Fig. 2

Angular motion in the β-turn of MPD-ub crystals probed by NERRD NMR. a, b NERRD dispersion data of the two amide sites in MPD-ub that are adjacent to the flipping peptide plane D52/G53, recorded at 44.053 kHz MAS frequency. Error bars of R _1ρ values were obtained by standard Monte Carlo analyses, described in the Methods section. Solid lines show fit curves from a two-site jump model that assumes that the minor conformation has a population of p _B = 10%. c χ ² surface of a grid-search of simulated NERRD curves against the experimental data in a, b. Hereby, a common minor-state population p _B and exchange correlation time τ _ex = 1/(k _AB + k _BA) were assumed for the two residues, and the jump angle was separately fitted for each residue. More details of this NERRD fit are reported in Supplementary Fig. 4. d Cross-section across the χ ² surface along the τ _ex dimension corresponding to a minor-state population of 10%. This minor-state population level is suggested by analyses of BMCRD data, as explained in the text. The best-fit exchange time constant with this assumption is τ _ex ~ 100 μs