Periodic bilayer organization in the complexes of Beta-2 Glycoprotein I with anionic lipid membranes

beta 2 glycoprotein I (beta 2GPI) is a soluble protein that participates in blood coagulation, clearance of apoptotic bodies and generation of antigens in antiphospholipid syndrome among many other functions. We studied the aggregates formed by beta 2GPI with the anionic phospholipids palmitoyloleoylphosphatidyl glycerol, dimyristoylphosphatidyl glycerol, dipalmitoylphosphatidyl glycerol and cardiolipin using small angle X-ray scattering. The complexes obtained in a medium containing 0.01 M NaCl showed Bragg peaks up to the sixth order in a well-defined integer sequence indicating the presence of a lamellar stacking with a periodicity of 17.8 nm and with largely reduced membrane fluctuations. Modeling the complex signal allowed us to conclude that the coherence length was only two bilayers and that about 15% of the total surface was actually stacked. The space between bilayers allows accommodating an extended beta 2GPI molecule making a bridge between the interacting bilayers. The interactions between membranes mediated by beta 2GPI was favored when the membranes were in the liquid crystalline state.

Automated summary

The study found that when beta 2GPI binds with anionic phospholipids, it forms a lamellar stacking with a periodicity, and the interactions between membranes mediated by beta 2GPI are favored when the membranes are in the liquid crystalline state.