Advances in the application of fluorescence correlation spectroscopy to study detergent purified and encapsulated membrane proteins

Fluorescence correlation spectroscopy (FCS) is a quantitative spectroscopy technique which could potentially increase throughput and sensitivity of screening for ligand, substrate and inhibitor binding to membrane proteins in solution. However, the purification of membrane proteins in their active forms is complex, as the lipid bilayer provides stability and its removal often causes the protein to become conformationally unstable. This has limited the application of biophysical techniques such as FCS to study the function of membrane proteins. The recent application of native extraction techniques such as styrene maleic acid lipid particles (SMALPs) has resolved this issue and FCS has emerged as a powerful option for studying proteins extracted in this way. This review will discuss the application of FCS to study purified membrane proteins in detergent micelles, nanodiscs and SMALPs and its potential to be used routinely in membrane protein drug discovery.