Reversible activation of cellular factor XIII by calcium

Review: Application of chitosan and its derivatives in medical materials

Chitin is a natural polymeric polysaccharide extracted from marine crustaceans, and chitosan is obtained by removing part of the acetyl group (usually more than 60 %) in chitin's structure. Chitosan has attracted wide attention from researchers worldwide due to its good biodegradability, biocompatibility, hypoallergenic and biological activities (antibacterial, immune and antitumor activities). However, research has shown that chitosan does not melt or dissolve in water, alkaline solutions and general organic solvents, which greatly limits its application range. Therefore, researchers have carried out extensive and in-depth chemical modification of chitosan and prepared a variety of chitosan derivatives, which have expanded the application field of chitosan. Among them, the most extensive research has been conducted in the pharmaceutical field. This paper summarizes the application of chitosan and chitosan derivatives in medical materials over the past five years.

Peptidic Inhibitors and a Fluorescent Probe for the Selective Inhibition and Labelling of Factor XIIIa Transglutaminase

Factor XIIIa (FXIIIa) is a transglutaminase of major therapeutic interest for the development of anticoagulants due to its essential role in the blood coagulation cascade. While numerous FXIIIa inhibitors have been reported, they failed to reach clinical evaluation due to their lack of metabolic stability and low selectivity over transglutaminase 2 (TG2). Furthermore, the chemical tools available for the study of FXIIIa activity and localization are extremely limited. To combat these shortcomings, we designed, synthesised, and evaluated a library of 21 novel FXIIIa inhibitors. Electrophilic warheads, linker lengths, and hydrophobic units were varied on small molecule and peptidic scaffolds to optimize isozyme selectivity and potency. A previously reported FXIIIa inhibitor was then adapted for the design of a probe bearing a rhodamine B moiety, producing the innovative KM93 as the first known fluorescent probe designed to selectively label active FXIIIa with high efficiency (k_inact/K_I = 127,300 M^-1 min^-1) and 6.5-fold selectivity over TG2. The probe KM93 facilitated fluorescent microscopy studies within bone marrow macrophages, labelling FXIIIa with high efficiency and selectivity in cell culture. The structure-activity trends with these novel inhibitors and probes will help in the future study of the activity, inhibition, and localization of FXIIIa.

Genetic landscape in coagulation factor XIII associated defects – Advances in coagulation and beyond

Coagulation factor XIII (FXIII) acts as a fine fulcrum in blood plasma that maintains the balance between bleeding and thrombosis by covalently crosslinking the pre-formed fibrin clot into an insoluble one that is resistant to premature fibrinolysis. In plasma, FXIII circulates as a pro-transglutaminase complex composed of the dimeric catalytic FXIII-A encoded by the F13A1 gene and dimeric carrier/regulatory FXIII-B subunits encoded by the F13B gene. Growing evidence accumulated over decades of exhaustive research shows that not only does FXIII play major roles in both pathological extremes of hemostasis i.e. bleeding and thrombosis, but that it is, in fact, a pleiotropic protein with physiological roles beyond coagulation. However, the current FXIII genetic-epidemiological literature is overwhelmingly derived from the bleeding pathology associated with its deficiency. In this article we review the current clinical, functional, and molecular understanding of this fascinating multifaceted protein, especially putting into the same perspective its genetic landscape.

Vasoconstrictor and coagulation activator entrapped chitosan based composite hydrogel for rapid bleeding control

Chitosan (Cs) as a hemostatic agent has been in use to control hemorrage. Composite hydrogel formed by entrapment of vasoconstrictor-potassium aluminium sulfate (0.25 %PA) and coagulation activator-calcium chloride (0.25 %Ca) into Cs (2 %) hydrogel would enhance the hemostatic property of Cs. In this work, the prepared composite hydrogel was injectable, shear thinning, cyto and hemocompatible. The 2 %Cs-0.25 %PA-0.25 %Ca composite hydrogel caused rapid blood clotting by accelerating RBC/platelet aggregation and activation of the coagulation cascade. Further, in vivo studies on rat liver and femoral artery hemorrage model showed the efficiency of 2 %Cs-0.25 %PA-0.25 %Ca composite hydrogel to achieve hemostasis in a shorter time (20 ± 10 s, 105 ± 31 s) than commercial hemostatic agents-Fibrin sealant (77 ± 26 s, 204 ± 58 s) and Floseal (76 ± 15 s, 218 ± 46 s). In in vivo toxicological study, composite hydrogel showed material retention even after 8 weeks post-surgery, therefore excess hydrogel should be irrigated from site of application. This prepared composite hydrogel based hemostatic agent has potential application in low pressure bleeding sites.

