Biophysical Properties and Applications of Cholesterol in Lipid Membranes

This series of images illustrates the influence of latex nanoparticles on a phase separated lipid monolayer.  These images were acquired with fluorescence microscope using a novel micro-fluidic flow cell.  In this experiment a 1:1:1 mixture of POPC/Brain SM (sphingomylin)/Cholesterol was deposited at the air water interface.  0.5% Texas Red DPPE was added to the monolayer to provide contrast for fluorescence microscopy.  The nanoparticles were not dyed.  A) An initial series of images was taken of the monolayer on a 1X PBS subphase.  B)  The addition of latex microspheres into the subphase (0.02 micon) steadily increased the monolayer surface pressure.  C) Ultimately resulting in a phase transition.

The plasma cell membrane is a dynamic biological structure which separates the cell from its surroundings, localizes proteins at an interface, and plays an active role in many cellular processes.  The multi-functionality of the membrane is provided by a diverse array of molecules.  For example, in the presence of water, amphiphilic molecules called lipids self-assemble into bilayers which provide a structural backbone for the membrane.  Of these lipids, cholesterol has been identified as unique.  I will describe work in my lab to understand how structural features of the cholesterol molecule confer important biophysical properties to the lipid membrane.  Two areas of focus will be: preliminary measurements of nanoparticles/monolayers interactions and line tension measurements between coexisting liquid phases.  Materials scientists and engineers seek to exploit the biophysical properties of these systems in the development of biomimetic surfaces and drug delivery systems.  Potential applications of this work as a tool in biotechnology, experimental techniques, and future research directions will be described.