Membrane proteins play a pivotal role in all branches of life. They are the cell’s gatekeeper, deciding which molecules or proteins can pass. They are not only located within the cell membrane, but also within every other compartment-separating membrane, for example mitochondria or nucleus.
Two folds dominate current membrane protein biology. There are transmembrane helices, piercing the membrane from one end to the other end. Usually several helices assemble, for example provided by several (different) proteins, to establish a fully functional membrane protein of this sort. The second folding are beta-barrel membrane proteins. These proteins have a beta-sheet secondary structure which folds as a barrel and allows hydrophilic molecues to pass the hydrophobic membrane barrier.
It is, however, difficult for biophysical methods such as NMR, cryo-EM or x-ray, to study membrane proteins since a hydrophobic environment is required for their proper function. We use so called nanodiscs. They provide a lipid bilayer patch in which a membrane protein can be immersed and studied in its natural environment. OmpX (outer membrane protein X) is one example for a beta-barrels membrane protein we study in micelles, bicelles and nanodiscs to understand its dynamic behavior. Further membrane proteins are the KcsA potassium channel and YgaP.