THE RELATIONSHIP BETWEEN THE FIBRINOGEN D DOMAIN SELF-ASSOCIATION CROSS-LINKING SITE (GAMMA-XL) AND THE FIBRINOGEN DUSART ABNORMALITY (A-ALPHA R554C-ALBUMIN) - CLUES TO THROMBOPHILIA IN THE DUSART-SYNDROME/

Cross-linking of fibrinogen at its COOH-terminal gamma chain cross-lin king site occurs in the presence of factor XIIIa due to self-associati on at a constitutive D domain site (''gamma XL''). We investigated the contribution of COOH-terminal regions of fibrinogen Act chains to the gamma XL site by comparing the gamma chain cross-linking rate of inta ct fibrinogen (fraction I-2) with that of plasma fraction I-9, plasmic fraction I-9D, and plasmic fragment D-1, which lack COOH-terminal A a lpha chain regions comprising similar to 100, similar to 390, and 413 residues, respectively, The cross-linking rates were I-2 > I-9 > I-9D = D-1, and indicated that the terminal 100 or more ACL chain residues enhance gamma XL site association. Fibrinogen Dusart, whose structural abnormality is in the COOH-terminal ''alpha C'' region of its A alpha chain (A alpha R554C-albumin), is associated with thrombophilia (''Du sart Syndrome''), and is characterized functionally by defective fibri n polymerization and clot structure, and reduced plasminogen binding a nd tPA-induced fibrinolysis, In the presence of XIIIa, the Dusart fibr inogen gamma chain cross-linking rate was about twice that of normal, but was normalized in proteolytic fibrinogen derivatives lacking the A alpha chain abnormality, as was reduced plasminogen binding. Electron microscopy showed that albumin-bound Dusart fibrinogen ''alpha C'' re gions 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 A alpha chain associations pro moted by untethered Dusart fibrinogen aC domains. We conclude that enh anced Dusart fibrinogen self-assembly is mediated through its abnormal alpha C domains, leads to increased gamma XL self-association and gam ma chain cross-linking potential, and contributes to the thrombophilia that characterizes the ''Dusart Syndrome.'' (J. Clin. Invest. 1996. 9 7:2342-2350.)