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FOR THE RECORD

Stabilization of membranes upon interaction of amphipathic polymers with membrane proteins

¹ Unité de Recherche Associée 2096 (Centre National de la Recherche Scientifique et Commissariat à l’Energie Atomique) & Section de Biophysique des Fonctions Membranaires, Département de Biologie Joliot-Curie, CEA Saclay, 91191 Gif-sur-Yvette cedex, France, and Laboratoire de Recherche Associé 17V & Institut Fédératif de Recherches 46, Université Paris Sud, France
² Unité Mixte de Recherche 6522 (Centre National de la Recherche Scientifique), Université de Rouen, 76821 Mont-Saint-Aignan cedex, France

(RECEIVED July 1, 2004; FINAL REVISION July 1, 2004; ACCEPTED July 26, 2004)

Amphipathic polymers derived from polysaccharides, namely hydrophobically modified pullulans, were previously suggested to be useful as polymeric substitutes of ordinary surfactants for efficient and structure-conserving solubilization of membrane proteins, and one such polymer, 18C₁₀, was optimized for solubilization of proteins derived from bacterial outer membranes (Duval-Terrié et al. 2003). We asked whether a similar ability to solubilize proteins could also be demonstrated in eukaryotic membranes, namely sarcoplasmic reticulum (SR) fragments, the major protein of which is SERCA1a, an integral membrane protein with Ca²⁺-dependent ATPase and Ca²⁺-pumping activity. We found that 18C₁₀-mediated solubilization of these SR membranes did not occur. Simultaneously, however, we found that low amounts of this hydrophobically modified pullulan were very efficient at preventing long-term aggregation of these SR membranes. This presumably occurred because the negatively charged polymer coated the membranous vesicles with a hydrophilic corona (a property shared by many other amphipathic polymers), and thus minimized their flocculation. Reminiscent of the old Arabic gum, which stabilizes Indian ink by coating charcoal particles, the newly designed amphipathic polymers might therefore unintentionally prove useful also for stabilization of membrane suspensions.

Keywords: membrane protein; solubilization; amphiphilic polysaccharide; pullulan; sarcoplasmic reticulum; corona

Abbreviations: SR, sarcoplasmic reticulum • ATPase, adenosine triphosphatase • 18C₁₀, hydrophobically modified carboxymethylpullulan (see Duval-Terrié et al. 2003) • A8–35, hydrophobically modified polyacrylic acid in its sodium form (see Tribet et al. 1996) • TES, N-tris[hydroxymethyl]-methyl-2aminoethane-sulfonic acid

Reprint requests to: Martin Picard, Unité de Recherche Associée 2096 (Centre National de la Recherche Scientifique et Commissariat à l’Energie Atomique) & Section de Biophysique des Fonctions Membranaires, Dé-partement de Biologie Joliot-Curie, CEA Saclay, 91191 Gif-Sur-Yvette cedex, France; e-mail:picard{at}dsvidf.cea.fr; fax: +33-1-6908-8139.

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