Comparative modeling of the H4-H5-loop of the α2-isoform of Na+/K+-ATpase α-subunit in the E1 conformation

Restraint-based comparative modeling was used for calculation and visualization of the H4-H5-loop of Na+/K+-ATPase from mouse brain (Mus musculus, adult male brain, α2-isoform) between the amino acid residues Cys336 and Arg758 in the E1 conformation The structure consists of two well separated parts. The N-domain is formed by a seven-stranded antiparallel β-sheet with two additional β-strands and five α-helices sandwiching it, the P-domain is composed of a typical Rossman fold. The ATP-binding site was found on the N-domain to be identical in both α2- and α1-isoforms. The phosphorylation Asp369 residue was found in the central part of the P-domain, located at the C-terminal end of the central β-sheet. The distance between the α-carbon of Phe475 at the ATP-binding site and the α-carbon of Asp369 at the phosphorylation site is 3.22 nm. A hydrogen bond between the oxygen atom of Asp369 and the nitrogen atom of Lys690 was clearly detected and assumed to play a key role in maintaining the proper structure of the physphorylaton site in E1 conformation.