Influence of Hydrophobic Groups Attached to Amphipathic Polymers on the Solubilization of Membrane Proteins along with Their Lipids

Abstract

One of the biggest challenges in membrane protein (MP) research is to secure physiologically relevant structural and functional information after extracting MPs from their native membrane. Amphipathic polymers represent attractive alternatives to detergents for stabilizing MPs in aqueous solutions. The predominant polymers used in MP biochemistry and biophysics are amphipols (APols), one class of which, styrene maleic acid (SMA) copolymers and their derivatives, has proven particularly efficient at MP extraction. In order to examine the relationship between the chemical structure of the polymers and their ability to extract MPs from membranes, we have developed two novel classes of APols bearing either cycloalkane or aryl (aromatic) rings, named CyclAPols and ArylAPols, respectively. The effect on solubilization of such parameters as the density of hydrophobic groups, the number of carbon atoms and their arrangement in the hydrophobic moieties, as well as the charge density of the polymers was evaluated. The membrane-solubilizing efficiency of the SMAs, CyclAPols, and ArylAPols was compared using as models (i) two MPs, BmrA and a GFP-fused version of LacY, overexpressed in the inner membrane of Escherichia coli, and (ii) bacteriorhodopsin, naturally expressed in the purple membrane of Halobacterium salinarum. This analysis shows that, as compared to SMAs, the novel APols feature an improved efficiency at extracting MPs while preserving native protein–lipid interactions.

Synthesis of well‐defined methacrylate copolymers and their use for stabilizing membrane proteins

“…Despite the presence of a cyclic hydrophobic moiety, the copolymers extracted much smaller amounts of BmrA compared with SMA and CyclAPols. 21 Moreover, an increase from 33 to 50% of CHMA did not show a significant improvement of the extraction rate, and a change of the PEG length did not impact the properties either. We first hypothesized that a higher ratio of CHMA in the copolymer would improve the extraction.…”

“…Recently, based on the hypothesis that cyclic hydrophobic moieties in amphiphilic copolymers are effective extracting agents for membrane proteins, a novel type of amphipol containing cyclic aliphatic groups instead of linear chains, called CyclAPols (Figure 1), was developed by Marconnet et al 20,21 Various cycloalkane amphipols were designed by varying the number of carbon atoms in the side groups to tune hydrophobicity. CyclAPols were tested on the bacteriorhodopsin from Hb.…”