Lipid bilayers are one of the key components in the cell membrane. The phase behavior of lipids is complex, with even a single component bilayer able to occupy a range of liquid crystalline states. The gel and fluid phases of lipid bilayers are planar and conformationally homogeneous, but the ripple phase, which exists at temperatures between the gel and fluid phases, undulates in an asymmetric sawtooth pattern and consists of heterogeneous conformational clusters.

The cover image of the January 17 issue of Biophysical Journal is a rendering from the molecular dynamics data of a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer in two different phase states, the fluid phase and the ripple phase, along with examples in the middle of the complex conformations that the lipids undertake in the ripple phase: disordered (yellow), disordered and splayed (red), ordered and splayed (green), and ordered (blue). Two of the components, the disordered and ordered lipids, are the homogeneous component of the fluid and gel phases, respectively.

The pictures were generated by using molecular dynamics simulation data of a DPPC lipid bilayer above and below its main phase transition temperature. The rendering was done by using Blender and the Molecular Nodes add-on, which uses the python library MDAnalysis to load real simulation data from a molecular dynamics simulation trajectory.

A deeper understanding at the atomistic scale of the complex conformational behavior of lipids and lipid bilayers could be key to understanding the interactions of molecules, both beneficial and harmful, with the cell membrane.

The workflow developed in our work is not just limited to lipids, and we foresee it being useful in all areas of computational soft matter physics, in particular, polymers and proteins, for which complex molecular conformations need to be identified.

— Matthew Davies, A. D. Reyes-Figueroa, Andrey A. Gurtovenko, Daniel Frankel, and Mikko Karttunen