Figure 4: Structural characterization of ΔspMBP-EmrE-ApoAI* by SAXS.

(a–c) Multiple views of the reconstructed particle envelope calculated ab initio from the dimer SAXS data (red circles in d) using DAMMIF³⁵. The structural model with the lowest χ²-value is docked into the envelope using SUPCOMB. The images represent (a) side view, (b) lateral view, rotated −90° around z axis from view in (a) and (c) top view, rotated −90° around y axis from view in (a). ΔspMBP proteins were removed from the representation in (c) to enhance the visualization of the modelled interactions between EmrE and ApoAI*. The model was constructed using ΔspMBP crystal structure (pdb ID: 1NL5), ApoAI lipid-free crystal structure (pdb ID: 2A01) and electron microscopy-derived structure of dimeric EmrE (pdb ID: 2I68). EOM analysis provided the structural framework for this model. (d) Comparison between the experimental scattering profile of the dimer (red circles) and the theoretical profile calculated for the proposed model using CRYSOL (solid line). Goodness of fit is accessed by a χ²-test. A χ²-value of 0.174 indicates that the calculated SAXS curve agrees with the experiment data within error, consistent with the good alignment observed between the proposed model and the reconstruction in (a–c).