Effects of cholesterol and PIP2 on interactions between glycophorin A and Band 3 in lipid bilayers.

In the erythrocyte membrane, the interactions between glycophorin A (GPA) and Band 3 are associated strongly with the biological function of the membrane and several blood disorders. In this work, using coarse-grained molecular-dynamics simulations, we systematically investigate the effects of cholesterol and phosphatidylinositol-4,5-bisphosphate (PIP2) on the interactions of GPA with Band 3 in the model erythrocyte membranes. We examine the dynamics of the interactions of GPA with Band 3 in different lipid bilayers on the microsecond time scale and calculate the binding free energy between GPA and Band 3. The results indicate that cholesterols thermodynamically favor the binding of GPA to Band 3 by increasing the thickness of the lipid bilayer and by producing an effective attraction between the proteins due to the depletion effect. Cholesterols also slow the kinetics of the binding of GPA to Band 3 by reducing the lateral mobility of the lipids and proteins and may influence the binding sites between the proteins. The anionic PIP2 lipids prefer binding to the surface of the proteins through electrostatic attraction between the PIP2 headgroup and the positively charged residues on the protein surface. Ions in the solvent facilitate PIP2 aggregation, which promotes the binding of GPA to Band 3.