Fig. 5. SAXS studies on the binary and ternary PTG-PP1 complexes.

a Shown are I(q) versus q experimental SAXS profiles for apo PTG-PP1 (black dots) and bound to cyclodextrin (blue dots) with the EOM fit (red lines). SAXS curves were obtained through averaging of buffer-background subtracted frames across the entire elution traces of the SEC-SAXS experiments (approximately n = 50 frames averaged, see Supplementary Table 4). Error bars represent an estimate of the experimental error, σ, on the intensity recorded for each value of q assigned by data reduction software^{57, 58}. Chi² values (χ²) for the EOM fitting are indicated. The curves are shifted by an arbitrary offset for better comparison. The lower plots show the error-weighted residual difference plots. b SEC-SAXS chromatograms of PTG-PP1 complex alone and bound to β-cyclodextrin. The black and blue lines represent the total summed scattering intensity for PTG-PP1 and PTG-PP1 + β-cyclodextrin, respectively; triangles represent the calculated radius of gyration, R_g in nm, in the selected frames. c Dimensionless Kratky plots for PTG-PP1 complex alone (black circles) and bound to β-cyclodextrin (blue circles). d Superposition of an illustrative 3D EOM structure describing the ternary complex together with the corresponding X-ray crystal structure solved in this study. All the structures are represented in surface mode. PP1 protein is shown in blue; the PTG segments from residue 83–102 and from 111 to 128 are shown in red; missing PTG residues were modeled with EOM and shown in yellow. In red, the PTG CBM21 domain bound to β-cyclodextrin (in dark gray) in the position interacting with PP1 as observed in the crystal structure. In light green with transparency, the EOM model for PTG CBM21 domain bound to β-cyclodextrin and unbound from PP1.