Fig. 4: Cryo-EM structures of ErNaR.

a Overall view of the ErNaR pentamer from the extracellular (top) and along the membrane plane (bottom). b Comparison of the hydrophobicity of the concave aqueous basin in the center of the ErNaR and KR2 pentamers. c The region of interprotomeric sodium binding site (according to the KR2 structure) absent in ErNaR. The cryo-EM map (pH 8.0) is shown with black mesh. d The DDM molecule in the cryo-EM structures of ErNaR. 5 molecules of DDM are located between neighboring protomers at the cytoplasmic side of the protein. The polar head of DDM is located next to the entrance to the ion uptake cavity and interacts with the C-terminal helix found in ErNaR. e The central region of the ErNaR protomer at pH 8.0. The cryo-EM map is shown with black mesh and indicates direct interaction between D105 and E64. f The central region of the ErNaR protomer at pH 4.3. The cryo-EM map is shown with black mesh and indicates direct interaction between D105 and E64. The lengths of the H-bonds are given in Å and shown with bold italic numbers.