Structure of two-dimensional crystals of membrane-bound Na,K-ATPase as analyzed by correlation averaging

The structure of two-dimensional crystals of membrane-bound Na,K-ATPase from rabbit kidney has been analyzed with a correlation averaging procedure. Two principally different crystal forms are observed with p1 and p21 symmetry, respectively. In the p1 form the averaged projection structure shows a triangular shaped protein domain interpreted as a protomer (alpha beta-unit) of Na,K-ATPase. In the p21-form the stain-deficient area is extended toward a twofold symmetry axis. The results are in good agreement with a previous analysis where Fourier methods were applied to well ordered crystals of pig kidney Na,K-ATPase and illustrate that the correlation averaging procedure can be used for the analysis of membrane crystals of Na,K-ATPase showing curved lattice lines.