The Plasma Factor XIII Heterotetrameric Complex Structure: Unexpected Unequal Pairing within a Symmetric Complex

Factor XIII (FXIII) is a predominant determinant of clot stability, strength, and composition. Plasma FXIII circulates as a pro-transglutaminase with two catalytic A subunits and two carrier-protective B subunits in a heterotetramer (FXIII-A₂B₂). FXIII-A₂ and -B₂ subunits are synthesized separately and then assembled in plasma. Following proteolytic activation by thrombin and calcium-mediated dissociation of the B subunits, activated FXIII (FXIIIa) covalently cross links fibrin, promoting clot stability. The zymogen and active states of the FXIII-A subunits have been structurally characterized; however, the structure of FXIII-B subunits and the FXIII-A₂B₂ complex have remained elusive. Using integrative hybrid approaches including atomic force microscopy, cross-linking mass spectrometry, and computational approaches, we have constructed the first all-atom model of the FXIII-A₂B₂ complex. We also used molecular dynamics simulations in combination with isothermal titration calorimetry to characterize FXIII-A₂B₂ assembly, activation, and dissociation. Our data reveal unequal pairing of individual subunit monomers in an otherwise symmetric complex, and suggest this unusual structure is critical for both assembly and activation of this complex. Our findings enhance understanding of mechanisms associating FXIII-A₂B₂ mutations with disease and have important implications for the rational design of molecules to alter FXIII assembly or activity to reduce bleeding and thrombotic complications.

Structure functional insights into calcium binding during the activation of coagulation factor XIII A

The dimeric FXIII-A₂, a pro-transglutaminase is the catalytic part of the heterotetrameric coagulation FXIII-A₂B₂ complex that upon activation by calcium binding/thrombin cleavage covalently cross-links preformed fibrin clots protecting them from premature fibrinolysis. Our study characterizes the recently disclosed three calcium binding sites of FXIII-A concerning evolution, mutual crosstalk, thermodynamic activation profile, substrate binding, and interaction with other similarly charged ions. We demonstrate unique structural aspects within FXIII-A calcium binding sites that give rise to functional differences making FXIII unique from other transglutaminases. The first calcium binding site showed an antagonistic relationship towards the other two. The thermodynamic profile of calcium/thrombin-induced FXIII-A activation explains the role of bulk solvent in transitioning its zymogenic dimeric form to an activated monomeric form. We also explain the indirect effect of solvent ion concentration on FXIII-A activation. Our study suggests FXIII-A calcium binding sites could be putative pharmacologically targetable regions.

Factor XIII topology: organization of B subunits and changes with activation studied with single-molecule atomic force microscopy

