Structural organization of C-terminal parts of fibrinogen k-chains

There is a widespread opinion that about 400 residue-long C-terminal parts of both the AW chains in fibrinogen do not form a compact ordered structure since they are hydrolyzed too fast at treatment of the molecule by proteolytic enzymes [l]. However, our calorimetric study of fibrinogen melting and of its fragments have shown that parts of this molecule which are removed on the early stage of its degradation at proteolysis have a cooperative structure which melts at heating with a slight, but quite noticeable heat effect [2]. This heat effect is largely screened by a much more pronounced effect of melting of the other parts of the molecule. Thus, in our first study we did not succeed in analyzing it quantitatively to get more definite information on the structure formed by the easily removable parts of fibrinogen. This has been done now and we here report the obtained results showing that two domains formed by the C-terminal part of both AW chains strongly interact with each other as they are in direct contact between themselves in the native fibrinogen molecule.