title: Structural identification of cation binding pockets in the plasma membrane proton pump.
abstract: The activity of P-type plasma membrane H(+)-ATPases is modulated by H(+) and cations, with K(+) and Ca(2+) being of physiological relevance. Using X-ray crystallography, we have located the binding site for Rb(+) as a K(+) congener, and for Tb(3+) and Ho(3+) as Ca(2+) congeners. Rb(+) is found coordinated by a conserved aspartate residue in the phosphorylation domain. A single Tb(3+) ion is identified positioned in the nucleotide-binding domain in close vicinity to the bound nucleotide. Ho(3+) ions are coordinated at two distinct sites within the H(+)-ATPase: One site is at the interface of the nucleotide-binding and phosphorylation domains, and the other is in the transmembrane domain toward the extracellular side. The identified binding sites are suggested to represent binding pockets for regulatory cations and a H(+) binding site for protons leaving the pump molecule. This implicates Ho(3+) as a novel chemical tool for identification of proton binding sites.
authors.affiliation: Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation Gustav Wieds Vej 10C, DK-8000 Aarhus C, Denmark.
authors.forename: Kira
authors.initials: K
authors.lastname: Ekberg
authors.forename: Bjørn P
authors.initials: BP
authors.lastname: Pedersen
authors.forename: Danny M
authors.initials: DM
authors.lastname: Sørensen
authors.forename: Ann K
authors.initials: AK
authors.lastname: Nielsen
authors.forename: Bjarke
authors.initials: B
authors.lastname: Veierskov
authors.forename: Poul
authors.initials: P
authors.lastname: Nissen
authors.forename: Michael G
authors.initials: MG
authors.lastname: Palmgren
authors.forename: Morten J
authors.initials: MJ
authors.lastname: Buch-Pedersen
mesh_terms: D001665:Binding Sites; D002412:Cations / Q000737:chemistry*; D002462:Cell Membrane / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005816:Genetic Complementation Test; D008670:Metals / Q000737:chemistry; D008969:Molecular Sequence Data; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D017494:Proton Pumps / Q000737:chemistry* / Q000235:genetics; D011522:Protons; D012441:Saccharomyces cerevisiae
chemical_list: D002412:Cations; D008670:Metals; D017494:Proton Pumps; D011522:Protons