Introduction 2 The foundations of transverse relaxation-optimized spectroscopy (TROSY) 3 TROSY in NMR experiments with biological macromolecules 4 New stable isotope labeling strategies for TROSY NMR with large structures 5 Combining TROSY with cross correlated relaxation-induced polarization transfer for studies of very large structures 6 Conclusions and outlook 7 References
1 Introduction
NMR spectroscopy with biological macromolecules has been limited to relatively small structures, with molecular weights up to about 50 kDa, and the size distribution of the approximately 2500 NMR deposits in the Protein Data Bank peaks near a molecular weight of 10 kDa. 1 In spite of this limitation, NMR is one of the principal experimental techniques in structural biology. 2,3 Nonetheless, the availability of solution NMR techniques for studies of larger structures is of keen interest, in particular for applications in the newly emerging field of structural and functional genomics. 4 With the presently described principles of transverse relaxationoptimized spectroscopy (TROSY) the size limit for molecular structures that are amenable to high resolution NMR studies in solution has been extended severalfold. 5 -7 TROSY-based NMR experiments are particularly well suited for applications with proteins and nucleic acids, 8 which are a main focus also in the present article.
2 THE FOUNDATIONS OF TRANSVERSE RELAXATION-OPTIMIZED SPECTROSCOPY (TROSY)
At the high magnetic fields typically used for studies of proteins and nucleic acids, chemical shift anisotropy (CSA) of 1 H, 15 N and 13 C nuclei can be a significant source of transverse relaxation, in addition to the omnipresent relaxation due to dipole-dipole coupling. As a consequence the individual multiplet components in heteronuclear two-spin systems, such as 15 N-1 H in amide groups and aromatic 13 C-1 H