Structure-function relationships of cation translocation by Ca(2+)- and Na+, K(+)-ATPases studied by site-directed mutagenesis.
Site-directed mutagenesis studies of the sarcoplasmic reticulum Ca(2+)-ATPase have pinpointed five amino acid residues that are essential to Ca2+ occlusion, and these residues have been assigned to different parts of a Ca2+ binding pocket with channel-like structure. Three of the homologous Na+, K(+)-ATPase residues have been shown to be important for binding of cytoplasmic Na+ at transport sites. In addition, three of the above mentioned Ca(2+)-ATPase residues appear to participate in the countertransport of H+, and two of the Na+, K(+)-ATPase residues to participate in the countertransport of K+. Residues involved in energy transducing conformational changes have also been identified by mutagenesis. In the Ca(2+)-ATPase, ATP hydrolysis is uncoupled from Ca2+ transport following mutation of a tyrosine residue located at the top of transmembrane segment M5. This tyrosine, present also in the Na+, K(+)-ATPase, may play a critical role in closing the gate to a transmembrane channel.
Andersen
J P
JP
Danish Biomembrane Research Centre, University of Aarhus, Denmark.
Vilsen
B
B
D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D017136:Ion Transport; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship
D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium