Capillary electrophoresis-based analysis of phospholipid and glycosaminoglycan binding by human β2-glycoprotein I

Human β2-glycoprotein I (β2gpI) is a phospholipid and heparin binding plasma glycoprotein involved in autoimmune diseases characterized by blood clotting disturbances (thrombosis) together with the occurrence of autoantibodies against β2gpI. With the final goal of assessing autoantibody influence on binding interactions of β2gpI we have studied the development of capillary electrophoresis (CE)-based assays for interactions of negatively charged ligands with β2gpI. In the development of suitable conditions for analysis at neutral pH of this basic protein (pI about 8) we found the pH hysteresis behavior of fused silica surfaces useful since the protonated surface after an acid pre-wash counteracted protein adsorption efficiently in contrast to more laborious procedures including acrylamide/dimethylacrylamide coatings that did not permit analysis of this particular protein. This simple approach made estimates of heparin–β2gpI interactions possible and the principle was shown also to work for detection of β2gpI binding to anionic phospholipids. Utilizing the pH hysteresis effect may be a simple solution to the adsorption problems often encountered in analyses of proteins by CE.