Advances in NMR structures of integral membrane proteins

• Solution NMR studies of polytopic integral membrane proteins.
• Fast structure determination of mammalian integral membrane proteins.
• Cell-free synthesis and combinatorial labeling accelerate structural studies.
• Paramagnetic relaxation enhancement became a major source of structural data.
• Solution NMR structure of membrane protein in lipid nanoparticles is feasible.

Integral membrane proteins (IMPs) play a central role in cell communication with the environment. Their structures are essential for our understanding of the molecular mechanisms of signaling and for drug design, yet they remain badly underrepresented in the protein structure databank. Solution NMR is, aside from X-ray crystallography, the major tool in structural biology. Here we review recently reported solution NMR structures of polytopic IMPs and discuss the new approaches, which were developed in the course of these studies to overcome barriers in the field. Advances in cell-free protein expression, combinatorial isotope labeling, resonance assignment, and collection of structural data greatly accelerated IMP structure determination by solution NMR. In addition, novel membrane-mimicking media made possible determination of solution NMR structures of IMPs in a native-like lipid environment.