Liquid monolayers. Dynamical lateral order in binary lipid alloys and its coupling to membrane functions

Abstract

This contribution deals with the relation between the dynamical lateral order in model membranes composed of lipid mixtures, and its influence on the function of an integral model protein, the ion-channel gramicidin. Firstly, densitometric and small angle neutron scattering experiments are described for binary alloys organized as liposomal dispersions. These results establish some basic concepts for the understanding of the phase behavior, mixing properties and critical lateral compositional fluctuations in these quasi two-dimensional fluid systems. Next it is shown how the current fluctuations across a bimolecular lipid layer observed when two monomeric gramicidin molecules dimerize within the membrane thus forming an ion-conducting channel can be analyzed to give information about the lateral organization of the lipid matrix. It is shown that phase separation and critical fluctuation, indeed, control the performance parameters of a membrane-integral functional unit.