Fig. 3: Cryo-electron microscopy structure of the Rhs1-EagR complex.

a P. laumondii Rhs1 cryo-EM density map and model. Unsharpened masked cryo-EM map (left panel – 0.015 contour level) of the Rhs1 β-barrel colored accordingly to the fitted side view of the molecular model (central panel), on a blue (N-terminal) to red (C-terminal) gradient. Slices of the N-terminal (right panel-top) and C-terminal (right panel-bottom) regions are shown in a perpendicular orientation in order to highlight the plugs on each side of the β-barrel, with dotted lines depicting their inner and outer diameters and labels marking the N- and C-terminal sites with respective residue numbers. b Structural evidence for toxin localization inside the Rhs1 β-barrel. Amorphous low-resolution density shown in the center of the β-barrel (left), generated by subtracting all the unsharpened masked map (0.003 contour level) within 2 Å radius of the molecular model, indicated the presence of a highly flexible or unfolded sequence in the central space. By generating a 2 Å molecular density around the model (right panel), the interaction with the N- and C-terminal plugs is evidenced. The N-terminal seal and Ig-like plug domains are shown in blue and cyan, respectively, the C-terminal plug is shown in red, and the C-terminal Rhs1^CT toxin is shown in magenta. c EagR-Rhs1^NT interaction. Density of the N-terminal region in the unmasked map (0.004 contour level) is shown in transparency, with fitted Rhs1 (gray) and EagR dimer model (light and dark green). Only the EagR dimer model is fitted into the Rhs1^NT-EagR density.