation, skin-barrier formation, hardening of the fertilization envelope, extracellular-matrix assembly and other important biological processes are dependent on the rapid generation of covalent crosslinks between proteins. These reactions--which are catalysed by transglutaminases--endow the resulting supramolecular structure with extra rigidity and resistance against proteolytic degradation. Some transglutaminases function as molecular switches in cytoskeletal scaffolding and modulate protein-protein interactions. Having knowledge of these enzymes is essential for understanding the aetiologies of diverse hereditary diseases of the blood and skin, and various autoimmune, inflammatory and degenerative conditions.

Factor XIII: structure, activation, and interactions with fibrinogen and fibrin

Fibrin stabilizing factor (factor XIII or FXIII) plays a critical role in the generation of a viable hemostatic plug. Following exposure to thrombin and calcium, the zymogen is activated to FXIIIa that, in turn, catalyzes the formation of N epsilon(gamma-glutamyl)lysine protein-to-protein side chain bridges within the clot network. Introduction of these covalent crosslinks greatly augments the viscoelastic storage modulus of the structure and its resistance to fibrinolytic enzymes. Analysis of the individual reaction steps and regulatory control mechanisms involved in clot stabilization enabled us to reconstruct the entire physiological process. This also serves as a guide for the differential diagnosis of the variety of molecular defects of fibrin stabilization.

Hydrolysis of gamma:epsilon isopeptides by cytosolic transglutaminases and by coagulation factor XIIIa

Nepsilon-(gamma-glutamyl)lysine cross-links, connecting various peptide chain segments, are frequently the major products in transglutaminase-catalyzed reactions. We have now investigated the effectiveness of these enzymes for hydrolyzing the gamma:epsilon linkage. Branched compounds were synthesized, in which the backbone on the gamma-side of the cross-bridge was labeled with a fluorophor (5-(dimethylamino)-1-naphthalenesulfonyl or 2-aminobenzoyl) attached through an epsilon-aminocaproyl linker in the N-terminal position, and the other branch of the bridge was constructed with Lys methylamide or diaminopentane blocked by 2,4-dinitrophenyl at the Nalpha position. Hydrolysis of the cross-link could be followed in these internally quenched substrates by an increase in fluorescence. In addition to the thrombin and Ca2+-activated human coagulation Factor XIIIa, cytosolic transglutaminases from human red cells and from guinea pig liver were tested. All three enzymes were found to display good isopeptidase activities, with Km values of 10(-4) to 10(-5) M. Inhibitors of transamidation were effective in blocking the hydrolysis by the enzymes, indicating that expression of isopeptidase activity did not require unusual protein conformations. We suggest that transglutaminases may play a dynamic role in biology not only by promoting the formation but also the breaking of Nepsilon-(gamma-glutamyl)lysine isopeptides.

Characterization of a clotting protein, isolated from plasma of the freshwater crayfish Pacifastacus leniusculus

A protein responsible for clot formation was isolated from plasma of the crayfish Pacifastacus leniusculus, by repeated precipitation at low ionic strength, pH 6.0. The protein, here named clotting protein (CP), is a lipoglycoprotein, which consists of two 210-kDa subunits, covalently associated by disulfide bonds. Preparations of the CP can form stable clots in the presence of crayfish haemocyte lysate supernatant, which contains endogenous, Ca(2+)-dependent transglutaminase (TGase) activity. The covalent, TGase-mediated polymerization of CP could clearly be visualized in SDS/PAGE under reducing conditions, where the 210-kDa subunit is covalently cross-linked into dimeric, trimeric and higher polymeric forms. The CP was shown to be a substrate for transglutaminases, since two different fluorescent TGase substrates, namely dansylcadaverine and a dansylated glutamine-containing peptide, were incorporated into the CP subunit by active TGase. This indicates the presence of both glutamine and lysine residues in the CP, accessible for TGase cross-linking. The amino acid composition and the N-terminal amino acid sequence of the clotting protein was determined.

Cloning and expression of chicken erythrocyte transglutaminase

We report the sequences of cDNAs encoding chicken erythrocyte transglutaminase (EC 2.3.2.13). The complete mRNA consists of 3345/3349 nucleotides and predicts a single open reading frame. Nine peptide sequences derived from partial digests of the isolated protein agreed with the corresponding translation of the open reading frame. Approximately 60% identities between the avian protein and three related mammalian enzymes were found. Chicken erythrocyte transglutaminase mRNA is most abundant in red blood cells and kidney, and it accumulates during erythroid cell differentiation.

