Residues in the crystal structure of β₂-GPI that are involved in the interaction with ligands. Domain I contains 2 primary antibody binding sites (highlighted in yellow): the region around Lys19 and the region spanning Arg39 to Arg43. Mutation of residues Asp8 and Asp9 (highlighted in red) enhances the binding of antiphospholipid antibodies to domain I. Domain V contains the phospholipid binding site, which overlaps with the site that interacts with LA1 of LRP8 (highlighted in green).¹¹⁰