Figure 6. Comparison of EspG₅-PE25-PPE41 and EspG₃-PE5-PPE4¹⁻¹⁷⁸ complexes structures.

(a) SAXS-based ab initio models of the EspG_5mtu-PE25-PPE41 complex (purple) and the EspG_3msm-PE5–PPE4¹⁻¹⁷⁸ complex (green) reveal a more extended conformation of the EspG_3msm-PE5–PPE4¹⁻¹⁷⁸ complex, as indicated by the maximum diameter (D_max) and radius of gyration (R_g) of each complex. (b) Experimental SAXS data (black circles) with the computed fits (solid lines) and the respective discrepancy values (χ²) for EspG_5mtu-PE25- PPE41 and EspG_3msm-PE5-PPE4 protein complexes. The theoretical SAXS curve, calculated with CRYSOL from the EspG_5mtu-PE25–PPE41 complex structure (PDB ID 4KXR), fits the experimental SAXS data with a goodness-of-fit (χ²) of 0.95 (purple). The theoretical SAXS curve calculated from the EspG_3msm rigid-body model in complex with a homology model of PE5-PPE4¹⁻¹⁷⁸ fits the experimental SAXS data (green) with a goodness- of-fit values (χ²) of 1.40. (c) Superposition of the crystal structure of EspG_5mtu-PE25-PPE41 (purple-lilac-light pink) and the SAXS-derived rigid body model of EspG_3msm-PE5-PPE4¹⁻¹⁷⁸ (dark green-light green-light blue). (d) Hydrophobicity surface representation of EspG proteins with PPE-interacting surface highlighted in transparent pink (left panel). Interaction interface of EspG_5mtu-PPE41 and EspG_3msm-PPE4, with PPE-PE proteins represented as cartoon and EspG proteins as surface with the contact residues in the interface colored in light pink in each EspG protein (right panel).