Fibrin polymerization

Bark N, Foldes Papp Z, Rigler R. The incipient stage in thrombin-induced fibrin polymerization detected by FCS at the single molecule level. Biochem Biophys Res Commun 1999 260 35-41. 

Mosesson MW. Fibrinogen and fibrin polymerization appraisal of the binding events that accompany fibrin generation and fibrin clot assembly. Blood Coagul Fibrinol 1997 8 257-267. 

The blood coagulation cascade. Each of the curved red arrows represents a proteolytic reaction, in which a protein is cleaved at one or more specific sites. With the exception of fibrinogen, the substrate in each reaction is an inactive zymogen except for fibrin, each product is an active protease that proceeds to cleave another member in the series. Many of the steps also depend on interactions of the proteins with Ca2+ ions and phospholipids. The cascade starts when factor XII and prekallikrein come into contact with materials that are released or exposed in injured tissue. (The exact nature of these materials is still not fully clear.) When thrombin cleaves fibrinogen at several points, the trimmed protein (fibrin) polymerizes to form a clot. 

Fig. 1. Basic scheme of fibrin polymerization and fibrinolysis. The clot is formed on the conversion of fibrinogen to fibrin by cleavage of the fibrinopeptides by thrombin, followed by stabilization of the network with isopeptide bonds by the transglutaminase Factor XHIa. The clot is dissolved through proteolysis by the enzyme plasmin, which is activated on the fibrin surface by plasminogen activators. This process is controlled by several inhibitory reactions (black arrows).

The crystal structures of fragment D from several recombinant fibrinogens has demonstrated that these mutant molecules are excellent models for the study of structure-function relationships, since the polypeptide chains are folded properly with only local changes (Kostelansky et al., 2002). Moreover, these studies allow testing of hypotheses about the effects of a particular mutation on structure and internal interactions within the molecule, which then can be correlated with the effects on fibrin polymerization or platelet aggregation (Kostelansky et al., 2004a,b). 

Fibrin polymerization is initiated by the enzymatic cleavage of the fibrinopeptides, converting fibrinogen to fibrin monomer (Fig. 1). Then, several nonenzymatic reactions yield an orderly sequence of macromolec-ular assembly steps. Several other plasma proteins bind specifically to the resulting fibrin network. The clot is stabilized by covalent ligation or crosslinking of specific amino acids by a transglutaminase, Factor XHIa. 

Fig. 5. Schematic diagram of complementary binding sites or knob-hole interactions in fibrin polymerization. Fibrinopeptides in the central domain cover knobs that are complementary to holes that are always exposed at the ends of the protein. When the fibrinopeptides are removed by thrombin, knob-hole interactions occur, giving rise to the two-stranded protofibril made up of half-staggered molecules.

There is evidence for the involvement of the N-terminal B/3 chain in fibrin polymerization (Pandya et at, 1985 Siebenlist et al., 1990). A recombinant fibrinogen with His substituted for Arg at the B/3 thrombin-cleavage site led to a 300-fold decrease in the rate of fibrinopeptide B release, whereas the rate of fibrinopeptide A release was normal (Moen et al., 2003). As a consequence, thrombin- or batroxobin-catalyzed or desA monomer polymerization was impaired, due to the histidine substitution itself. Thus, it appears that the N-terminus of the B/3 chain is involved in the lateral aggregation of normal desA protofibrils. 

Kostelansky, M. S., Lounes, K. C., Ping, L. F., Dickerson, S. K., Gorkun, O. V., and Lord, S. T. (2004b). Calcium-binding site beta 2, adjacent to the b polymerization site, modulates lateral aggregation of protofibrils during fibrin polymerization. Biochem. 43, 2475-2483. 

Weisel, J. W., and Nagaswami, C. (1992). Computer modeling of fibrin polymerization kinetics correlated with electron microscope and turbidity observations Clot structure and assembly are kinetically controlled. Biophys. J. 63, 111-128. 

Several new compounds have been reported that affect the formation of a fibrin clot. Aromatic diamidines, such as, 21, were reported to inhibit several proteolytic enzymes including thrombin.74 Concanavalin A (a globulin protein from the jack bean) inhibits fibrin formation by inhibiting the lipoprotein cofactor in the production of thrombin and thus decreasing the rate of thrombin production.75 Several antibiotics (penicillins and cephalosporins) have been reported to affect fibrin clot formation as well as platelet function. Cephalothin (22) has been shown to delay fibrin polymerization and thus prolong the activated partial thromboplastin time (APTT) and thrombin time tests.78... 

Dietler, G. Fibrin polymerization a combination of light scattering with measurements of fibrinopeptide release. Diss. ETH No. 7819,1985 (Department of Physics, Swiss Federal Institute of Technology, CH8092 Ziirich). 

Thrombin Time Functional evaluation of fibrinogen concentration, polymerization Fibrinogen, antithrombin/(/icpan>i) Fibrinogen concentration and fibrin functionality (fibrinopeptide cleavage, fibrin polymerization) Heparin causes artifactual prolongation because of enhanced thrombin inactivation by antithrombin... 

Standeven KF, Ariens RA, Whitaker P et al. The effect of dimethylbiguanide on thrombin activity, FXni activation, fibrin polymerization, and fibrin clot formation. Diabetes 2002 51 189-197. 

Paul A. Janmey received an AB degree from Oberlin College in 1976 and a PhD degree in physical chemistry from the University ofWisconsin in 1982 (for his work on fibrin polymerization, under the guidance of J. D. Ferry). A postdoctoral fellowship in the Hematology Unit of Massachusetts General Hospital motivated application of methods of polymer physics to the cytoskeleton. Since then his lab has studied the viscoelastic properties of biopolymer networks and the regulation of cytoskeletal and extracellular matrix assembly. 

Boryczko, K., Dzwinel, W., and Yuen, D.A., Modeling fibrin polymerization in blood flow with discrete-particles. Comp. Models Prog. Biomed., 75, 181 194, 2004. 

Pizano, J. J. Finlayson, J. S. Peyton, M. P. Cross-Link in Fibrin Polymerized by Factor 13 epsilon-(gamma-glutamyl)lysine. Science, 1968,60,1892. 

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