Amphipols are a new class of surfactants that make it possible to handle membrane proteins in detergent-free aqueous solution as though they were soluble proteins. The strongly hydrophilic backbone of these polymers is grafted with hydrophobic chains, making them amphiphilic. Amphipols are able to stabilize in aqueous solution under their native state four well-characterized integral membrane proteins: ( i ) bacteriorhodopsin, ( ii ) a bacterial photosynthetic reaction center, ( iii ) cytochrome b ₆ f , and ( iv ) matrix porin.

Amphipols (APols) are short amphipathic polymers that can substitute for detergents to keep integral membrane proteins (MPs) water soluble. In this review, we discuss their structure and solution behavior; the way they associate with MPs; and the structure, dynamics, and solution properties of the resulting complexes. All MPs tested to date form water-soluble complexes with APols, and their biochemical stability is in general greatly improved compared with MPs in detergent solutions. The functionality and ligand-binding properties of APol-trapped MPs are reviewed, and the mechanisms by which APols stabilize MPs are discussed. Applications of APols include MP folding and cell-free synthesis, structural studies by NMR, electron microscopy and X-ray diffraction, APol-mediated immobilization of MPs onto solid supports, proteomics, delivery of MPs to preexisting membranes, and vaccine formulation.

We study the adsorption dynamics of an azobenzene-based photo-responsive charged surfactant to investigate how photo-stimulation impacts the dynamics at an air–water interface. The hydrophobic tail of this photo-responsive surfactant photo-converts reversibly from a cis to a trans conformation when the wavelength switches from UV to blue. This change in conformation results in a decrease of the surface tension. Using a kinetically limited model of adsorption, including the electrostatics effects and the competition between the two photo-isomers, we reproduce the dynamics of adsorption of AzoTAB measured experimentally. We find that the cis isomer adsorbs 10 times faster than the trans isomer but the cis conformation also desorbs 300 times faster. As a result, within a few seconds a non-stimulated interface becomes composed of almost 100% trans isomers. We then focus on the competition between the photo-conversion and the adsorption at the interface. Indeed when the interface is stimulated, part of the adsorbed trans isomers rapidly convert to cis. As the latter quickly desorbs, the surface coverage decreases: the light induces a “pumping-out” of the interface. The photo-stimulated interface reaches a stationary state where a vertical gradient of composition is established below the surface. Finally, this study highlights a new way to stimulate a photo-responsive interface: for a solution prepared under blue light, instead of photo-converting the bulk composition by stimulating under UV (which can be quite slow for high absorbance solutions), one can tune and reach a stabilized value of the surface tension in few seconds by stimulating the interface with a blue light with high enough intensity.

This review summarizes recent investigations on the association of macromolecules on lipid bilayers. Hydrophilic and flexible polymers can form soft coronae tenuously adsorbed or anchored on the lipid membrane. Other synthetic macromolecules are embedded in the apolar region of the membrane. Recent experimental and theoretical works focus on the perturbation of lipid properties achieved depending on the nature and strength of binding. Of importance to biomimicry, to tethered model membranes, and drug carriers, the effects achievable include modulation of the lateral diffusivity of lipids, shape distortions, lateral segregations, formation of well-defined nanopores and ultimately the stimuli responsive disruption of the membrane.