title: Localization of segments essential for polymerization and for calcium binding in the gamma-chain of human fibrinogen.
abstract: We have isolated an intermediate plasmic degradation product, D2, of fibrinogen that does not inhibit the polymerization of fibrin monomer but does bind Ca2+. Fibrinogen was digested to a limited extent with plasmin in the presence of Ca2+, and a "large" fragment D (fragment D1A) was isolated with a gamma-chain remnant consisting of residues 63-411. Fragment D1A was digested further in the presence of Ca2+, yielding fragment D1 (with its gamma-chain containing residues 86-411). The digestion of fragment D1 [in the presence of ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) to complex Ca2+] led to a gradual shortening of the carboxyl-terminal portion of the gamma-chain. Fragment D2 (with its gamma-chain containing residues 86-335/356) was isolated from an intermediate digest in the presence of EGTA. The Lys-338-Cys-339 peptide bond of the gamma-chain is intact in this preparation of D2, even though it is split in the isolated peptide gamma303-355 (with an intact disulfide bond at Cys-326-Cys-339). Fragment D2 does not interfere with the polymerization of fibrin monomer, whereas fragment D1 is a potent inhibitor of this polymerization. We conclude that the gamma-chain segment 356/357-411, present in fragment D1 but absent from fragment D2, is essential for maintenance of a polymerization site located in the outer (D) nodule of fibrinogen. This segment (356/357-411) is longer than two shorter ones reported earlier [Olexa, S.A., & Budzynski, A. Z. (1981) J. Biol. Chem. 256, 3544-3549; Horwitz, B.H., Váradi, A., & Scheraga, H.A. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 5980-5984]; the data for the earlier reports are reinterpreted here. Finally, fragment D2 possesses a single Ca2+ binding site, as revealed by equilibrium dialysis binding studies. Since fragment D3 (with its gamma-chain containing residues 86-302) fails to bind Ca2+, we conclude that segment gamma 303-355/356 plays a crucial role in Ca2+ binding.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D005337:Fibrin / Q000378:metabolism; D005340:Fibrinogen / Q000378:metabolism*; D005341:Fibrinolysin / Q000378:metabolism; D006801:Humans; D046911:Macromolecular Substances; D010446:Peptide Fragments / Q000302:isolation & purification / Q000378:metabolism; D011485:Protein Binding
chemical_list: D000596:Amino Acids; D046911:Macromolecular Substances; D010446:Peptide Fragments; C027539:fibrinopeptides gamma; D005337:Fibrin; D005340:Fibrinogen; D005341:Fibrinolysin; D002118:Calcium