Lewen Yang successfully defended his thesis, “Line tension assisted membrane permeation at the transition temperature in mixed phase lipid bilayers” in Fall 2017. Lewen’s thesis committed was led by James T. Kindt with Joel Bowman and Michael C. Heaven as additional members.
During his time at Emory, Lewen worked on explaining a phenomenon that was first observed in the early 1970’s, that ions can move more quickly through lipid bilayers when the temperature is close to the bilayer’s melting point. At that temperature, zones of ordered lipids, which are very hard to pass through, exist next to zones of disordered lipids. The experiments suggest that the presence of the ordered lipids make the disordered lipids even more permeable than they would be on their own. The explanation proposed originally, and widely cited still, is that the boundary between these zones is exceptionally leaky. Lewen performed simulations on a highly simplified model that pointed to a different explanation – that leakage doesn’t actually occur at the interfaces themselves, but rather that the line tension of the interface exerts a tension on the disordered lipids that makes them more permeable. He followed up this study with demonstrations, using a more realistic model, that the effect of the interface on the energy barrier to permeation could be predicted quantitatively. His work has opened up a whole new perspective on an interesting phenomenon that is relevant to efforts to use thermally activated lipid containers for targeted drug release.
Lewen started a postdoctoral fellowship at the University of Delaware with Prof. Ed Lyman in April, where he continues to use molecular simulation to understand lipid phase behavior.