Folding alpha-helical membrane proteins into liposomes in vitro and determination of secondary structure

The native environment of integral membrane proteins is a highly complex lipid bilayer composed of many different types of lipids, the physical characteristics of which can profoundly influence protein stability, folding, and function. Secondary transporters are a class of protein where changes to both structure and activity have been observed in different bilayer environments. In order to study these interactions in vitro, it is necessary to extract and purify the protein and exchange it into an artificial lipid system that can be manipulated to control protein behavior. Liposomes are a commonly used model system that is particularly suitable for studying transporters. GalP and LacY can be reconstituted or refolded into vesicles with a high degree of efficiency for further structural analysis. Circular dichroism spectroscopy is an important technique in monitoring protein folding, which allows the decomposition of spectra into secondary structural components.