Stable-Isotope-Aided NMR Spectroscopy

Boundless progress in isotope-aided NMR methods still continues to provide the driving force for developing novel NMR strategies for structural biology research of proteins. In the first edition of this book, we described an overview of the isotope labeling methods available at that time. In this second edition, we will mainly focus on newer isotope-aided NMR methods, such as the methyl-specific labeling and stereo-array isotope labeling (SAIL) methods, which have rapidly developed during the past decade. The methyl-specific labeling is currently used as the most practical technique applicable to large protein complexes and membrane proteins. The standard methyl labeling protocols employ isotope-labeled α-keto acid precursors, which enable selective observations of the methyl groups of Ile, Leu, and Val residues. More recently, the stereo-specific isotope labeling methods of prochiral methyl groups have become available, using either regio-selectively isotope-labeled precursors or stereo-specifically (13)CH(3)-labeled amino acids. We also focus on the stereo-array isotope labeling (SAIL) method, which is a breakthrough isotope labeling technology using stereo- and regio-selectively [(2)H, (13)C, (15)N]-labeled amino acids with isotope labeling patterns optimized for NMR studies. Various applications of SAIL and related methods to structural studies, including protein dynamics such as aromatic ring-flipping motions, hydrogen-deuterium exchange rates, conformational analysis, and dynamics about disulfide bonds, will be discussed.