Biophys J, June 2001, p. 2898-2911, Vol. 80, No. 6

Detergents as Probes of Hydrophobic Binding Cavities in Serum Albumin and Other Water-Soluble Proteins

Ulrich Kragh-Hansen,^* Florence Hellec, Béatrice de Foresta, Marc le Maire, and Jesper V. Møller

Departments of  ^*Medical Biochemistry and  Biophysics, University of Aarhus, DK-8000 Aarhus C, Denmark; and  Section de Biophysique des Protéines et des Membranes, Département de Biologie Cellulaire et Moléculaire, CEA, CNRS-URA 2096 et Université Paris Sud-LRA 17V, Centre d'Etudes de Saclay, F-91191 Gif-sur-Yvette, Cedex, France

As an extension of our studies on the interaction of detergents with membranes and membrane proteins, we have investigated their binding to water-soluble proteins. Anionic aliphatic compounds (dodecanoate and dodecylsulfate) were bound to serum albumin with high affinity at nine sites; related nonionic detergents (C₁₂E₈ and dodecylmaltoside) were bound at seven to eight sites, many in common with those of dodecanoate. The compounds were also bound in the hydrophobic cavity of -lactoglobulin, but not to ovalbumin. In addition to the generally recognized role of the Sudlow binding region II of serum albumin (localized at the IIIA subdomain) in fatty acid binding, quenching of the fluorescence intensity of tryptophan-214 by 7,8-dibromododecylmaltoside and 12-bromododecanoate also implicate the Sudlow binding region I (subdomain IIA) as a locus for binding of aliphatic compounds. Our data document the usefulness of dodecyl amphipathic compounds as probes of hydrophobic cavities in water-soluble proteins. In conjunction with recent x-ray diffraction analyses of fatty acid binding as the starting point we propose a new symmetrical binding model for the location of nine high-affinity sites on serum albumin for aliphatic compounds.

Biophys J, June 2001, p. 2898-2911, Vol. 80, No. 6
© 2001 by the Biophysical Society   0006-3495/01/06/2898/14  $2.00