Cross-linked A alpha.gamma chain hybrids serve as unique markers for fibrinogen polymerized by tissue transglutaminase

Notwithstanding the high degree of amino acid sequence homologies between human factor XIIIa on the one hand and intracellular transglutaminases (protein-glutamine:amine gamma-glutamyltransferase, EC 2.3.2.13) from guinea pig liver or human erythrocytes on the other, we find that the two sets of enzymes differ remarkably in the mode of cross-linking the same protein substrate--i.e., human fibrinogen. In the program of polymerization with factor XIIIa, production of the known gamma-gamma' homologous chain pairs is the dominant feature, whereas with either intracellular transglutaminase, a series of hitherto unidentified A alpha.gamma hybrid chain combinations, designated A alpha p gamma q (p and q = 1, 2, 3...), is generated and practically no gamma-gamma' dimers are formed. Two-dimensional electrophoresis is particularly useful for demonstrating the production of A alpha p gamma q structures by protein staining as well as by immunoblotting against specific antibodies to the A alpha and gamma chains of fibrinogen. These findings should aid in deciding whether the direct cross-linking of fibrinogen by transglutaminase might contribute to thrombotic processes in addition to the thrombin- and factor XIIIa-dependent pathway of clot formation.

Native fibrin gel networks and factors influencing their formation in health and disease

Hydrated fibrin gels were studied by confocal laser 3D microscopy, liquid permeation and turbidity. The gels from normal fibrinogen were found to be composed of straight rod-like fiber elements which sometimes originated from denser nodes. In gels formed at increasing thrombin or fibrinogen concentrations, the gel networks became tighter and the porosity decreased. The fiber strands also became shorter. Gel porosity of the network decreased dramatically in gels formed at increasing ionic strengths. Shortening of the fibers were observed and fiber swelling occurred at ionic strength above 0.24. Albumin and dextran, when present in the gel forming system, affected the formation of more porous structures with strands of larger mass-length ratio and fiber thickness. This type of gels were also formed in plasma. Albumin and lipoproteins may be among the determinants for the formation of this type of gel structure in plasma. Gels formed when factor XIIIa instead of thrombin was used as catalyst for gelation showed a completely different structure in which lumps of polymeric material were held together by a network of fine fiber strands. Our studies have also shown that the methodologies employed may be useful in studies of gel structures in certain dysfibrinogenemias as well as in other diseases. We give examples of two patients with abnormal fibrinogen and of patients with ischaemic heart disease.

Fibrinogen Aarhus and factor XIII induced polymerization and gel formation

Fibrinogen Aarhus is an abnormal fibrinogen for which the clotting time with thrombin is greatly prolonged both in plasma and in the isolated fibrinogen. The whole blood clotting time is only slightly prolonged. The patient with this fibrinogen has no bleeding tendency. In this report we have investigated fibrinogen Aarhus in two alternative, thrombin independent polymerization and gelation pathways. These pathways are the factor XIII dependent oligomerization and gelation of fibrinogen, and heteropolymer (fibrinogen-fibronectin) formation which also is catalysed by factor XIII. Both of these reactions are qualitatively the same in fibrinogen Aarhus as in normal fibrinogen, but the rate of oligomerization is somewhat slower in fibrinogen Aarhus. This may depend on impaired association between factor XIII and fibrinogen Aarhus.

FXIII induced gelation of human fibrinogen--an alternative thiol enhanced, thrombin independent pathway

Factor XIII induced gelation of human fibrinogen in the presence of calcium ions. At the end of this reaction between 95 and 100% of the fibrinogen was incorporated into the gel matrix. The gelation was dramatically enhanced by DTT. Cysteine and beta-mercaptoethanol also enhanced the reaction, but less efficiently. Thrombin activated factor XIII led to shortened gelation time and increased the rate of gelation. The reaction was inhibited by p-chloromercuribenzoate and iodoacetamide. Neither fibrinopeptide A, nor fibrinopeptide B were released during gelation, while quantitative release of FPA by thrombin was demonstrated from preformed gel matrices. SDS-PAGE showed the presence of gamma-dimers and alpha-polymers in the gel matrix. In the clot supernatants gamma-dimers were observed already before the gel point. We also observed that the clotting of fibrinogen by thrombin was perturbed by DTT. Preincubation of fibrinogen with calcium ions prevented this effect of DTT.

