Abstract
The binding between complementary polymerization sites of fibrin monomers plays an essential role in the formation of the fibrin clot. One set of polymerization sites involved in the interaction of fibrin monomers is believed to pre-exist in fibrinogen, while the complementary set of binding sites is exposed after the cleavage of fibrinopeptides from fibrinogen. The polymerization sites present in fibrinogen and its derivatives mediate their binding to fibrin. Although the binding of fibrinogen and its derivatives to fibrin have been qualitatively studied, there has been no systematic, quantitative investigation of their interaction with forming or preformed clots. In the present study, the binding of fibrinogen and fragments DD, D1, and E1 was measured using a sonicated suspension of plasminogen- and thrombin-free human cross-linked fibrin as a model of a preformed clot. Dissociation constants of 0.056, 0.19, and 2.44 microM, and the number of binding sites corresponding to 0.10, 0.21, and 0.13/fibrin monomer unit of fibrin polymer were found for fibrinogen, fragment DD, and fragment D1, respectively. Fragment E1 did not bind to sonicated noncross-linked or cross-linked fibrin suspensions. However, it was bound to forming fibrin clots as well as to fibrin-Celite, suggesting that the binding sites on fibrin involved in the interaction with fragment E1 may have been altered upon sonication. Affinity chromatography of various fibrinogen derivatives on a fibrin-Celite column showed that only part of the bound fragment DD was displaced by arginine, whereas fragments D1 and E1 were completely eluted under the same conditions. The results indicate that interaction of fibrinogen with the preformed fibrin clots is characterized by affinity in the nanomolar range and that binding between fibrin monomers, in the process of clot formation, could be characterized by even a higher affinity.
Highlights
0.056, 0.19, and 2.44 p ~ an, d the number of binding fragments Dl and ES,which constitute the end and central sites corresponding to 0.10,0.21a,nd 0.13Ifibrin mon- regions of the molecule, respectively
Thrombin catalyzes the conversion of fibrinogen to fibrin monomer which spontaneously polymerizesin ahalf-staggered manner to form a three-dimensional network of fibers [1].Electron microthrombus in vivo andto elucidate the regulatory role of fibrinogen and fibrin fragments on the propagation of the fibrin network
To obtain fibrin-Celite, fibrinogen was clotted in the presence of Celite and washed on sist of subunits similar in size to the individual elongated structures.Neither protofibrils nor normal fiber networks, consisting of cylindrical, branched fibers, were observed
Summary
From the Departmentof Biochemistry, Temple UniversitySchool of Medicine, Philadelphia, Pennsylvania 19140. The binding between complementary polymerizatisocnope data provide evidence that initial polymers consist of sites of fibrin monomers plays an essential role in the double-stranded protofibrils [2]. The latter arekept together formation of the fibrin clotO, ne set of polymerization by interaction of complementary polymerization sites on fisites involved in the interactionof fibrin monomers is brin monomer molecules that are spatially organizedin afacebelieved to pre-exist in fibrinogen, while thecomple- to-face manner[3,4,5,6]. The dataprovide the quantitative basis for the use of fragments with affinity for fibrin as thrombus-specific molecular markers
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