Micron-scale phase segregation in lipid monolayers induced by myelin basic protein in the presence of a cholesterol analog

It was previously shown that myelin basic protein (MBP) can induce phase segregation in whole myelin monolayers and myelin lipid films, which leads to the accumulation of proteins into a separate phase, segregated from a cholesterol-enriched lipid phase. In this work we investigated some factors regulating the phase segregation induced by MBP using fluorescent microscopy of monolayers formed with binary and ternary lipid mixtures of dihydrocholesterol (a less-oxidable cholesterol analog) and phospholipids. The influence of the addition of salts to the subphase and of varying the lipid composition was analyzed. Our results show that MBP can induce a dihydrocholesterol-dependent segregation of phases that can be further regulated by the electrolyte concentration in the subphase and the composition (type and proportion) of non-sterol lipids. In this way, changes of the lipid composition of the film or the ionic strength in the aqueous media modify the local surface density of MBP and the properties (phase state and composition) of the protein environment. (C) 2009 Elsevier B.V. All rights reserved.