Displacement of the Na+/K+ Pump's Transmembrane Domains Demonstrates Conserved Conformational Changes in P-type 2 ATPases.

Significance The P-type 2 ATPase subfamily includes several essential primary active ion transporters like the Na + /K + , H + /K + , and SERCA pumps. These transporters are thought to act by a conserved mechanism. However, major conformational changes seen in the transmembrane domains in crystal structures of SERCA and also proposed to occur in H + /K + pumps are absent in available Na + /K + -pump structures. Here we use cross-linking of engineered cysteines and voltage clamp fluorometry (VCF) to show that the movements of transmembrane segments conserved in other pumps, which are absent in Na + /K + pump crystal structures, occur in functional Na + /K + pumps. In addition, we illustrate a twist to the usual VCF approach that may help in future studies using this technique with other membrane proteins.