The Crystallographic Structure of Na,K-ATPase N-domain at 2.6 Å Resolution

The structure of the N-domain of porcine α2 Na,K-ATPase was determined crystallographically to 3.2 Å resolution by isomorphous heavy-atom replacement using a single mercury derivative. The structure was finally refined against 2.6 Å resolution synchrotron data. The domain forms a seven-stranded antiparallel β-sheet with two additional β-strands forming a hairpin and five α-helices. Approximately 75% of the residues were superimposable with residues from the structure of Ca-ATPase N-domain, and a structure-based sequence alignment is presented. The positions of key residues are discussed in relation to the pattern of hydrophobicity, charge and sequence conservation of the molecular surface. The structure of a hexahistidine tag binding to nickel ions is presented.