Liposome Solubilization and Membrane Protein Reconstitution Using Chaps and Chapso

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Abstract
The processes of liposome solubilization and reconstitution of two transport proteins have been studied using Chaps and Chapso (3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-l-propanesulfonate). The solubilization of unilamellar liposomes was followed by absorption experiments and the process was shown to fit well to the three-stage model previously proposed for other detergents. The solubilization parameters have been determined and the detergent to phospholipid ratios at which the lamellar-to-micellar transition initiates and ends were estimated to be 0.21 mol/mol and 0.74 mol/mol, for Chapso and 0.4 mol/mol and 1.04 molhol for Chaps, respectively. The best conditions for the incorporation of two membrane proteins, bacteriorhodopsin and the H+-ATP synthase from chloroplasts, were analyzed at each step of the solubilization process. After detergent removal, the activities of the resulting proteoliposomes were measured indicating that the most efficient reconstitutions were obtained by addition of the proteins to completely solubilized lipid-detergent micelles. The use of Chapso and Chaps for membrane protein reconstitution studies provides a reproducible method of achieving active proteoliposomes, homogeneous in size with a low permeability and thus, well suited for transport measurements.