title: Protonation of key acidic residues is critical for the K⁺-selectivity of the Na/K pump.
abstract: The sodium-potassium (Na/K) pump is a P-type ATPase that generates Na(+) and K(+) concentration gradients across the cell membrane. For each hydrolyzed ATP molecule, the pump extrudes three Na(+) and imports two K(+) by alternating between outward- and inward-facing conformations that preferentially bind K(+) or Na(+), respectively. Remarkably, the selective K(+) and Na(+) binding sites share several residues, and how the pump is able to achieve the selectivity required for the functional cycle is unclear. Here, free energy-perturbation molecular dynamics (FEP/MD) simulations based on the crystal structures of the Na/K pump in a K(+)-loaded state (E2·P(i)) reveal that protonation of the high-field acidic side chains involved in the binding sites is crucial to achieving the proper K(+) selectivity. This prediction is tested with electrophysiological experiments showing that the selectivity of the E2P state for K(+) over Na(+) is affected by extracellular pH.
authors: Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA.
authors: Haibo
authors: H
authors: Yu
authors: Ian M
authors: IM
authors: Ratheal
authors: Pablo
authors: P
authors: Artigas
authors: Benoît
authors: B
authors: Roux
mesh_terms: D000143:Acids / Q000737:chemistry*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D056004:Molecular Dynamics Simulation; D016297:Mutagenesis, Site-Directed; D011188:Potassium / Q000378:metabolism*; D011522:Protons; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*
chemical_list: D000143:Acids; D011522:Protons; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium