Beta-2-glycoprotein 1 Rabbit Polyclonal Antibody

Beta-2-glycoprotein 1 (β2-GPI), also known as apolipoprotein H, is a plasma glycoprotein of 326 amino acids organized into five complement control protein (CCP) domains, with a molecular weight of approximately 43–50 kDa depending on glycosylation. The first four domains share the conserved CCP fold, while the fifth domain is structurally distinct, containing a six-residue insertion, a 19-residue C-terminal extension, and a large positively charged patch that mediates high-affinity binding to anionic phospholipids such as cardiolipin and phosphatidylserine. In plasma, β2-GPI adopts a circular conformation in which domain I interacts with domain V; upon binding to anionic surfaces, it opens into an elongated J-shaped or "hockey stick" conformation that exposes the epitope in domain I recognized by pathogenic autoantibodies. Clinically, β2-GPI is the primary antigen in antiphospholipid syndrome (APS), an autoimmune disorder characterized by arterial, venous, or microvascular thrombosis and pregnancy morbidity. Anti-β2-GPI antibodies, particularly those targeting domain I, are included in the laboratory classification criteria for APS and contribute to a prothrombotic state by activating endothelial cells, platelets, and monocytes, upregulating tissue factor, and disrupting fibrinolysis. Beyond its role in APS, β2-GPI participates in physiological processes including clearance of lipopolysaccharide and apoptotic cell remnants, complement regulation, and modulation of coagulation, with many of these homeostatic functions localized to domain V.