Monolayer Spontaneous Curvature of Raft-Forming Membrane Lipids

TL;DR

This study measures the spontaneous curvature of various membrane lipids using SAXS, revealing differences among lipid types and their temperature dependence, and provides phase diagrams for lipid mixtures affecting membrane properties.

Contribution

It introduces a method to quantify monolayer spontaneous curvature of lipids and lipid mixtures, expanding understanding of membrane biophysics.

Findings

Phosphatidylethanolamines and cholesterol have more negative J0 than phosphatidylcholines.

DPPC exhibits a positive J0 at 25°C.

Spontaneous curvature varies narrowly with temperature from -1 to -3 * 10^-3 1/nm/°C.

Abstract

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 (HII). Spontaneous curvatures of bilayer forming lipids were estimated by adding controlled amounts to a HII forming template following previously established protocols. Spontanous curvatures of both phosphatidylethanolamines and cholesterol were found to be at least a factor of two more negative than those of phosphatidylcholines, whose J0 are closer to zero. Interestingly, a significant positive J0 value (+0.1 1/nm) was retrieved for DPPC at 25 {\deg}C. We further determined the temperature dependence of the spontaneous curvatures J0(T) in the range from 15 to 55 \degC, resulting in a quite narrow distribution of -1 to -3 * 10^-3 1/nm{\deg}C 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.