Quantifying the Heterogeneous Dynamics of a Simulated Dipalmitoylphosphatidylcholine (DPPC) Membrane
Jack F. Douglas, Neha Shafique, Francis W. Starr
Cell membranes, composed primarily of lipid bilayers, are dynamically active structures. While the relationship between heterogeneity of dynamics and biological function is becoming increasingly appreciated, the dynamical characteristics of lipid membranes remain a topic of vigorous debate. Here we examine cooperativity of lipid dynamics via molecular simulations of single-component DPPC lipid bilayers modeled using the MARTINI force field. The single component membrane provides a first step in a systematic, bottom-up approach to establish a quantitative framework for membrane dynamics. We draw upon well-established methods from other strongly-interacting condensed materials to characterize membrane dynamic hetero-geneity. Consistent with experiments, our findings show significant changes in lipid dynamics between the liquid-disordered, liquid-ordered, and gel phases. Similar to the dynamics seen in simple liquids approaching their glass transition, we can dis-tinguish two mobility groups in the ordered phases: (i) lipids that are transiently trapped by their neighbors, and (ii) lipids with relatively large displacements on the scale of the intermolecular spacing. The lipid molecules dynamically exchange between these mobility groups. Most significantly, these distinct mobility groups are spatially segregated and form dynamic clusters. We provide a quantitative description of these dynamic lipid clusters and find that their time (1 µs to 2 µs) and and size (1 nm to 10 nm) scales are comparable to those of many proteins and other biomolecules. Thus, these clusters likely play a part in dynamical organization of membranes. These scales are consistent with those expected for complex raft structures, suggesting that this intrinsic lipid heterogeneity plays an important role in the formation of much debated rafts.
, Shafique, N.
and Starr, F.
Quantifying the Heterogeneous Dynamics of a Simulated Dipalmitoylphosphatidylcholine (DPPC) Membrane, Journal of Physical Chemistry B
(Accessed June 10, 2023)