Figure 8.
Small-angle X-ray scattering data. A, Guinier plots of X-ray small-angle scattering intensities measured at four concentrations of LpoA. Shown are the Rg values derived from the linear portion of the Guinier plot. The reciprocal lattice vector length q is 4πsinθ/λ (wave number). The plot was in the q range, where Rg × qmax is ≤1.3. B, this Guinier plot obtained after data extrapolation to zero protein concentration gives a radius of gyration of 32.65 Å. C, the Porod-Debye plot does not have the typical Porod plateau, indicating a flexible protein structure (40). D, SAXS data are plotted as a dimensionless Kratky plot based on Rg (41). See “Results” for significance. E, predicted scattering from the NMA(LpoAOrt) structure (red) fit best to the experimental scattering curve (black) with χ = 1.25. The lower section of the graph shows the residual, calculated as the ratio between the two curves. F, same as E, but the scattering curve (red) for a 3-model ensemble (LpoAOrt, NMA(LpoAOrt), NMA(LpoAMon2)) is fit to the observed data (black) with χ = 0.80. G, the three structures constituting the ensemble. The most extended structure in the ensemble, NMA(LpoAMon2B), has a 45% volume fraction, suggesting that it is a significant conformer in solution. H, pairwise distance–distribution plot, P(r). The maximal distance (Dmax) of 118 Å derived from this is consistent with the most extended structure considered here, NMA(LpoAMon2B), with maximum interatomic distance of 116.7 Å.