Subunit Structure of Human Fibrinogen, Soluble Fibrin, and Cross-Linked Insoluble Fibrin

Abstract

Abstract. The three unique polypeptide chains of human fibrinogen differ significantly in molecular weight. Cross-linkage of fibrin by fibrin-stabilizing factor results in the rapid formation of cross-links between y-chains and a slower formation of cross-links between a-chains. p-Chains are not involved directly in the cross-linking of fibrin. Reduced, cross-linked fibrin contains uncrosslinked i-chains, dimers of y-chain, and higher polymers of a-chain. Although it is uncertain whether the y-,y dimers are formed by chains in different molecules of fibrin, the polymers of a-chain in fibrin can only be accounted for by crosslinkage of a-chains in different molecules. The nature of cross-linkage among the subunits in fibrin can account well for the three-dimensional, covalent structure of cross-linked, insoluble fibrin.Human fibrinogen, which has a molecular weight of approximately 330,000, contains three pairs of different polypeptide subunits (a, Al, y) and may be designated by the polypeptide chain formula a38272.1-4 The three chains are combined covalently through disulfide bonds and differ in amino acid sequence and molecular weight. It has been estimated that the molecular weights of the a-, (3-, and 7-chains are 63,500, 56,000, and 47,000, respectively.4 Fibrin is formed when thrombin acts on fibrinogen and cleaves specific peptide bonds in the a-and ,8-chains, thereby releasing low molecular weight peptides. Thrombin action alone produces fibrin which is less soluble than fibrinogen but is soluble at low pH or in concentrated solutions of urea or guanidine hydrochloride. Such fibrin is termed noncross-linked, soluble fibrin. Soluble fibrin is converted to cross-linked, insoluble fibrin by a transpeptidase, termed fibrin-stabilizing factor (FSF), which catalyzes the formation of new amide bonds between e-amino groups of lysine and carboxamido groups of glutamine in the subunit chains.5 Thus, cross-linked, insoluble fibrin, after reduction of its disulfide bonds, contains higher molecular weight subunits than fibrinogen. Chen and Doolittle6 concluded that reduced, cross-linked bovine fibrin contains y-7y as well as a--y dimers, whereas Lorand and co-workers found mainly a--y dimers.7 8 Similarly, Takagi and Iwanaga9 suggest that two to four 7-chains are cross-linked in insoluble fibrin.We wish to report here the results of studies on the subunit structure of human fibrinogen and cross-linked, insoluble, human fibrin. During the course of the 738

Fibrinogen splice variation and cross-linking: Effects on fibrin structure/function and role of fibrinogen γ′ as thrombomobulin II

“…3B), which affect the overall structure and stability of the fibrin mesh [25]. While factor XIII is able to cross-link both fibrin -and -chains, the kinetics is different between the two chains, with the -chains being cross-linked at a faster rate than the -chains [26,27].…”

Partial Characterization of Oat and Rye Phytochrome

“…Aliquots were then taken and added directly to the gel sample buffer (0.1% SDS 0.01 M NaPB, pH 7.2), generally in a 10: 1 dilution, giving S to 10 ,ug of protein/gel. Total sample volume was 50 [1. In some cases, denaturation was performed with hot 6 M guanidine hydrochloride (100 C, 4-5 min), followed by alkylation with iodoacetamide as described (53,58 (35).…”

Functional analysis of fibrin γ-chain cross-linking by activated factor XIII: determination of a cross-linking pattern that maximizes clot stiffness

“…During clot formation, at the early stages of polymerization, cross-linking occurs within emerging protofibrils between ␥K406 and ␥Q398 and/or ␥Q399, resulting in the formation of ␥-dimers. [5][6][7] Multiple cross-linking between fibrin ␣-chains results in the formation of ␣-polymers. 6 Over time, FXIIIa has been shown to generate cross-linked chain structures containing various combinations of ␣-and/or ␥-chains; mainly these are thought to be ␣ n , 8 but ␥ 3 , ␥ 4 , and hybrid ␣ p ␥ q (n, p, and q ϭ 1, 2, 3, respectively, and so forth) are also known to occur.…”

“…[5][6][7] Multiple cross-linking between fibrin ␣-chains results in the formation of ␣-polymers. 6 Over time, FXIIIa has been shown to generate cross-linked chain structures containing various combinations of ␣-and/or ␥-chains; mainly these are thought to be ␣ n , 8 but ␥ 3 , ␥ 4 , and hybrid ␣ p ␥ q (n, p, and q ϭ 1, 2, 3, respectively, and so forth) are also known to occur. 9,10 The effect of these different cross-linking formations on fibrin clot function has not been fully clarified.…”