Evidence of a phospholipid binding species within human fibrinogen preparations

Fibrinogen has been reported to interact with phospholipid; however, the pr operties of this binding interaction have not been characterized. Purified preparations of human fibrinogen bound to small unilamellar vesicles contai ning phosphatidylserine (PS) as measured by light scattering and radioisoto pe filtration. Binding to 100% PS was saturable (apparent K-d=5 mu M, B-max =1.9 g protein/g lipid), reversible, and involved a minor subfraction of th e fibrinogen preparation (3-6% of total protein). Fibrinogen interacted min imally with phosphatidylinositol, and not at all with pure phosphatidylchol ine (PC) or PC vesicles containing 5% glycosphingolipid (lactosylceramide, ganglioside GM3, ganglioside GD3), Binding efficiency decreased as the PS c ontent of vesicles was diluted with PC. Calcium chloride (2 mM) enhanced pr otein binding to PS, which was reversed by EDTA. Fibrin clot formation almo st quantitatively precipitated the PS binding activity. PS, but not PC, inc reased the final turbidity of fibrin clots. Computerized sequence analysis of fibrinogen revealed three candidate acidic phospholipid binding motifs l ocated at position 143-210 in the alpha chain, and positions 59-77 and 101- 139 in the beta chain. Further study of the PS binding activity of fibrinog en may lead to new insights about fibrinogen function. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.