Figure 8.

Other SAXS/SANS results. A, p(r) derived from the experimental X-ray scattering data (orange) and the 100% scattering data (green), which should approximate the p(r) for PmScsC C87S alone. The p(r) derived from the extended (ext.) crystal structure (Protein Data Bank code 5ID4) is shown as a black dotted line for reference. B, a plot of I(0) normalized by concentration as a function of D₂O content of the supporting solvent. The plot is parabolic in shape and reveals that the match point of the entire complex is 59% D₂O (vertical dotted line). C, Stuhrmann plot for the 3:1 PmScsC C87S–^DPmScsBα C114A complex, conforming to R_g² = R_m² + αΔρ⁻¹ − βΔρ⁻² where R_m is the radius of gyration of that object with homogenous contrast and α and β are related to the contrast variations within the object. The values obtained from a fit to the plot (solid black line) are: R_m = 37.5 ± 0.4, α = −210 ± 50, and β = 520 ± 100. The negative value of α reveals that the region with higher contrast (i.e. ^DPmScsBα C114A) lies toward the center of the molecule. Error bars represent the S.E. D, the composite scattering functions determined from the neutron contrast variation data. The I₁₁ curve (green; left y axis) corresponds to scattering from PmScsC C87S, the I₂₂ curve (blue; left y axis) corresponds to scattering from ^DPmScsBα C114A, and the I₁₂ curve (gray; right y axis) is related to the arrangement of ^DPmScsBα C114A relative to PmScsC C87S. I_homogeneous = I₁₁ + I₂₂ + I₁₂ (red; left y axis) is the scattering curve of an object with the same shape as the PmScsC C87S–^DPmScsBα C114A complex but with homogeneous contrast and is used for estimating the Porod volume and molecular mass from the SANS data.