Biophys J, May 2001, p. 2187-2197, Vol. 80, No. 5

Structure of Na⁺,K⁺-ATPase at 11-Å Resolution: Comparison with Ca²⁺-ATPase in E₁ and E₂ States

William J. Rice,^* Howard S. Young,^* Dwight W. Martin, John R. Sachs, and David L. Stokes^*

 ^*Skirball Institute of Biomolecular Medicine and Department of Cell Biology, New York University Medical Center, New York, New York 10016, and  Division of Hematology, Department of Medicine, State University of New York at Stony Brook, Stony Brook, New York 11794 USA

Na⁺,K⁺-ATPase is a heterodimer of  and  subunits and a member of the P-type ATPase family of ion pumps. Here we present an 11-Å structure of the heterodimer determined from electron micrographs of unstained frozen-hydrated tubular crystals. For this reconstruction, the enzyme was isolated from supraorbital glands of salt-adapted ducks and was crystallized within the native membranes. Crystallization conditions fixed Na⁺,K⁺-ATPase in the vanadate-inhibited E₂ conformation, and the crystals had p1 symmetry. A large number of helical symmetries were observed, so a three-dimensional structure was calculated by averaging both Fourier-Bessel coefficients and real-space structures of data from the different symmetries. The resulting structure clearly reveals cytoplasmic, transmembrane, and extracellular regions of the molecule with densities separately attributable to  and  subunits. The overall shape bears a remarkable resemblance to the E₂ structure of rabbit sarcoplasmic reticulum Ca²⁺-ATPase. After aligning these two structures, atomic coordinates for Ca²⁺-ATPase were fit to Na⁺,K⁺-ATPase, and several flexible surface loops, which fit the map poorly, were associated with sequences that differ in the two pumps. Nevertheless, cytoplasmic domains were very similarly arranged, suggesting that the E₂-to-E₁ conformational change postulated for Ca²⁺-ATPase probably applies to Na⁺,K⁺-ATPase as well as other P-type ATPases.

Biophys J, May 2001, p. 2187-2197, Vol. 80, No. 5
© 2001 by the Biophysical Society   0006-3495/01/05/2187/11  $2.00

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