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Characterization of b2-Glycoprotein I Binding to Phospholipid Membranes

Journal: Thrombosis and Haemostasis
ISSN: 0340-6245
Issue: 1998: 80/4 (Oct) pp.531-725
Pages: 610-614

Characterization of b2-Glycoprotein I Binding to Phospholipid Membranes

Mark F. Harper (1) , Peter M. Hayes (1) , Barry R. Lentz (2) , Robert A. S. Roubey (1)
From the (1) Division of Rheumatology and Immunology, Department of Medicine, and (2) Department of Biochemistry and Biophysics, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA

Summary

The plasma protein b2-glycoprotein I (b2 -GPI) is a major target of autoantibodies in patients with the antiphospholipid syndrome. To understand the physiological function of b2 -GPI and its potential role in the pathophysiology of the antiphospholipid syndrome, the binding of b2-GPI to phospholipid membranes was characterized. The interaction of b2-GPI with unilamellar vesicles containing varying amounts of acidic phospholipids with phosphatidylcholine (PC) was measured at equilibrium via relative light scattering. Analysis of binding isotherms gave apparent Kd values ranging from approximately 5.0 to 0.5 mM over a range of 5-20 mol % anionic phospholipid. Inhibition of binding by increasing ionic strength and Ca2+ ions suggests that binding is primarily electrostatic. These data indicate that b2-GPI binding to membranes with physiological anionic phospholipid content is relatively weak in comparison to plasma coagulation proteins, suggesting that b2-GPI does not function as a physiological anticoagulant based on its phospholipid-binding properties.