Figure 5
A putatively conserved intramolecular signaling pathway for TaHeR and HeR 48C12. (a) TaHeR dimer structure at pH 8 (cyan, PDB ID 6is6) and pH 4.5 (yellow, PDB ID 7u55). (b) HeR 48C12 dimer structure at pH 8.8 (green, PDB ID 6su3) and pH 4.3 (pink, PDB ID 6su4). The conserved intramolecular signaling mechanism involves a negatively charged anion (chloride or acetate) occupying the SBC (grey surface), switching the orientation of His-23, displacing water molecules (red arrows), disordering Gln-26 and disordering Trp-243 (in TaHeR) or Trp-246 (in HeR 48C12). The overlay reveals there is a 1 Å movement of the intracellular B–C loop. TaHeR has an additional 6 Å shift of the A − B tail from the electrostatic attraction of Tyr-48 and Asn-53 to an external chloride ion. Waters are shown as small spheres colored to match protein, and chloride ions as large green spheres (belonging to pH 4.5 TaHeR only). The 2Fo − Fc maps (blue mesh) are contoured at 1 σ, and Fo − Fc is contoured at + 3 σ for positive (green mesh) and − 3 σ for negative (red mesh) electron density, respectively. ‡ In HeR 48C12 at pH 4.3, there is no electron density to account for this water in the chain A protomer.
