Jp. Andersen et B. Vilsen, STRUCTURE-FUNCTION-RELATIONSHIPS OF CATION TRANSLOCATION BY CA2-ATPASE AND NA+,K+-ATPASE STUDIED BY SITE-DIRECTED MUTAGENESIS(), FEBS letters, 359(2-3), 1995, pp. 101-106
Site-directed mutagenesis studies of the sarcoplasmic reticulum Ca2+-A
TPase have pinpointed five amino acid residues that are essential to C
a2+ occlusion, and these residues have been assigned to different part
s of a Ca2+ binding pocket with channellike structure, Three of the ho
mologous Na+,K+-ATPase residues have been shown to be important for bi
nding of cytoplasmic Na+ at transport sites. In addition, three of the
above mentioned Ca2+-ATPase residues appear to participate in the cou
ntertransport of K+, and two of the Na+,K+-ATPase residues to particip
ate in the countertransport of KC, Residues involved in energy transdu
cing conformational changes have also been identified by mutagenesis.
In the Ca2+-ATPase, ATP hydrolysis is uncoupled from Ca2+ transport fo
llowing mutation of a tyrosine residue located at the top of transmemb
rane segment M5. This tyrosine, present also in the Na+,K+-ATPase, may
play a critical role in closing the gate to a transmembrane channel.