Essentials Factor XIII is a heterotetramer with 2 catalytic A subunits and 2 non-catalytic B subunits. Structure of active and inactive factor XIII was studied with atomic force microscopy. Inactive factor XIII is made of an A2 globule and 2 flexible B subunits extending from it. Activated factor XIII separates into a B2 homodimer and 2 monomeric active A subunits. SUMMARY: Background Factor XIII (FXIII) is a precursor of the blood plasma transglutaminase (FXIIIa) that is generated by thrombin and Ca2+ and covalently crosslinks fibrin to strengthen blood clots. Inactive plasma FXIII is a heterotetramer with two catalytic A subunits and two non-catalytic B subunits. Inactive A subunits have been characterized crystallographically, whereas the atomic structure of the entire FXIII and B subunits is unknown and the oligomerization state of activated A subunits remains controversial. Objectives Our goal was to characterize the (sub)molecular structure of inactive FXIII and changes upon activation. Methods Plasma FXIII, non-activated or activated with thrombin and Ca2+ , was studied by single-molecule atomic force microscopy. Additionally, recombinant separate A and B subunits were visualized and compared with their conformations and dimensions in FXIII and FXIIIa. Results and Conclusions We showed that heterotetrameric FXIII forms a globule composed of two catalytic A subunits with two flexible strands comprising individual non-catalytic B subunits that protrude on one side of the globule. Each strand corresponds to seven to eight out of 10 tandem repeats building each B subunit, called sushi domains. The remainder were not seen, presumably because they were tightly bound to the globular A2 dimer. Some FXIII molecules had one or no visible strands, suggesting dissociation of the B subunits from the globular core. After activation of FXIII with thrombin and Ca2+ , B subunits dissociated and formed B2 homodimers, whereas the activated globular A subunits dissociated into monomers. These results characterize the molecular organization of FXIII and changes with activation.

Proline 36 of the Factor XIII Activation Peptide Plays a Crucial Role in Substrate Recognition and Zymogen Activation

The activation peptide of blood coagulation factor XIII (AP-FXIII) has important functions in stabilizing the FXIII-A₂ dimer and regulating FXIII activation. Contributions of many of its 37 amino acids to these functions have been described. However, the role of proline 36, which is adjacent to the thrombin cleavage site at Arg37, has not yet been studied in detail. We approached this question when we came across a patient with congenital FXIII deficiency in whom we detected a novel Pro36Ser mutation. We expressed the mutant FXIII-A Pro36Ser protein in Chinese hamster ovary cells and found that this mutation does not influence FXIII-A expression but significantly inhibits proteolytic activation by thrombin. The enzymatic transglutaminase activity is not affected as it can be induced in the presence of high Ca²⁺ concentrations. We performed nuclear magnetic resonance analysis to investigate AP-FXIII-thrombin interactions, which showed that the mutant Ser36 peptide binds less well to the thrombin surface than the native Pro36 peptide. The Arg37 at the P₁ position still makes strong interactions with the active site cleft but the P₄-P₂ residues (³⁴VVS³⁶) appear to be less well positioned to contact the neighbouring thrombin active site region. In conclusion, we have characterized a novel mutation in AP-FXIII representing only the fourth case of the rare FXIII-A type II deficiency. This case served as a perfect in vivo model to shed light on the crucial role of Pro36 in the proteolytic activation of FXIII-A. Our results contribute to the understanding of structure-function relationship in FXIII.

Activation of factor XIII is accompanied by a change in oligomerization state

Factor XIII A (FXIIIA) is a member of the transglutaminase enzyme family that cross-links both intra- and extracellular protein substrates. To prevent undesired cross-linking, FXIIIA is expressed as an inactive zymogen and exists intracellularly as an A₂ homodimer. In plasma, FXIII A₂ is complexed with two protective factor XIII B subunits (A₂ B₂ ) that dissociate upon activation of the zymogen. Based on limited experimental data, activated FXIII was considered a dimer of two catalytically active A subunits. However, accumulating but indirect evidence has suggested activation may lead to a monomeric state instead. In the present study, we employed analytical ultracentrifugation (AUC) to directly explore the oligomerization state of zymogen as well as active FXIIIA in solution. We first confirmed that the zymogen was a FXIIIA₂ dimer. When we activated FXIIIA nonproteolytically (by high mm Ca²⁺ ), the protein dissociated to monomers. More importantly, FXIIIA incubation with its physiological partner, the protease thrombin, led to a monomeric state as well. AUC studies of partially cleaved FXIIIA further suggested that thrombin cleavage of a single activation peptide in a zymogen dimer is sufficient to weaken intersubunit interactions, initiating the transition to monomer. The enzymatic activity of the thrombin-cleaved species was higher than nonproteolytically activated enzyme, suggesting that displacement of the activation peptide renders the FXIIIA more accessible to substrates. Thus, results provide evidence that FXIII undergoes a change in oligomerization state as part of the activation process, and emphasize the role of the activation peptide in preventing FXIIIA catalytic activity.

