Binding of β2-glycoprotein I (β2-GPI)-dependent anticardiolipin antibodies (aCL) derived from antiphospholipid syndrome (APS) is significantly reduced in aCL ELISA due to loss of the phospholipid (PL) binding property of β2-GPI by plasmin treatment. In the present study, the treatment generated a nicked form of β2-GPI and resulted in loss of antigenicity for the autoantibodies detected in ELISA, using an β2-GPI directly adsorbed polyoxygenated carboxylated plate, the assay system of which was not related to PL binding. The nicked form bound to neither Cu2+-oxidized low-density lipoprotein (oxLDL) nor to β2-GPI-specific lipid ligands isolated from oxLDL, the result being a complete loss of subsequent binding of anti-β2-GPI autoantibodies. The conformational change in the nicked domain V was predicted from its intact structure determined by an X-ray analysis (implemented in Protein Data Bank: 1C1Z), molecular modeling and epitope mapping of a monoclonal anti-β2-GPI antibody, i.e. Cof-18, which recognizes the related structure. The analysis revealed that novel hydrophobic and electrostatic interactions appeared in domain V after the cleavage, thereby affecting the PL binding of β2-GPI. Such a conformational change may have important implications for exposure of cryptic epitopes located in the domains such as domain IV.
- Anti-β-glycoprotein I antibodies
- Antiphospholipid syndrome
- Epitope mapping
ASJC Scopus subject areas
- Immunology and Allergy