Multicomponent bilayers
Participating group members:  Hao Wang, Fuchang Yin, Patrick Coppock,
Jennifer Colucci

Biological membranes contain dozens of different types of lipid, a mixture that is specific to the type of cell and membrane and is tightly regulated by the cell's metabolic machinery.  In learning about the physical properties of mixed bilayers through computer simulation, we hope to better understand why this lipid diversity is so important.  We use both atomistic methods and highly simplified models.  The snapshot below is from a Monte Carlo simulation in which two different lengths of lipid are modeled as simple hard rods, and the degree of mixing is studied. For more on this model (which was a research project for two undergraduate students), see here.

More information can be obtained using molecular models with more realistic representations of molecular structure and interactions. However, atomistic simulations of lipid mixtures are challenging because lipid lateral diffusion is slow on the practical timescale for computer simulation, which is generally limited to 10's of nanoseconds for these detailed models. Lipids pretty much stay wherever they start out for the whole simulation, so it is difficult to learn whether they have a tendency to form clusters or to migrate to different membrane strutures like transmembrane proteins. Postdoctoral fellow Jason de Joannis has developed and implemented a method to incorporates "mutation" moves into a simulation, thereby allowing the development of an equilibrium distribution of lipids orders of magnitude faster than through conventional dynamics simulation.


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