ENZYMES

Factor XIIIA (EC2.3.2.13).

Revisiting the mechanism of coagulation factor XIII activation and regulation from a structure/functional perspective

The activation and regulation of coagulation Factor XIII (FXIII) protein has been the subject of active research for the past three decades. Although discrete evidence exists on various aspects of FXIII activation and regulation a combinatorial structure/functional view in this regard is lacking. In this study, we present results of a structure/function study of the functional chain of events for FXIII. Our study shows how subtle chronological submolecular changes within calcium binding sites can bring about the detailed transformation of the zymogenic FXIII to its activated form especially in the context of FXIIIA and FXIIIB subunit interactions. We demonstrate what aspects of FXIII are important for the stabilization (first calcium binding site) of its zymogenic form and the possible modes of deactivation (thrombin mediated secondary cleavage) of the activated form. Our study for the first time provides a structural outlook of the FXIIIA₂B₂ heterotetramer assembly, its association and dissociation. The FXIIIB subunits regulatory role in the overall process has also been elaborated upon. In summary, this study provides detailed structural insight into the mechanisms of FXIII activation and regulation that can be used as a template for the development of future highly specific therapeutic inhibitors targeting FXIII in pathological conditions like thrombosis.

Blood coagulation factor XIII and factor XIII deficiency

Factor XIII (FXIII) is a multifunctional pro-γ-transglutaminase that, in addition to its well-known role in hemostasis, has a crucial role in angiogenesis, maintenance of pregnancy, wound healing, bone metabolism, and even cardio protection. FXIII deficiency (FXIIID) is a rare bleeding disorder (RBD) with an estimated incidence of one per two million that is accompanied by life-threatening bleeding such as umbilical cord bleeding, recurrent spontaneous miscarriage, and intracranial hemorrhage (ICH). Today, the disease is successfully managed by FXIII concentrate and recombinant FXIII for prophylaxis, management of minor and major bleeding, treatment of ICH, and successful delivery in women with recurrent pregnancy loss. Molecular analysis of patients with FXIIID revealed a wide spectrum of mutations, most frequently missense mutations in the FXIII-A subunit, with a few recurrent mutations observed worldwide. In vitro expression studies revealed that most of the missense mutations cause intracellular instability of the FXIII protein and, subsequently, FXIIID.

Viscoelasticity and Ultrastructure in Coagulation and Inflammation: Two Diverse Techniques, One Conclusion

The process of blood clotting has been studied for centuries. A synopsis of current knowledge pertaining to haemostasis and the blood components, including platelets and fibrin networks which are closely involved in coagulation, are discussed. Special emphasis is placed on tissue factor (TF), calcium and thrombin since these components have been implicated in both the coagulation process and inflammation. Analysis of platelets and fibrin morphology indicate that calcium, tissue factor and thrombin at concentrations used during viscoelastic analysis (with thromboelastography or TEG) bring about alterations in platelet and fibrin network ultrastructure, which is similar to that seen in inflammation. Scanning electron microscopy indicated that, when investigating platelet structure in disease, addition of TF, calcium or thrombin will mask disease-induced alterations associated with platelet activation. Therefore, washed platelets without any additives is preferred for morphological analysis. Furthermore, morphological and viscoelastic analysis confirmed that thrombin activation is the preferred method of fibrin activation when investigating fibrin network ultrastructure.

The activation peptide of coagulation factor XIII is vital for its expression and stability

BACKGROUND

The human activation peptide of factor XIII (AP-FXIII) comprises the first 37 amino acids of the N-terminus and holds the FXIII in an inactive state. FXIII is activated either proteolytically by cleavage of AP-FXIII by thrombin, or non-proteolytically by high calcium concentrations.

OBJECTIVE

To investigate the role of AP-FXIII in the expression and stability of FXIII.

