Cholesterol solubility limit in lipid membranes probed by small angle neutron scattering and MD simulations

The solubility limits of cholesterol in small unilamellar vesicles made of POPS and POPC were probed using Small Angle Neutron Scattering (SANS) and coarse grained (CG) molecular dynamics (MD) simulations. SANS, being non-invasive, allowed the direct and quantitative measurement of cholesterol in intact vesicles. Our experimental measurements reveal a 61% mole fraction solubility limit of cholesterol in POPC, consistent with previous studies. However, in POPS the solubility limit of cholesterol is found to be 73% mole fraction. Previous work reports solubility limits of cholesterol in POPS varying significantly, ranging from 36% up to 66%. The CG MD simulations are in remarkable quantitative agreement with our experimental results showing similar solubility limits. Further, neither experiments nor simulations show evidence of stable nanodomains of cholesterol in POPS membranes as suggested in some previous reports.