Figure 2.

Na⁺-occupancy dependent conformational change in NCX_Mj. (a) Superimposition of the NCX_Mj crystal structures obtained in high (100 mM, cyan cylinders) and low (10 mM, brown cylinders) Na⁺ concentrations. (b) Close-up view of the interface between TM6 and TM7ab in the NCX_Mj structures obtained at high and low Na⁺ concentrations (top and lower panels, respectively). Residues forming van-der-Waals contacts in the structure at low Na⁺ concentration are shown in detail. (c) Close-up view of the Na⁺-binding sites. The vacant S_ext site in the structure at low Na⁺ concentration is indicated with a white sphere. Residues surrounding this site are also indicated; note A206 (labeled in red) coordinates Na⁺ at S_ext via its backbone carbonyl oxygen. (d) Extracellular solvent accessibility of the ion binding sites in the structures at high and low [Na⁺]. Putative solvent channels are represented as light-purple surfaces.