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Stability, function, renaturation and immobilization of membrane proteins complexed by amphipathic polymers (amphipols)

Nanoscience Seminar by Jean-Luc Popot, CNRS, Paris, France

Abstract
Membrane proteins classically are handled in aqueous solutions as complexes with detergents. The dissociating character of detergents, combined with the need to maintain an excess of them, frequently results in more or less rapid inactivation of the protein under study. Over the past ten years, we have endeavored to develop two novel families of surfactants aiming at circumventing some of the problems encountered with detergents (1,2). One of them comprises short amphiphilic polymers dubbed 'amphipols' (3-5). Because each amphipol molecule carries numerous hydrophobic chains, it binds to the transmembrane surface of integral membrane proteins (6) in a non-covalent but, in the absence of a competing surfactant, quasi-irreversible manner (4,7,8). Membrane proteins complexed by amphipols are in their native state, stable, and they remain water-soluble in the absence of detergent or free amphipols (3,4,8). Amphipols have many potential applications in cellular and structural membrane biology (4), including the renaturation of membrane proteins (9), their immobilization onto solid supports (unpublished), and their study by solu¬tion NMR (6), electron microscopy (10), and, perhaps, X ray crystallography (unpublished). The mechanism(s) by which they stabilize membrane proteins may involve damping of large-scale movements of protein transmembrane regions (9,11).