Membrane proteins, which make up around one third of the proteome, perform a wide variety of biological functions and are important drug targets, but crystallisation and structural and functional analysis have so far proved challenging. A study published in the journal PNAS which describes the use of amphipathic polymers (“amphipols”) to replace the lipid membrane may provide a generalised method of stabilising and immobilising membrane proteins in their native state. The amphipol can be used to attach the functional protein to almost any type of solid support, including chips and beads. Amphipols are short soluble polymers with many hydrophobic side chains by means of which they are able to associate with the transmembrane domain of proteins, thereby maintaining water solubility without the use of detergents. Although non-covalent, the association is irreversible unless another surfactant is added.
The authors suggest that amphipol-mediated immobilisation of membrane proteins represents a significant improvement over existing methodologies and demonstrated the generality of the approach by immobilising proteins from several different sources onto supports suitable for either label-free or fluorescence-based ligand binding studies. Although the possibility of amphipol interference with ligand binding cannot be completely ruled out, it is seen as unlikely to be a serious problem in most cases.