Monolayer spontaneous curvature of raft-forming membrane lipids

Monolayer spontaneous curvatures for cholesterol, DOPE, POPE, DOPC, DPPC, DSPC, POPC, SOPC, and egg sphingomyelin were obtained using small-angle X-ray scattering (SAXS) on inverted hexagonal phases (H_II). Spontaneous curvatures of bilayer forming lipids were estimated by adding controlled amounts to a H_II forming template following previously established protocols. Spontaneous curvatures of both phosphatidylethanolamines and cholesterol were found to be at least a factor of two more negative than those of phosphatidylcholines, whose J₀ values are closer to zero. Interestingly, a significant positive J₀ value was retrieved for DPPC. We further determined the temperature dependence of the spontaneous curvatures J₀(T) in the range from 15 to 55 °C, resulting in a quite narrow distribution of -1 to -3 × 10^-3 (nm °C)^-1 for most investigated lipids. The data allowed us to estimate the monolayer spontaneous curvatures of ternary lipid mixtures showing liquid ordered/liquid disordered phase coexistence. We report spontaneous curvature phase diagrams for DSPC/DOPC/Chol, DPPC/DOPC/Chol and SM/POPC/Chol and discuss effects on protein insertion and line tension.