Solubilization and Stabilization of Membrane Proteins by Cycloalkane-Modified Amphiphilic Polymers

Abstract

Membrane proteins need to be extracted from biological membranes and purified in their native state for most structural and functional in vitro investigations. Amphiphilic copolymers, such as amphipols (APols), have emerged as very useful alternatives to detergents for keeping membrane proteins water-soluble under their native form. However, classical APols, i.e. poly(acrylic acid) (PAA) derivatives, seldom enable direct membrane protein extraction. Poly(styrene-maleic anhydride) copolymers (SMAs), which bear aromatic rings as hydrophobic side groups, have been reported to be more effective extracting agents. In order to test the hypothesis of a role of cyclic hydrophobic moieties in membrane solubilization by copolymers, we have prepared PAA derivatives comprising cyclic rather than linear aliphatic side groups (CyclAPols). As references, APol A8-35, SMAs, and diisobutylene maleic acid (DIBMA) were compared with CyclAPols. Using as models the plasma membrane of Escherichia coli and the extraction-resistant purple membrane from Halobacterium salinarum, we show that CyclAPols combine the extraction efficiency of SMAs with the stabilization afforded to membrane proteins by classical APols such as A8 35.