Lipid Phase Behavior

Lipid Phase Behavior

Our research in cell membranes considers mechanisms such as: How do lipids partition into ordered and disordered micro-domains when self-assembled into layers? In cell membranes, how does lipid composition (type and ratio) affect interactions with embedded proteins or extracellular agents? We address these questions through computer simulations and experiments with model lipid membranes where the composition and packing of the lipids can be precisely controlled while simultaneously determining their structure, orientation, and dynamic motions.

We combine a variety of techniques to decode these phenomena. For example, a Langmuir-Blodget trough compressing a lipid monolayer at the air-water interface allows the lipids’ thermodynamic environment to be controlled explicitly while fluorescence microscopy simultaneously images the size and shape of domains in the condensed phase.

In addition, we have pioneered what is the first successful application of X-rays in characterizing the structure of supported lipid bilayers at the solid-liquid interface. Through novel environmental and experimental controls, we have been able to adapt two common scattering techniques-X-ray grazing incidence diffraction (GID) and specular reflectivity (XR)-to probe the thickness of soft biological materials with roughly twice the resolution previously accessible with other techniques.

lipid_phase1 Top: The hypothesized segregation of cholesterol (purple) and sphingolipids (orange) into clusters called rafts that are believed to play important roles in modifying the properties of living cells.

Bottom: A Monte Carlo simulation demonstrates how the assault of cholera toxin on a lipid membrane disrupts the packing of lipids into what would otherwise be a highly-ordered crystalline phase.