Figure 1. and coupling constant values in proteins.

Figure 2. HNCA and HN(CO)CA experiments are used in tandem to achieve the assignment of H ^N, N, and C ^α backbone resonances. Pairs of strips are obtained at a given chemical shift value, which corresponds to the chemical shift value of an amide nitrogen. At the frequency of the attached H ^N _i , a connectivity to the C ^α of the previous amino acid is observed in the HN(CO)CA experiment (left strip in the pair, blue peak), while connectivities to both the C ^α of the same amino acid and the C ^α of the previous amino acid are present in the HNCA experiment (right strip in the pair, red peaks). The sequential assignment is made by matching the C ^α chemical shifts.

Figure 3. The HCCH‐TOCSY experiment is specifically designed to correlate side‐chain aliphatic proton and resonances via and coupling constants. Using known C ^α and C ^β chemical shifts from the backbone assignment one can get the H ^α and H ^β chemical shifts by finding strips at each carbon shift that have peaks at the same hydrogen chemical shift values. Further peaks for the H ^γ and H ^δ atoms (if present in that particular amino acid type) will be visible in the same strip, which in turn will allow identification of the carbons they are attached to.

Figure 4. Number of new entries deposited in the BMRB in the past 15 years, separated on the basis of the labeling scheme employed (entries with the tag refer to deuterated samples).(Data for this figure have been kindly provided by W. Vranken, Vrije Universiteit Brussel.)

Figure 5. Calibration of experimental NOESY volumes, showing experimental volumes versus actual distances in the structure. The continuous line represents the calibration curve for the upper limits according to Equation 2.

Figure 6. Illustration of the relationship between the standard protein dihedral angle χ ₁ and the angle θ that can be derived from the measurement of the coupling between the and H ^{β 2} nuclei through Equation 3 (χ ₁ = θ – offset, see Table 2).

Figure 7. Values of selected couplings as a function of the standard protein dihedral angle ϕ (see also Table 2).

Figure 8. Alignment of a protein in an orienting solution (the molecules of the orienting medium are depicted as green rods). The rods align with the magnetic field due to their large magnetic anisotropy; the protein interacts weakly with the rod‐shaped molecules, yielding a partial alignment of the protein molecules. This allows the measurement of RDCs for, for example, the – moieties.

Figure 9. Diagram of the CYANA representation of a protein covalent structure. Each number next to an arrow connecting two rigid blocks (circles) corresponds to an adjustable torsion angle.

Figure 10. Overview of the standard simulated annealing protocol in CYANA.

Figure 11. Diagram of a rMD approach to energy refinement of NMR structures. The initial minimization is mainly aimed at adjusting the solvation shell, with the protein often frozen. All other stages are run with all experimental restraints active.

Figure 12. Schematic illustration of the molecular fragment replacement procedure implemented for chemical shift‐based structure calculations. (Reprinted with permission from [ 110]. © 2007 National Academy of Sciences USA.)

Figure 13. NMR observables that can be used to monitor dynamic processes on different timescales, as discussed in this chapter.

Figure 14. Schematic representation of the monodimensional NMR spectrum for a nucleus exchanging between two distinct chemical environments A and B, with populations P _A and P _B in the ratio 3 : 1. When the rate of exchange k _ex is much slower than the difference in chemical shift (expressed in frequency units; k _ex ≪ Δν _AB = Δω _AB/2π), two separate peaks are observed for the two states, with relative intensities corresponding to the relative populations. In the fast exchange regime (k _ex ≫ Δν _AB = Δω _AB/2π), only one signal is observed at a population‐weighted average chemical shift. At intermediate exchange regimes the linewidth is increased via exchange broadening.

Figure 15. Plot of the logT _i (i = 1,2) and – NOE versus‐logτ _m. The curves are calculated with the assumption that the H–N bond vector has S ² = 1 and is relaxed by – dipolar coupling and CSA.

Figure 16. Diagram of the NH exchange mechanism.