METHODS

We cloned 13 FXIII variants with progressive truncations of AP-FXIII from the N-terminus (delN-FXIII-A), expressed them in mammalian cells, and measured their thermostability, activation, and transglutaminase activity. We also used in silico calculations to analyze the stability of hypothetical delN-FXIII dimers and to identify crucial motifs within AP-FXIII.

RESULTS

Variants with deletions longer than the first 10 amino acids and an R11Q point mutant were not expressed as proteins. In silico calculations indicated that the sequence (8) FGGR(12) R plays a substantial role in intersubunit interactions in FXIII-A2 homodimers. In agreement with this prediction, the temperature stability of delN-FXIII variants decreased with increasing length of deletion. These results may suggest a role of the N-terminus of AP-FXIII in dimer stability. Substantial sequence homology was found among activation peptides of vertebrate and even invertebrate (crustacean) FXIII-A orthologs, which further supports our conclusion.

CONCLUSIONS

We conclude that deletion of 11 or more N-terminal amino acids disrupts intersubunit interactions, which may prevent FXIII-A2 homodimer formation. Therefore, AP-FXIII plays an important role in the stability of the FXIII-A2 dimer.

The hemostatic system as a regulator of inflammation in atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial vessel wall. As part of a tightly connected cross-talk between inflammation and coagulation, there is growing evidence that the coagulation system plays a pivotal role in the development and progression of atherosclerosis. We here discuss the presence of coagulation factors in atherosclerotic lesions and the overall effects of hypercoagulability and hypocoagulability on atherosclerotic lesion formation. Moreover, we focus on the unifying common pathway of coagulation, which can be initiated by the intrinsic and extrinsic pathway of coagulation, and discuss the functions of the coagulation factors FX, thrombin, and FXIII as regulators of inflammation in atherosclerosis. In particular, we review the non-hemostatic and immune-modulatory functions of these factors in endothelial and smooth muscle cells, as well as monocytes/macrophages, but also other cells, such as dendritic cells and T cells, that may control the inflammatory process of atherosclerosis. Their multiple roles in coagulation, but also their non-hemostatic functions in different cell types in inflammation and immunity, may harbor great potential for the development of novel therapeutic approaches for treating cardiovascular disease.

Factor XIIIa generation assay: a tool for studying factor XIII function in plasma

Triggering the extrinsic coagulation pathway in plasma and using a fluorogenic factor XIIIa (FXIIIa) substrate for continuously monitoring FXIIIa activity, an FXIIIa generation curve is obtained. The parameters area under the curve (AUC), time to peak (TTP), and concentration at peak (CP) were calculated. In dilutions of normal plasma in FXIII-deficient plasma, AUC and CP showed linear dose-response relationships, whereas TTP increased from 9.9 min for 25% FXIII to 11.6 min for 100% FXIII. Three FXIII-A preparations (rFXIII, rFXIII(V34L), and cellular FXIII [cFXIII]) showed a linear dose response for AUC and CP. The TTP increased slightly for rFXIII from 13.5 to 15.0 min, but surprisingly for cFXIII TTP increased concentration dependently from 13.5 to 28.7 min. Adding 5 μg/ml FXIII-B at a concentration of 1U of FXIII-A increased the AUC for rFXIII(V34L) and cFXIII by approximately 20% and accelerated TTP from 27.3 to 20.8 min for cFVIII, indicating a supportive function of FXIII-B in orientating cFXIII-A for thrombin cleavage. A commercial assay quantifying FXIII after complete activation in a restricted time window did not reveal differences in the cFXIII preparation with or without FXIII-B. The FXIIIa generation assay provides additional information about activation and function of FXIII. This advantage was underlined in experiments with an irreversible FXIIIa inhibitor.