Diagnostic and genetic studies on fibrin-stabilizing factor with a new assay based on amine incorporation

Fibrinoligase, the fibrin cross-linking enzyme, transiently appearing during the course of coagulation in normal blood, was shown to catalyze the incorporation of a fluorescent amine, monodansylcadaverine [or N-(5-aminopentyl)-5-dimethylamino-1-naphthalene-sulfonamide] into casein. The reaction provided the basis of a sensitive fluorimetric method for measuring the activity of the enzyme (and also of similar other transpeptidases, such as transglutaminase). In tests involving plasma, certain difficulties had to be overcome which were mainly due to the fact that the enzyme itself does not occur in citrated plasma. Only its precursor (fibrin-stabilizing factor or factor XIII) is present, still requiring limited proteolytic activation by thrombin. Thus, in order to measure amine incorporation with plasma as a source of the factor, thrombin must be added. This necessitated a differential desensitization of the intrinsic fibrinogen so that the latter could not clot and could not thereby interfere with amine incorporation. Also, the thrombin-inactivating capacity of plasma had to be saturated to enable full conversion of the factor to the transpeptidase. Concentrations of casein, monodansylcadaverine, calcium, and hydrogen ions were chosen to permit almost maximal velocity of amine incorporation. A linear relationship with regard to plasma concentration could be obtained only under such conditions. No similar assay is presently available for quantitatively evaluating fibrin-stabilizing factor levels in plasma.The amine incorporation test was applied to a clinical case of hereditary total fibrin-stabilizing factor deficiency. The effect of transfusion therapy was studied, and some of the patient's relatives were examined. Whereas a paternal aunt and uncle gave values well within the normal range, a brother and the mother proved to be partially deficient and could be considered as heterozygous carriers. The father appeared to have a reduced level of fibrin-stabilizing factor, though not quite as low as the other two relatives. Two infusions (1 liter each) of fresh normal plasma, administered about 26 hr apart, brought levels in the patient's plasma close to those found in the mother and brother. The corrective power of the transfusions, however, rapidly declined within 5-6 days. Futility of the last transfusion could be ascribed to the appearance of a neutralizing antibody directed against the precursor stabilizing factor, a serious complication. General diagnostic versatility and potential of the quantitative amine incorporation assay with plasma is discussed.

[Cross-link in fibrin polymerized by factor 13: epsilon-(gamma-glutamyl)lysine]

(epsilon)-((gamma)-Glutamyl)lysine has been isolated from enzymatic hydrolyzates of cross-linked human fibrin. This compound was not detected in "non-cross-linked" fibrin prepared with ethylenediaminetetraacetic acid, which inhibits factor XIII; intermediate amounts were observed when the fibrin was prepared with glycine ethyl ester, which inhibits factor XIII competitively. These and ancillary experiments furnish conclusive evidence that epsilon-(gamma-glutamyl)lysine cross-links form in human fibrin during polymerization catalyzed by factor XIII.

A pathological inhibitor of fibrin cross-linking

Lewis et al. recently reported on a patient who died of hemorrhages attributable to an acquired inhibitor of fibrin-stabilizing factor. They indicated that the inhibitor was associated with the immune globulins. Using the postmortem serum in the isolated fibrin cross-linking system, we have now further localized the site of inhibition in the scheme of blood coagulation. The interference occurs at the transpeptidation step catalyzed by the thrombin-activated fibrin-stabilizing factor. The patient's serum also uniquely delayed the clotting time of Homarus plasma, a test for specific inhibitors of transpeptidation. Since the inhibitor was effective in two such widely different systems, it probably is not an antibody, but falls into the category of cross-linking inhibitors which we have previously described (4, 5, 10, 12-17). While the exact nature of the inhibitor remains unknown, we raise the question whether some unusual metabolic transformation of isonicotinic acid hydrazide (with which the patient was treated and which itself we found to be a potent inhibitor fibrin cross-linking), in combination with a macromolecule, might not have given rise to an inhibitory compound.