Structural studies of membrane proteins (MP) in a native or native-like environment remain a challenge. X-ray crystallography of three-dimensional crystals of MP in lipids and cryo-electron microscopy of two-dimensional crystals also in lipids have given atomic structures of several MP. Recent developments of solid-state NMR (ssNMR) provided structural data of MP in lipids and should give access to the dynamic behavior of MP\'s in a native-like environment. Preparation of samples for ssNMR is not trivial with overexpressed proteins since purified recombinant MP have to be reincorporated in proteoliposomes and concentrated in the small volume of the rotor used for ssNMR studies. We present here the protocol that we have used to study the recombinant mouse TSPO1, an integral membrane protein of 20 kDa mostly found in the outer membrane of mitochondria and overexpressed in E. coli bacteria.

The targets of many small molecule drugs are membrane proteins, and traditionally the focus of pharmacology is on the interaction between such receptors and their small molecule drug ligands. However, the lipid membranes of cells and organelles are increasingly appreciated as diverse and dynamic structures that also specifically interact with small molecule drugs and peptides, causing profound changes in the properties of these membranes, and modulating the function of the membrane and the proteins within it. Drug-membrane interactions are likely to have a role in both the therapeutic and toxic activity of a variety of compounds, and their role in the overall pharmacological effect of a drug needs to be understood more clearly. This is the case for the 18 kDa translocator protein (TSPO) and its ligands, where functions that were established based on pharmacological studies are being called into question. Re-examining the putative functions of the TSPO and the effects of its ligands reveals a need to consider in more detail the interplay between protein-ligand and membrane-ligand interactions, and the modulatory relationship between TSPO and the lipid membrane.