Dynamic Lipid Lateral Segregation Driven by Lauryl Cyclodextrin Interactions at the Membrane Surface

Amphiphilic cyclodextrins, with a cholesterol anchor (beta Chol) or an aspartic acid moiety esterified by two lauryl acyl chains (beta DLC), were designed to combine the inclusion ability of the cyclodextrin cavity with the carrier properties of model membranes. Their insertion in phosphatidylcholine bilayers induces a marked lateral phase separation into a pure lipid phase and a cyclodextrin-rich phase (L-CD), organized as a 2D cyclodextrin network stabilized by intermolecular hydrogen bonds between the saccharide headgroups at the membrane surface (Roux, M.; Perly, B.; Djedaini-Pilard, F. Self-Assemblies of Amphiphilic Cyclodextrins. Eur. Biophys. J. 2007, 36, 861-867). We have replaced the dilauryl anchor by a single lauryl chain grafted onto a leucine residue, giving monolauryl-beta-cyclodextrin (beta MLC), which readily inserts into bilayers of chain-deuterated DMPC-d(27). The removal of one lauryl acyl chain leads to a dynamic membrane insertion of this new cyclodextrin derivative, with significant lipid exchange on the deuterium NMR time scale between a loosely packed cyclodextrin-enriched phase (L'(CD)) and free lipid regions, yielding broadened two-component NMR spectra. Like the LCD phases, the cyclodextrin-enriched L'(CD) regions remain (partially) fluid below the DMPC-d(27) main fluid-to-gel transition but do not undergo a clear transition toward a gel state, as observed at 14.5 degrees C in the L-CD phase induced by the dilauryl derivative. Partially fluid lipids of the beta MLC-induced L'(CD) phase coexist with pure lipids in the P-beta', gel phase with possible exchange between them until all of the lipids undergo a transition toward an L-beta', gel state at around 7 degrees C. Trimethylated monolauryl-beta-cyclodextrins induce only an ordering of the lipid acyl chains just above the main transition, without any lateral phase separation. Similar chain ordering is also observed within the beta MLC-induced L'(CD) phase as a consequence of the deep membrane insertion of the monolauryl nonmethylated cyclodextrin derivative.