title: An A1-A1 mutant with improved binding and inhibition of β2GPI/antibody complexes in antiphospholipid syndrome.
abstract: β2 glycoprotein I (β2GPI) is the most common antigen for autoimmune antibodies in antiphospholipid syndrome (APS). Thrombosis is a clinical feature of APS. We created a molecule (A1-A1) that consists of two identical β2GPI-binding modules from ApoE receptor 2 (ApoER2). A1-A1 binds to 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 the binding to phospholipids in plasma samples of APS patients, affecting the clotting time. Reduction of the clotting time demonstrates the presence of soluble β2GPI/antibody complexes in patients' plasma. These complexes either already exist in patients' plasma or form rapidly in the proximity to phospholipids. All members of the low-density lipoprotein receptor family bind β2GPI. Modeling studies of A1 in a complex with domain V of β2GPI (β2GPI-DV) revealed two possible modes of interaction of a ligand-binding module from lipoprotein receptors with β2GPI-DV. In both orientations, the ligand-binding module interferes with binding of β2GPI to anionic phospholipids; however, it interacts with two different but overlapping sets of lysine residues in β2GPI-DV, depending on the orientation.
authors.affiliation: Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA.
authors.forename: Alexey
authors.initials: A
authors.lastname: Kolyada
authors.forename: Ioannis
authors.initials: I
authors.lastname: Karageorgos
authors.forename: Pardeep
authors.initials: P
authors.lastname: Mahlawat
authors.forename: Natalia
authors.initials: N
authors.lastname: Beglova
mesh_terms: D000818:Animals; D016736:Antiphospholipid Syndrome / Q000097:blood / Q000276:immunology*; D002118:Calcium / Q000378:metabolism; D002308:Cardiolipins / Q000032:analysis / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D026502:LDL-Receptor Related Proteins / Q000235:genetics* / Q000378:metabolism*; D008024:Ligands; D008807:Mice, Inbred BALB C; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D014914:Whole Blood Coagulation Time; D053482:beta 2-Glycoprotein I / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism*
chemical_list: D002308:Cardiolipins; D026502:LDL-Receptor Related Proteins; D008024:Ligands; D011994:Recombinant Proteins; D053482:beta 2-Glycoprotein I; C098773:low density lipoprotein receptor-related protein 8; D002118:Calcium
keywords: ApoER2; ApoH; antiphospholipid syndrome; lipoprotein receptor; β2GPI