(256j) Self-Assembly of Quorum Sensing Signal Molecules

Quorum sensing (QS) signal molecules are produced by communities of bacteria to coordinate group behavior. N-acyl homoserine lactones (HSLs) are widely characterized amphiphilic QS signal molecules that possess a polar homoserine lactone head group and a nonpolar aliphatic tail. In this work, we investigate the self-assembly of eleven HSLs, most of which are naturally occurring, with two different head groups and varying acyl chain length in aqueous solution. We employed multiscale Molecular Dynamics (MD) simulations to predict the impact of head group structure and tail length on the thermodynamically preferred aggregate structures formed by these HSLs. The results of alchemical free energy calculations using atomistic MD simulations indicate that HSLs containing 10 or more tail carbon atoms form nanoscale aggregates, with C14-HSL, C16-HSL, 3-oxo-C14-HSL, and 3-oxo-C16-HSL preferring to form extended bilayer structures. We also used a suite of biophysical characterization techniques, including light scattering, surface tensiometry, and fluorescence-based assays to measure critical aggregation concentrations (CACs) that are in good agreement with the simulation predictions. We further used transmission electron microscopy (TEM) to visualize the HSL aggregate morphologies to validate the simulation predictions. Finally we used coarse-grained MD simulations to study interactions of HSLs with lipid bilayers to determine the impact of HSL assembly on interactions with other amphiphilic structures. Overall, our results provide insight into processes of self-assembly that occur in this important class of non-ionic amphiphiles, and provide a basis for understanding how HSL chemical structures influence the morphology of self-assembled HSLs. The observation that HSLs can assemble into nanoscale aggregates and associate with other soft material structures (e.g., lipid membranes), also suggests that new synthetic materials could be designed using co-assembly of HSLs.