Fig. 6.

Determination of ApSOD dimer assembly and an ab initio structure in solution by SAXS. (a) Comparison of the experimental SAXS profile for ApSOD (black dots) to scattering profiles calculated from crystal structures of the bacterial SOD dimer from A. pleuropneumoniae (magenta line) and of HsSOD, both as a single subunit (orange line) and dimer (blue line), indicate that ApSOD assembles as a human-like SOD dimer. (b) Comparison of the experimental SAXS profile for ApSOD (black dots) to scattering profiles calculated from the crystallographically defined ApSOD subunit (red line) and dimer (green line) further supports ApSOD dimer assembly. (c) Comparison of the P(r) pairwise interatomic distance functions from ApSOD SAXS data (black line) with P(r) functions calculated for the single subunit (red line) and dimer (green line) crystal structure models confirms dimer assembly in solution. Scattering intensity (ordinate) is plotted against the interatomic pair distances (abscissa). (d and e) X-ray crystal structure of the crystallographic symmetry-related ApSOD dimer model (ribbon diagram) docked into an ab initio SAXS structure solution (surface).