Abstract
Local structure and dynamics of lipid membranes play an important role in membrane function. The diffusion of small molecules, the curvature of lipids around a protein and the existence of cholesterol-rich lipid domains (rafts) are examples for the membrane to serve as a functional interface. The collective fluctuations of lipid tails, in particular, are relevant for diffusion of membrane constituents and small molecules in and across membranes, and for structure and formation of membrane domains. We studied the effect of aspirin (acetylsalicylic acid, ASA) on local structure and dynamics of membranes composed of dimyristoylphosphocholine (DMPC) and cholesterol. Aspirin is a common analgesic, but is also used in the treatment of cholesterol. Using coherent inelastic neutron scattering experiments and molecular dynamics (MD) simulations, we present evidence that ASA binds to liquid-ordered, raft-like domains and disturbs domain organization and dampens collective fluctuations. By hydrogen-bonding to lipid molecules, ASA forms ‘superfluid’ complexes with lipid molecules that can organize laterally in superlattices and suppress cholesterol’s ordering effect.
Highlights
Membrane research progresses with ever-increasing levels of granularity
Inelastic neutron scattering experiments were performed on oriented DMPC-d54 (1,2dimyristoyl-sn-glycero-3-phosphocholine) bilayers containing cholesterol and ASA
Membranes were prepared by dissolving DMPC, cholesterol and aspirin in a 1 : 1 solution of trifluoroethanol/chloroform, at the appropriate molar ratios, and depositing the solution on 1 × 1 cm2 silicon wafers
Summary
Membrane research progresses with ever-increasing levels of granularity. Initial models of the membrane as an inert, physical barrier were revised with the discovery of membrane-embedded proteins. Singer & Nicholson [1] devised their famous ‘fluid mosaic’ model to describe a system where proteins float in a featureless soup of various lipid types. Membrane research has focused on membrane details on the level of individual lipids and proteins. The lipid environment in the specific region around a protein, such as the hydrophobic.
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