Ion-selectivity and mechanisms of the Na/K pump

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Cells maintain large differences in the concentration of ions (electrically charged atoms or molecules) across the membrane that separates the cell from its environment. This concentration difference is used to drive many essential cellular processes and it is established and maintained by numerous membrane pumps, which are proteins responsible for transporting these ions across the membrane. This project will engage undergraduate students (including members of minorities underrepresented in science) and graduate students in investigations of the fundamental properties by which a particular membrane pump selects and transports sodium and potassium ions across membranes. In addition to training in biophysical techniques, the students will be supported to attend national scientific meetings at which they will be able to present the results of their research.The Na/K pump is electrogenic because it transports 3 Na+ out of the cell in exchange for 2 K+, in each catalytic cycle. One out of three sites can exclusively bind Na+ (a feature that distinguishes the Na/K pump from other P-type ATPases). All P-type ATPases alternate between two major conformations, E1 with inward facing ion binding sites and E2 with outward facing ion binding sites. The molecular mechanisms of ion selectivity by the Na/K pump remain unclear, yet knowledge of these is critical to an understanding of how these proteins couple the chemical energy of ATP hydrolysis to the mechanical work required for ion translocation. This project will study the mechanisms of ion selection in the Na/K pump with an innovative approach that integrates high-temporal-resolution electrophysiology, computational chemistry and biochemistry. The available crystal structures and results from our laboratory will be used to generate hypotheses with respect to (a) Elucidating the mechanisms of ion selectivity in the two major pump conformations; (b) Determining the order of intracellular Na+ binding and external Na+ release; and (c) Identifying the pathway and mechanisms of uncoupled H+ influx through Na/K pumps.