Papers by Keyword: Fibrin Polymerization

Abstract: Cleavage of carbohydrate chains linked to fibrinogen molecule results in an acceleration of fibrin polymerization, fibrin gel formation, by promoting the lateral aggregation of protofibrils. Sialic acid at the unreduced terminus of carbohydrate chain plays an essentially important role in the lateral aggre-gation. Fibrin polymerization is significantly affected by the solvent condition, e.g., pH and ionic strength. Terminal sialic acid are supposed to interact with amino terminal region of Bβ chain, in which there are many basic amino acid residues, and thus such interactions are expected to be electrostatic. In order to clarify whether the electrostatic interactions are essential for lateral aggregation, we examined temporal growth of fibrin polymerization of deglycosylated fibrinogen at high NaCl concentration. Marked acceleration of lateral aggregation was observed in deglycosylated fibrinogen even at high NaCl concentration where lateral aggregation was significantly inhibited in intact fibrinogen. These results suggest specific interactions of terminal sialic acid of the carbohydrate chain with the central E region of fibrinogen molecule, which may be important for the regulation of lateral aggregation rather than electrostatic interactions between the terminal sialic acids and the amino terminal region of Bβ chain.

Abstract: Acceleration of fibrin polymerization occurs by the cleavage of sialic acids at the nonreducing terminal ends of N-linked carbohydrate chains as well as the cleavage of the entity of carbohydrate chains. In order to characterize and clarify the role of terminal sialic acid in the fibrin polymerization, mixing effects of desialylated fibrinogen with the intact one on the polymerization behavior were investigated by turbidity measurements in the course of polymerization. Marked accelerated fibrin polymerization was observed for the mixing of even a little amount of desialylated fibrinogen. Cleavage of the terminal sialic acid resulted in almost the equivalent accelerating effect to those of the deglycosylated fibrinogen, in which the entity of N-linked carbohydrate chain was cleaved. These results suggest that the terminal sialic acids regulate the fibrin polymerization in an inhibitory manner, and the cleavage of them induces the switchover from the protofibril growth to the lateral aggregation of fibrin polymerization process, resulting in the preferential fibrin polymerization.

Abstract: Fibrin polymerization proceeds in a stepwise manner. In the first step, fibrinogen-to-fibrin conversion is triggered by the enzymatic fibrinopeptide release and protofibril formation/growth proceeds. In the following second step, lateral aggregation of the protofibrils occurs resulting in the network formation. Switchover from the first step to the second one can regulate the resultant network structure, and the lateral aggregation is considered to be induced by the interaction between the αC regions of two adjacent protofibrils. In order to clarify the characteristics of this interaction, we examined the cross-sectional diameter D_C in addition to the hydrodynamic diameter (Stoke diameter) of fibrinogen molecule in various solution conditions. Cross-sectional diameter of intact fibrinogen was 4.7 nm in agreement with the molecular structure. On the other hand, fragment-X, in which the αC regions are deleted, had smaller D_C of 4.2 nm. This means that the αC regions snuggle up to the molecular backbone, which is consistent with the model that the termini of the αC regions are tethered to the central E-region in the intact fibrinogen. On the other hand, fibrinogen at pH 3 had a cross-sectional diameter of 4.0 nm, which is further smaller than that of fragment-X. This is accounted for by the scheme that the αC regions are released from the central region, because side chains of Asp and Glu residues have neutral charge at pH 3. With the increase of ionic strength up to 150 mM at pH 3, fibrinogen molecules become to aggregate resulting in huge aggregated particles. Our results suggest that the released αC regions can interact attractively with each other through the hydrophobic interaction, which supports the proposed scheme of fibrin polymerization.