Figure 2.

Cryo-EM structure of IrtAB _ΔSID (E-Q) in complex with ATP. (A) Two orthogonal views of the ATP-bound IrtAB_ΔSID (E-Q). ATP is represented as a stick model coloured magenta, and Mg²⁺ ions are shown as yellow spheres. (B) Slice-through representation of the internal cavity of IrtAB. The amphipathic cavity is indicated by a dashed red ellipse. (C) View of the NBD dimer from the periplasm. The highly conserved sequence motifs are also indicated. (D) Molecular interactions at the IrtA ATPase site, together with the density map (mesh) for ATP-Mg²⁺ and nearby residues. Conserved key residues are drawn as stick models. Interactions between glutamine in the Q-loop and ATP or Mg²⁺ are indicated by dashed lines. (E) Molecular interactions at the IrtB ATPase site, together with the density map (mesh) for ATP-Mg²⁺ and nearby amino acids. Conserved key residues are drawn as stick models. Interactions between glutamine in the Q-loop and ATP or Mg²⁺ are indicated by dashed lines. (F) The electrostatic inner surface representation of IrtA and IrtB in the occluded conformation. The cavity is outlined with a broken orange line. The surfaces are colored from blue (most positive) to red (most negative). Hydrophobic regions are shown in white. The binding site of the metal ion in IrtA is indicated with a black circle. (G) Superimposition of IrtA (slate) and IrtB (salmon) structures.