Structure‐function relationships of cation translocation by Ca2+‐ and Na+,K+‐ATPases studied by site‐directed mutagenesis

[摘要]

Site-directed mutagenesis studies of the sarcoplasmic reticulum Ca²⁺-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 Ca²⁺-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 Ca²⁺-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.

[学科分类] 生物化学/生物物理

[关键词] P-type ATPase;Calcium;Sodium;Potassium;Ion pump;Ion channel;CrATP;βγ-bidentate chromium(III) complex of ATP;K 0.5;concentration giving half maximal activation;M1-M10;putative transmembrane segments numbered from the NH2-terminal end of the peptide;wild type;the non-mutated form of the exogenous enzyme expressed following transfection