title: Reconstruction of the complete ouabain-binding pocket of Na,K-ATPase in gastric H,K-ATPase by substitution of only seven amino acids.
abstract: Although cardiac glycosides have been used as drugs for more than 2 centuries and their primary target, the sodium pump (Na,K-ATPase), has already been known for 4 decades, their exact binding site is still elusive. In our efforts to define the molecular basis of digitalis glycosides binding we started from the fact that a closely related enzyme, the gastric H,K-ATPase, does not bind glycosides like ouabain. Previously, we showed that a chimera of these two enzymes, in which only the M3-M4 and M5-M6 hairpins were of Na,K-ATPase, bound ouabain with high affinity (Koenderink, J. B., Hermsen, H. P. H., Swarts, H. G. P., Willems, P. H. G. M., and De Pont, J. J. H. H. M. (2000) Proc. Natl. Acad. Sci. U. S. A. 97, 11209-11214). We also demonstrated that only three amino acids (Phe(783), Thr(797), and Asp(804)) present in the M5-M6 hairpin of Na,K-ATPase were sufficient to confer high affinity ouabain binding to a chimera which contained in addition the M3-M4 hairpin of Na,K-ATPase (Qiu, L. Y., Koenderink, J. B., Swarts, H. G., Willems, P. H., and De Pont, J. J. H. H. M. (2003) J. Biol. Chem. 278, 47240-47244). To further pinpoint the ouabain-binding site here we used a chimera-based loss-of-function strategy and identified four amino acids (Glu(312), Val(314), Ile(315), Gly(319)), all present in M4, as being important for ouabain binding. In a final gain-of-function study we showed that a gastric H,K-ATPase that contained Glu(312), Val(314), Ile(315), Gly(319), Phe(783), Thr(797), and Asp(804) of Na,K-ATPase bound ouabain with the same affinity as the native enzyme. Based on the E(2)P crystal structure of Ca(2+)-ATPase we constructed a homology model for the ouabain-binding site of Na,K-ATPase involving all seven amino acids as well as several earlier postulated amino acids.
authors.affiliation: Department of Biochemistry (160), Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, The Netherlands.
authors.forename: Li Yan
authors.initials: LY
authors.lastname: Qiu
authors.forename: Elmar
authors.initials: E
authors.lastname: Krieger
authors.forename: Gijs
authors.initials: G
authors.lastname: Schaftenaar
authors.forename: Herman G P
authors.initials: HG
authors.lastname: Swarts
authors.forename: Peter H G M
authors.initials: PH
authors.lastname: Willems
authors.forename: Jan Joep H H M
authors.initials: JJ
authors.lastname: De Pont
authors.forename: Jan B
authors.initials: JB
authors.lastname: Koenderink
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004305:Dose-Response Relationship, Drug; D005753:Gastric Mucosa / Q000378:metabolism*; D006027:Glycosides / Q000737:chemistry; D006860:Hydrogen Bonding; D007783:Lactones / Q000737:chemistry; D008024:Ligands; D046911:Macromolecular Substances / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010042:Ouabain / Q000737:chemistry / Q000494:pharmacology*; D010766:Phosphorylation; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D006027:Glycosides; D007783:Lactones; D008024:Ligands; D046911:Macromolecular Substances; D011993:Recombinant Fusion Proteins; D010042:Ouabain; D000251:Adenosine Triphosphatases; D000254:Sodium-Potassium-Exchanging ATPase