Fig. 1

High-resolution ssNMR spectra of NaK. a SF in the crystal structure of KcsA (PDB ID: 1K4C) and NaK (PDB ID: 3E8H). b 2D NCA correlation spectrum of NaK in the presence of 50 mM K⁺ with the signal assignment. SF residues are indicated in bold and the ion-free state is labeled with a prime (′) and in cyan to differentiate it from the K⁺/Rb⁺-favored state (no prime; in black). c Crystal structure of the open state of NaK displaying two opposing subunits. The hinge region is marked with an arrow and assigned residues are indicated on the structure in red. d Amino acid sequence of NaK with secondary structure elements based on the crystal structure indicated above the sequence. Assigned residues are shown in red and SF residues are accentuated by cyan arrows