The relationship between the fibrinogen D domain self-association/cross-linking site (gammaXL) and the fibrinogen Dusart abnormality (Aalpha R554C-albumin): clues to thrombophilia in the "Dusart syndrome".

Abstract

Cross-linking of fibrinogen at its COOH-terminal gamma chain cross-linking site occurs in the presence of factor XIIIa due to self-association at a constitutive D domain site ("gammaXL"). We investigated the contribution of COOH-terminal regions of fibrinogen Aalpha chains to the gammaXL site by comparing the gamma chain cross-linking rate of intact fibrinogen (fraction I-2) with that of plasma fraction I-9, plasmic fraction I-9D, and plasmic fragment D1, which lack COOH-terminal Aalpha chain regions comprising approximately 100, approximately 390, and 413 residues, respectively. The cross-linking rates were I-2 > I-9 > 1-9D = D1, and indicated that the terminal 100 or more Aalpha chain residues enhance gammaXL site association. Fibrinogen Dusart, whose structural abnormality is in the COOH-terminal "alphaC" region of its Aalpha chain (Aalpha R554C-albumin), is associated with thrombophilia ("Dusart Syndrome"), and is characterized functionally by defective fibrin polymerization and clot structure, and reduced plasminogen binding and tPA-induced fibrinolysis. In the presence of XIIIa, the Dusart fibrinogen gamma chain cross-linking rate was about twice that of normal, but was normalized in proteolytic fibrinogen derivatives lacking the Aalpha chain abnormality, as was reduced plasminogen binding. Electron microscopy showed that albumin-bound Dusart fibrinogen "alphaC" regions were located in the vicinity of D domains, rather than at their expected tethered location near the fibrinogen E domain. In addition, there was considerable fibrinogen aggregation that was attributable to increased intermolecular COOH-terminal Aalpha chain associations promoted by untethered Dusart fibrinogen aC domains. We conclude that enhanced Dusart fibrinogen self-assembly is mediated through its abnormal alphaC domains, leads to increased gammaXL self-association and gamma chain cross-linking potential, and contributes to the thrombophilia that characterizes the "Dusart Syndrome."

Fibrinogen Otago: a major α chain truncation associated with severe hypofibrinogenaemia and recurrent miscarriage

“…In fibrinogen Dusart extensive studies have shown that the point mutation Aa 554Arg → Cys results in abnormal lateral aggregation, causing thinner fibrin fibres with significantly decreased gel porosity and increased clot rigidity (Koopman et al, 1993;Siebenlist et al, 1993;Collet et al, 1993). It has also recently been shown that the mutation in fibrinogen Dusart introduces a tendency for the molecules to pre-assemble (Mosesson et al, 1996), and it has been suggested that this characteristic, together with the changes to clot architecture, are the main factors contributing to the high incidence of embolism found in affected individuals. Interestingly, although both these variants arise from point mutations in the aC domain, they have opposite effects on clot structure, indicating that amino acid residues in this region are critical to the function of the aC domain.…”

Fibrin clot structure in patients with congenital dysfibrinogenaemia

“…In this study, the FGA Arg573Cysmutation showed an abnormal fibrin network with thin fibres and a very dense clot, resulting in greater resistance to fibrinolysis. Several studies have shown reduced plasminogen binding for this fibrinogen variant, impaired tPA-induced fibrinolysis [11,37] and increased XL selfassociation and -chain cross-linking [38]. However, for most other cases of thrombosis-related dysfibrinogenaemia, the molecular anomaly is probably not directly responsible for the vascular event but rather a contributing factor to the overall haemostatic balance.…”

Analysis of plasmin generation and clot lysis of plasma fibrinogen purified from a heterozygous dysfibrinogenemia, BβGly15Cys (Hamamatsu II)

“…Five independent families with AR554C-albumin binding have been identified and, strikingly, all propositi have presented with thrombosis [26]. Additionally, in vitro studies with the AR554C fibrinogen have demonstrated that impaired fibrinolysis, thinner and many branched fibers, increased clot stiffness, and an increased cross-linking potential probably explain the thrombosis and embolism seen in the families afflicted [22,[27][28][29][30]. It is interesting that for the BArg14Cys variants, which are the immediate vicinity of BGly15 residue and with a potential albumin binding (demonstrated in the propositus of Ijmuiden [12]; however, no others have been analyzed), severe thrombosis such as deep venous thrombosis, pulmonary embolism, or cerebral infarction has been reported in 6 out of the 8 families [4, [10][11][12][13][14][15][16].…”