Influence of Domain Size on Structure and Elastic Fluctuations in Complex Lipid Mixtures

Abstract

Lipid-only domains are well-established mimetic systems for membrane rafts enabling the study of their physical properties under strictly controlled conditions. Of particular interest are four component lipid mixtures entailing the variation of lipid domain size from micron regime down to a few nanometers [1]. Applying our recently developed small-angle x-ray scattering data analysis technique, we have studied changes of membrane thickness, lateral lipid packing and bending fluctuations for coexisting liquid-ordered (Lo) and liquid-disordered (Ld) phases in DOPC/POPC/DSPC/cholesterol mixtures along this domain-size trajectory, including the melting of Lo domains as a function of temperature. Bending fluctuations for coexisting Lo domains were found to be significantly lower than for single Lo phases at the boundary of the Lo+Ld regime. In turn, little variation was observed when domains exceeded sizes of 160 nm. Further, we found that the melting of Lo domains as a function of temperature is controlled by thickness differences between Lo and Ld and the associated domain line tension.This work was supported by Austrian Science Fund FWF, Project No. P24459-B20.[1] F.A. Heberle et al., J. Am. Chem. Soc. 135 (18), 6853-6859 (2013)