How to Catch a Membrane Protein in Action: A Review of Functional Membrane Protein Immobilization Strategies and Their Applications

Functional immobilization of membrane proteins (MP) requires consideration of their physiological needs, often dictated by the quality and components of the natural hydrophobic environment surrounding this class of proteins. With MPs, often the challenge is not the immobilization per se, but rather the requirements of the analysis and the protein itself with regards to protein availability and the type of lipid environment needed. The most successful stories are currently based on the nicotinic acetylcholine receptor and rhodopsin, due to the availability of these MPs in large quantities and relatively good stabilities. As opposed to soluble proteins, MP interactions with ligands, lipids, or other proteins are often specifically located on one side of the cellular membrane. Competition binding studies using known, fluorescent ligands confirmed the functionality of the proteins studied. In comparison to wholecell analyses, the advantages of supported cell-membrane sheets are numerous.