Penetration of human apolipoprotein H into air/water interface with and without phospholipid monolayers

Apolipoprotein H (β2-glycoprotein I) is a 54 kDa plasma glycoprotein. The interaction of ApoH with phospholipids has been demonstrated to be involved in the regulation of the function of the activated platelets and the clearance of phosphotidylserine (PS)-expressing cells. In the present work, the monolayer technique is employed to characterize the feature of the penetration of ApoH into air/water interface with and without phospholipid monolayers. The results indicate that ApoH can penetrate into the air/water interface and there is a protein-concentration dependent lag time in the adsorption isotherm. ApoH can insert into the phospholipid monolayers spread at the air/water interface, but no lag time is observed in this case. The fact that ApoH prefers to interact with anionic phospholipid monolayers suggests that the negative charges of the phospholipid monolayers may play an important role in the process of the membrane insertion of ApoH.