Protein Structure Determination in Living Cells from NOE-derived Distance Restraints

In-cell NMR has uncovered various protein behaviours in cells or molecular crowding environments, such as protein stability, dynamics, and global structural conformation. Among these remarkable potential abilities of this method, in-cell NMR protein structure determination is particularly beneficial in terms of providing the most accurate and intuitive views for protein states in intracellular environments. In order to elucidate sufficiently detailed conformations at atomic resolution including side-chain in cells, it remains necessary to address de novo protein structure determination based on distance restraints derived from three-dimensional (3D) NOESY experiments. While the short lifetime of cells and target proteins, severe signal overlaps, background noise signals, sample inhomogeneity, etc. had prevented the efficient determination of 3D structures of bio-macromolecules, new technologies for sample preparations, NMR measurements, and structure calculation overcame these problems and made it possible to determine the conformations of small-size proteins with molecular weights of approximately 10 kDa. These methodologies extend the possibility of the NMR analysis of proteins in living systems. In this chapter, we introduce current progress for the structure determination of proteins in living systems and give an outlook into future areas of research and application of cellular solution-state NMR spectroscopy.