Structure-function relationships of Na(+), K(+), ATP, or Mg(2+) binding and energy transduction in Na,K-ATPase.
The focus of this article is on progress in establishing structure-function relationships through site-directed mutagenesis and direct binding assay of Tl(+), Rb(+), K(+), Na(+), Mg(2+) or free ATP at equilibrium in Na,K-ATPase. Direct binding may identify residues coordinating cations in the E(2)[2K] or E(1)P[3Na] forms of the ping-pong reaction sequence and allow estimates of their contributions to the change of Gibbs free energy of binding. This is required to understand the molecular basis for the pronounced Na/K selectivity at the cytoplasmic and extracellular surfaces. Intramembrane Glu(327) in transmembrane segment M4, Glu(779) in M5, Asp(804) and Asp(808) in M6 are essential for tight binding of K(+) and Na(+). Asn(324) and Glu(327) in M4, Thr(774), Asn(776), and Glu(779) in 771-YTLTSNIPEITP of M5 contribute to Na(+)/K(+) selectivity. Free ATP binding identifies Arg(544) as essential for high affinity binding of ATP or ADP. In the 708-TGDGVND segment, mutations of Asp(710) or Asn(713) do not interfere with free ATP binding. Asp(710) is essential and Asn(713) is important for coordination of Mg(2+) in the E(1)P[3Na] complex, but they do not contribute to Mg(2+) binding in the E(2)P-ouabain complex. Transition to the E(2)P form involves a shift of Mg(2+) coordination away from Asp(710) and Asn(713) and the two residues become more important for hydrolysis of the acyl phosphate bond at Asp(369).
Jorgensen
P L
PL
Biomembrane Center, August Krogh Institute, Copenhagen University, Universitetsparken 13, 2100 OE, Copenhagen, Denmark. pljorgensen@aki.ku.dk
Pedersen
P A
PA
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D001665:Binding Sites; D002412:Cations; D002462:Cell Membrane / Q000378:metabolism; D004735:Energy Transfer; D018698:Glutamic Acid / Q000378:metabolism; D006801:Humans; D008024:Ligands; D008274:Magnesium / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D011188:Potassium / Q000378:metabolism*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013691:Tellurium / Q000378:metabolism
D002412:Cations; D008024:Ligands; D011994:Recombinant Proteins; D001224:Aspartic Acid; D018698:Glutamic Acid; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D012413:Rubidium; D013691:Tellurium; D011188:Potassium