1. Introduction 29

2. Landmarks in NMR of macromolecules 32

2.1 Protein structures and methods development 32

2.1.1 Sequential assignment method 32

2.1.2 Triple-resonance experiments 34

2.1.3 Structures of large proteins 36

2.2 Protein–nucleic acid complexes 37

2.3 RNA structures 38

2.4 Membrane-bound systems 39

3. NMR spectroscopy today 40

3.1 State-of-the-art structure determination 41

3.2 New methods 44

3.2.1 Residual dipolar couplings 44

3.2.2 Direct detection of hydrogen bonds 44

3.2.3 Spin labeling 45

3.2.4 Segmental labeling 46

3.3 Protein complexes 47

3.4 Mobility studies 50

3.5 Determination of time-dependent structures 52

3.6 Drug discovery 53

4. The future of NMR 54

4.1 The ease of structure determination 54

4.2 The ease of making recombinant protein 55

4.3 Post-translationally modified proteins 55

4.4 Approaches to large and/or membrane-bound proteins 56

4.5 NMR in structural genomics 56

4.6 Synergy of NMR and crystallography in protein structure determination 56

5. Conclusion 57

6. Acknowledgements 57

7. References 57

Since the publication of the first complete solution structure of a protein in 1985 (Williamson et al. 1985), tremendous technological advances have brought nuclear magnetic resonance spectroscopy to the forefront of structural biology. Innovations in magnet design, electronics, pulse sequences, data analysis, and computational methods have combined to make NMR an extremely powerful technique for studying biological macromolecules at atomic resolution (Clore & Gronenborn, 1998). Most recently, new labeling and pulse techniques have been developed that push the fundamental line-width limit for resolution in NMR spectroscopy, making it possible to obtain high-field spectra with better resolution than ever before (Dötsch & Wagner, 1998). These methods are facilitating the study of systems of ever-increasing complexity and molecular weight.