Fig. 4: Two ligand-binding sites in EcmrR.

a Overview of two ligand-bindings sites in EcmrR. Only the CTD of one EcmrR subunit is shown. Two bound ligands, TPSb⁺ and CHAPSO, are displayed as green sticks and are superimposed with the cryo-EM density (blue surfaces) contoured at 7σ. b Interactions between TPSb⁺ and EcmrR in ligand-binding site I. Ligand-interacting residues in EcmrR are shown as orange sticks. c Interactions between CHAPSO and EcmrR in ligand-binding site II. Ligand-interacting residues in EcmrR are shown as orange sticks. Hydrogen bonds are shown as gray dotted lines. d Comparison of EcmrR ligand-binding site I between the CTA⁺-bound and TPSb⁺-bound forms. Crystal structure of EcmrR CTD/CTA⁺ complex is superimposed with the structure of EcmrR/TPSb⁺/CHAPSO subcomplex in EcmrR-RP_itc-4nt. Ligands are shown in ball-and-stick representation and EcmrR residues contacted by ligands are shown in stick representation. e Comparison of EcmrR ligand-binding site II among the unbound, CTA⁺-bound and CHAPSO-bound forms. Crystal structure of EcmrR CTD/CTA⁺ complex and EcmrR/TPSb⁺ subcomplex in EcmrR-RP_itc-3nt are superimposed with the structure of EcmrR/TPSb⁺/CHAPSO subcomplex in EcmrR-RP_itc-4nt. f Pseudo two-fold symmetry of EcmrR CTD. The structure of EcmrR CTD with TPSb⁺ and CHAPSO bound to its two ligand-binding sites is rotated 180° along a hypothetical axis (indicated by a black ellipse) and overlapped with the original structure.