Characterization of Anopheles gambiae transglutaminase 3 (AgTG3) and its native substrate Plugin

Male Anopheles mosquitoes coagulate their seminal fluids via cross-linking of a substrate, called Plugin, by the seminal transglutaminase AgTG3. Formation of the "mating plug" by cross-linking Plugin is necessary for efficient sperm storage by females. AgTG3 has a similar degree of sequence identity (~30%) to both human Factor XIII (FXIII) and tissue transglutaminase 2 (hTG2). Here we report the solution structure and in vitro activity for the cross-linking reaction of AgTG3 and Plugin. AgTG3 is a dimer in solution and exhibits Ca(2+)-dependent nonproteolytic activation analogous to cytoplasmic FXIII. The C-terminal domain of Plugin is predominantly α-helical with extended tertiary structure and oligomerizes in solution. The specific activity of AgTG3 was measured as 4.25 × 10(-2) units mg(-1). AgTG3 is less active than hTG2 assayed using the general substrate TVQQEL but has 8-10× higher relative activity when Plugin is the substrate. Mass spectrometric analysis of cross-linked Plugin detects specific peptides including a predicted consensus motif for cross-linking by AgTG3. These results support the development of AgTG3 inhibitors as specific and effective chemosterilants for A. gambiae.

Substrates of Factor XIII-A: roles in thrombosis and wound healing

FXIII (Factor XIII) is a Ca2+-dependent enzyme which forms covalent ϵ-(γ-glutamyl)lysine cross-links between the γ-carboxy-amine group of a glutamine residue and the ϵ-amino group of a lysine residue. FXIII was originally identified as a protein involved in fibrin clot stabilization; however, additional extracellular and intracellular roles for FXIII have been identified which influence thrombus resolution and tissue repair. The present review discusses the substrates of FXIIIa (activated FXIII) involved in thrombosis and wound healing with a particular focus on: (i) the influence of plasma FXIIIa on the formation of stable fibrin clots able to withstand mechanical and enzymatic breakdown through fibrin–fibrin cross-linking and cross-linking of fibrinolysis inhibitors, in particular α2-antiplasmin; (ii) the role of intracellular FXIIIa in clot retraction through cross-linking of platelet cytoskeleton proteins, including actin, myosin, filamin and vinculin; (iii) the role of intracellular FXIIIa in cross-linking the cytoplasmic tails of monocyte AT1Rs (angiotensin type 1 receptors) and potential effects on the development of atherosclerosis; and (iv) the role of FXIIIa on matrix deposition and tissue repair, including cross-linking of extracellular matrix proteins, such as fibronectin, collagen and von Willebrand factor, and the effects on matrix deposition and cell–matrix interactions. The review highlights the central role of FXIIIa in the regulation of thrombus stability, thrombus regulation, cell–matrix interactions and wound healing, which is supported by observations in FXIII-deficient humans and animals.

Role of calcium in the conformational dynamics of factor XIII activation examined by hydrogen-deuterium exchange coupled with MALDI-TOF MS

Factor XIII catalyzes formation of γ-glutamyl-ε-lysyl crosslinks within fibrin clots. FXIII A(2) can be activated proteolytically with thrombin and low mM Ca(2+) or nonproteolytically with high monovalent/divalent cations along with low mM Ca(2+). Physiologically, FXIII A(2) is poised to respond to transient influxes of Ca(2+) in a Na(+) containing environment. A successful strategy to monitor FXIII conformational events is hydrogen-deuterium exchange (HDX) coupled with mass spectrometry. FXIII A(2) was examined in the presence of different cations (Ca(2+), Mg(2+), Ba(2+), Cu(2+), Na(+), TMAC(+), and EDA(2+)) ranging from 1 to 2mM, physiological Ca(2+) concentration, to 50-500mM for nonproteolytic activation. Increases in FXIII solvent exposure could already be observed at 1mM Ca(2+) for the dimer interface, the catalytic site, and glutamine substrate regions. By contrast, solvent protection was observed at the secondary cleavage site. These events occurred even though 1mM Ca(2+) is insufficient for FXIII activation. The metals 1mM Mg(2+), 1mM Ba(2+), and 1mM Cu(2+) each led to conformational changes, many in the same FXIII regions as Ca(2+). FXIII could also be activated nonproteolytically with 500mM tetramethylammonium chloride (TMAC(+)) and 500mM ethylenediamine (EDA(2+)), both with 2mM Ca(2+). These different HDX studies help reveal the first FXIII segments that respond to physiological Ca(2+) levels.