Three-dimensional structure of renal Na,K-ATPase determined from two-dimensional membrane crystals of the p1 form

Electron microscopy and image processing were used to reconstruct a three-dimensional model of membrane-bound monomeric renal Na,K-ATPase from negatively stained two-dimensional crystals of the p1 type. Correlation methods were applied to obtain projection averages which were aligned by a phase difference minimization procedure. The self-consistency of the reconstruction process was high as determined by correlation between experimental projections and projections of the calculated model. The three-dimensional model of the Na,K-ATPase protomer in the p1 crystal form contains three characteristic domains, a protein dense ellipsoid, a small globular stain deficient domain, and a connecting low-contrast region. The latter is thought to correspond to the lipid-penetrating part of the Na,K-ATPase protomer. The location of this domain gives the protein an asymmetric distribution in the bilayer so that it is exposed primarily on one side proposed to correspond to the intracellular face.