A1-A1 mutant with improved binding and inhibition of beta2GPI/antibody complexes in antiphospholipid syndrome

• Published in: The FEBS journal Vol. 282; no. 5; pp. 864 - 873
• Main Authors: Kolyada, Alexey, Karageorgos, Ioannis, Mahlawat, Pardeep, Beglova, Natalia
• Format: Journal Article
• Language: English
• Published: 27.01.2015
• ISSN: 1742-464X; 1742-4658
• DOI: 10.1111/febs.13185

Beta2-glycoprotein I (β2GPI) is the most common antigen for autoimmune antibodies in antiphospholipid syndrome (APS). Thrombosis is a clinical feature of APS. We made a molecule (A1-A1) that consists of two identical β2GPI-binding modules from ApoE receptor 2. A1-A1 binds to β2GPI/anti-β2GPI antibody complexes preventing their association with ApoER2 and anionic phospholipids, and reducing thrombus size in the mouse model of APS. Here, we describe a mutant of A1-A1 (mA1-A1ND) with improved affinity for β2GPI. mA1-A1ND inhibits the binding of β2GPI to cardiolipin in the presence of anti-β2GPI antibodies and inhibits β2GPI/antibody complexes in plasma samples of APS patients affecting the clotting time. Inhibition of the clotting time demonstrates the presence of soluble β2GPI/anti-β2GPI antibody complexes in patients’ plasma. These complexes either already exist in patients’ plasma or form rapidly in the vicinity of phospholipids. All members of the LDL receptor family can bind β2GPI. Modelling studies of A1 in a complex with domain V of β2GPI (β2GPI-DV) revealed two possible orientations of a ligand-binding module from lipoprotein receptors on β2GPI-DV. In both orientations, the ligand-binding module interferes with the binding of β2GPI to anionic phospholipids, however it interacts with two different though overlapping sets of lysine residues in β2GPI-DV, depending on the orientation.