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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2005;25:2679.)
© 2005 American Heart Association, Inc.

Thrombosis

Fibrinogen Contains Cryptic PAI-1 Binding Sites That Are Exposed on Binding to Solid Surfaces or Limited Proteolysis

Katarzyna Smolarczyk; Joanna Boncela; Jacek Szymanski; Ann Gils; Czeslaw S. Cierniewski

From the Center of Medical Biology (K.S., J.B., C.S.C.), Polish Academy of Sciences, Lodz; the Department of Molecular and Medical Biophysics (J.S., C.S.C.), Medical University in Lodz, Poland; and the Laboratory for Pharmaceutical Biology and Phytopharmacology (A.G.), Katholieke Universiteit Leuven, Belgium.

Correspondence to Czeslaw S. Cierniewski, PhD, Department of Medical and Molecular Biophysics, Medical University in Lodz, 92-213 Lodz, 6/8 Mazowiecka St. E-mail cciern{at}zdn.am.lodz.pl

Objective— In this work, we identified the fibrinogen sequence that on exposure serves as the primary binding site for functionally active PAI-1 and to a lesser extent for its latent form. In contrast, this site only weakly interacts with PAI-1 substrate.

Methods and Results— The binding site is located in the N-terminal (20-88) segment of fibrinogen, in the region exposed on (1) adsorption of fibrinogen to solid surfaces; (2) the release of fibrinopeptide A during thrombin conversion of fibrinogen to fibrin; and (3) plasmin degradation of fibrinogen. This region was first identified by the yeast 2-hybrid system, then its binding characteristics were evaluated using the recombinant (16-120) fragment and its shorter version, the (20-88) fragment, in a solid phase binding assay and plasmon surface resonance measurements. Because fibrinogen fragment E does not bind PAI-1, it suggests that sequences of A chain interacting with PAI-1 are located in the N-terminal part of the (20-88) segment.

Conclusions— Therefore, PAI-1 directly bound to the (20-88) and thus concentrated in fibrinogen/fibrin, particularly at sites of injury and inflammation, may account for the recent observations that both its active and latent forms stimulate cell migration and wound healing.

We showed that PAI-1 is directly bound to the (20-88) and thus its concentration on fibrinogen/fibrin, particularly at sites of injury and inflammation, may account for the recent observations that both its active and latent forms stimulate cell migration and wound healing.

Key Words: conformational changes • fibrinogen • PAI-1 binding sites • proteolysis