The sequence 581Ser-610Val in the fibrinogen Aα chain is responsible for the formation of complexes between plasminogen and αC-regions of fibrin(ogen).

OBJECTIVE

This study aimed to identify the binding sites for plasminogen (Pg) and its kringle-containing fragments within the αC-region of fibrin(ogen). This investigation is crucial while the conversion of fibrinogen into fibrin induces conformational changes that expose binding sites for Pg and tissue-type Pg activator (tPA), facilitating effective zymogen activation on the fibrin surface.

METHODS

Two C-terminal fragments of the Aα chain ‒ 45 kDa (225Val-610Val) and 40 kDa (225Val-580Lys), were obtained through plasmin hydrolysis of human fibrinogen and subsequently characterized using MALDI TOF mass spectrometry. The interactions of Glu-Pg and Lys-Pg, as well as Pg kringle fragments (K1-3, K4, and K5), with the obtained αC truncated polypeptides were analyzed using ELISA and Western blot techniques with the use of specific antibodies.

RESULTS

It was demonstrated that Pg and its fragments K1-3, K4, and K5 interact exclusively with the 45-kDa fragment (225Val-610Val) of the αC region of fibrinogen with high affinity in a concentration-dependent manner (K values for Glu-Pg = 7.10 × 10 M, Lys-Pg = 6.01 × 10 M, K1-3 = 1.08 × 10 M, K4 = 5.06 × 10 M, and K5 = 2.50 × 10 M). This fragment, unlike the 40-kDa polypeptide (225Val-580Lys), contains the α581Ser-610Val sequence.

CONCLUSIONS

It was shown that the sequence 581Ser-610Val of fibrinogen Aα-chain, which becomes exposed during the conversion of fibrinogen to fibrin, is essential for the formation of complexes between Pg and αC regions of fibrin(ogen), thereby contributing to the initiation and regulation of fibrinolysis.