Stabilization of integral membrane proteins in aqueous solution using fluorinated surfactants

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Surfactants carrying either a hydrocarbon or a fluorocarbon alkyl chain have been synthesized. The polar head was either tris(hydroxymethyl)acrylamidomethane (THAM), telomerized THAM, or a glycosylated THAM moiety. The aqueous solubility of some of these molecules was increased by oxidizing to a sulfoxide the thioether function that associates their hydrophobic and hydrophilic moieties. In all cases, the critical micellar concentration was principally determined by the length and chemical nature of the alkyl chain. The usefulness of these surfactants in handling integral membrane proteins in solution has been examined using as test materials chloroplast thylakoid membranes and the photosynthetic complex cytochrome b 6 f. In keeping with earlier observations in other systems, none of the fluorinated surfactants was able to solubilize thylakoid membranes. Transfer to a solution of fluorinated surfactant of b 6 f complexes that had been solubilized and purified in the presence of a classical detergent usually resulted in aggregation and precipitation of the protein, while most homologous molecules with hydrocarbon chains did keep the b 6 f complex soluble. Two of the fluorinated surfactants, however, proved able to maintain the b 6 f complex water-soluble, intact, and enzymatically active. Because of their limited affinity for lipid alkyl chains and other hydrocarbon surfaces, fluorinated surfactants appear as potentially interesting tools for the study of membrane proteins that do not stand well exposure to classical detergents.