Fig. 1: Cryo-EM structure of VcINDY in the C_i-Na⁺ state determined in 300 mM Na⁺.

a Measurements of succinate binding to detergent-purified VcINDY in the presence of 100 mM NaCl, using intrinsic tryptophan fluorescence quenching (N = 4). Data are presented as mean values ± SEM. The apparent K_d was determined to be 92.2 ± 47.4 mM. When NaCl was replaced with Choline chloride, no binding of succinate to VcINDY could be measured (N = 4). b Cryo-EM map of VcINDY determined in the presence of 300 mM NaCl. The map is colored by local resolution (Å) and contoured at 5.1 σ. The overall map resolution is 2.83 Å. c Structure of VcINDY in the C_i-Na⁺ state. The structure is colored by the B-factor. d Na1 site structure and Coulomb map. e Na2 site structure and Coulomb map. f Overlay of VcINDY structures around the substrate and sodium binding sites in the C_i-Na⁺ state (green) and C_i-Na⁺-S state (PDB ID: 5UL7, blue). There is very little structural change observed between the two states.