Lipids in Motion: Understanding the Energy Landscape of Lipids in Cell Membranes

Lipids are amphiphilic molecules that love and hate water simultaneously and self-assemble into a lipid bilayer that is a universal structure of all cell membranes. The membrane’s hydrophobic interior is a 4nm-thick film that separates the interior of the cells from the surrounding environment. Structures inside the cell, such as the nucleus, evolved to be bounded by membranes in eukaryote cells; in fact, it is the hallmark that sets them apart from prokaryotic cells. Hence, biological membranes are not only life/death boundaries for cells but are also necessary for the existence of higher organisms like us. However, the mere function of a “confining barrier” does not explain why eukaryotic cells invest substantial resources in generating thousands of different lipids (~5% of their genes!) to form membranes. Indeed, the lipid composition of individual membranes within a cell varies significantly. Consider the case of cholesterol: the endoplasmic reticulum, where it is synthesized, contains barely 1% of the total cell cholesterol, while the plasma membrane contains about 40%. So the question arises: how do cells create these unique compositions and multiple functionalities in their individual membranes? The answer to this question is explained in part by thermally-driven properties of lipids in and between membranes. In this talk, Perez-Salas will present results from ongoing efforts to map the energy landscape of lipid motion between distinct membranes and within a single membrane. These recent efforts concentrate primarily on neutron scattering techniques that, she will argue, are highly desirable because other probing techniques potentially can be too invasive, resulting in skewed results.