The 'lysine cluster' in the N-terminal region of Na+/K(+)-ATPase alpha-subunit is not involved in ATPase activity.
The alpha-subunit of the Na+/K(+)-ATPases from several animal species have markedly similar amino acid sequences. However, the N-terminal sequences of the alpha-subunit are rather divergent except for lysine-rich sequences, the 'lysine cluster'. Here we report that the alpha-subunit from frog (Rana catesbeiana) has an N-terminal sequence with the 29 amino acid residues shorter than that of the Xenopus alpha-subunit deduced from its cDNA and hence lacks the 'lysine cluster'. Nevertheless, the Rana enzyme still exhibits ATPase activity. The ATP-dependent Na+ transport activity of the Rana enzyme was similar to that of the dog enzyme, which contains the 'lysine cluster'. Moreover, the Torpedo alpha-subunits deprived of the 'lysine cluster' by means of two gene deletions showed the same Na+/K(+)-ATPase activities as that of the wild type when expressed in Xenopus oocytes from their mRNAs. These results strongly suggest that the 'lysine cluster' in the N-terminal region of the alpha-subunit is not involved in the ATPase and ion transport activities. Since an active alpha-subunit was translated in Xenopus oocytes from mRNA lacking the N-terminal region including the 'lysine cluster', these regions were proved not to function as a membrane insertion signal sequence.
Ohta
T
T
Department of Biochemistry, Jichi Medical School, Tochigi, Japan.
Noguchi
S
S
Nakanishi
M
M
Mutoh
Y
Y
Hirata
H
H
Kagawa
Y
Y
Kawamura
M
M
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002872:Chromosome Deletion; D007668:Kidney / Q000201:enzymology*; D008239:Lysine / Q000032:analysis* / Q000235:genetics; D008861:Microsomes / Q000201:enzymology; D008969:Molecular Sequence Data; D010957:Plasmids; D011898:Ranidae / Q000235:genetics; D012689:Sequence Homology, Nucleic Acid; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics* / Q000302:isolation & purification; D014101:Torpedo / Q000235:genetics; D014981:Xenopus / Q000235:genetics
D000251:Adenosine Triphosphatases; D000254:Sodium-Potassium-Exchanging ATPase; D008239:Lysine