title: The rapid-onset dystonia parkinsonism mutation D923N of the Na+, K+-ATPase alpha3 isoform disrupts Na+ interaction at the third Na+ site.
abstract: Rapid-onset dystonia parkinsonism (RDP), a rare neurological disorder, is caused by mutation of the neuron-specific alpha3-isoform of Na(+), K(+)-ATPase. Here, we present the functional consequences of RDP mutation D923N. Relative to the wild type, the mutant exhibits a remarkable approximately 200-fold reduction of Na(+) affinity for activation of phosphorylation from ATP, reflecting a defective interaction of the E(1) form with intracellular Na(+). This is the largest effect on Na(+) affinity reported so far for any Na(+), K(+)-ATPase mutant. D923N also affects the interaction with extracellular Na(+) normally driving the E(1)P to E(2)P conformational transition backward. However, no impairment of K(+) binding was observed for D923N, leading to the conclusion that Asp(923) is specifically associated with the third Na(+) site that is selective toward Na(+). The crystal structure of the Na(+), K(+)-ATPase in E(2) form shows that Asp(923) is located in the cytoplasmic half of transmembrane helix M8 inside a putative transport channel, which is lined by residues from the transmembrane helices M5, M7, M8, and M10 and capped by the C terminus, recently found involved in recognition of the third Na(+) ion. Structural modeling of the E(1) form of Na(+), K(+)-ATPase based on the Ca(2+)-ATPase crystal structure is consistent with the hypothesis that Asp(923) contributes to a site binding the third Na(+) ion. These results in conjunction with our previous findings with other RDP mutants suggest that a selective defect in the handling of Na(+) may be a general feature of the RDP disorder.
authors.affiliation: Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Department of Physiology and Biophysics, Aarhus University, DK-8000 Aarhus C, Denmark.
authors.forename: Anja Pernille
authors.initials: AP
authors.lastname: Einholm
authors.forename: Mads S
authors.initials: MS
authors.lastname: Toustrup-Jensen
authors.forename: Rikke
authors.initials: R
authors.lastname: Holm
authors.forename: Jens Peter
authors.initials: JP
authors.lastname: Andersen
authors.forename: Bente
authors.initials: B
authors.lastname: Vilsen
mesh_terms: D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002522:Chlorocebus aethiops; D020821:Dystonic Disorders / Q000235:genetics; D006801:Humans; D020125:Mutation, Missense; D020734:Parkinsonian Disorders / Q000235:genetics*; D011188:Potassium; D011485:Protein Binding; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics* / Q000378:metabolism
chemical_list: D011188:Potassium; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; C488756:ATP1A3 protein, human