beta 2-Glycoprotein-I (apolipoprotein H) interactions with phospholipid vesicles

The binding characteristics of the human serum protein beta 2-glycoprotein-I, also called apolipoprotein H, with multilamellar phospholipid vesicles has been studied. It was found that beta 2-G-I is not or almost not bound to the "neutral" phospholipids phosphatidylcholine (PC), phosphatidylethanolamine (PE) and sphingomyelin (SM). The negatively charged compounds phosphatidylserine (PS) and phosphatidylinositol (PI) interact strongly with beta 2-G-I. In terms of phospholipid concentration the binding to PS is about one order of magnitude greater than to PI. The binding capacity is influenced by several parameters such as the molarity of buffer, presence of mono- or divalent cations as well as ethylenediaminotetraacetic acid (EDTA). Proteins like bovine serum albumin (BSA), human serum albumin (HSA) or horse gamma-globulin (HGG) influence the binding also in a concentration dependent manner.