Amphiphilic biopolymers (amphibiopols) as new surfactants for membrane protein solubilization

The aim of this study was to develop new surfactants for membrane protein solubilization, from a natural, biodegradable polymer: the polysaccharide pullulan. A set of amphiphilic pullulans (HMCMPs), differing in hydrophobic modification ratio, charge ratio, and the nature of the hydrophobic chains introduced, were synthesized and tested in solubilization experiments with outer membranes of Pseudomonas fluorescens. The membrane proteins were precipitated, and then resolubilized with various HMCMPs. The decyl alkyl chain (C-10) was the hydrophobic graft that gave the highest level of solubilization. Decyl alkyl chain-bearing HMCMPs were also able to extract integral membrane proteins from their lipid environment. The best results were obtained with an amphiphilic pullulan bearing 18% decyl groups (18C(10)). Circular dichroism spectroscopy and membrane reconstitution experiments were used to test the structural and functional integrity of 18C(10)-solubilized proteins (OmpF from Escherichia coli and bacteriorhodopsin from Halobacterium halobium). Whatever their structure type (alpha or beta), 18C(10) did not alter either the structure or the function of the proteins analyzed. Thus, HMCMPs appear to constitute a promising new class of polymeric surfactants for membrane protein studies.