The Ca2+/calmodulin binding domain of the Ca2+-ATPase linked to the Na+,K+-ATPase alters transport stoichiometry.
Using Xenopus oocytes as an expression system, we have investigated ion-transport and ouabain-binding properties of a chimeric ATPase (alpha1-CBD; Ishii and Takeyasu (1995) EMBO J. 14, 58-67) formed by the alpha1-subunit of chicken Na+,K(+)-ATPase (alpha1) and the calmodulin binding domain (CBD) of the rat plasma membrane Ca2(+)-ATPase. alpha1-CBD can be expressed and transported to the oocyte plasma membrane without the beta-subunit, and shows ouabain binding. In contrast to ouabain binding, this chimera requires the beta-subunit for its cation (Na+ and K+) transport activity. alpha1-CBD exhibits an altered stoichiometry of Na(+)-K+ exchange. A detailed analysis of 22Na+ efflux, 86Rb+ uptake, pump current and ouabain binding suggests that the chimeric molecule can operate in an electrically silent 2Na(+)-2K+ exchange mode and, with much lower probability, in its normal 3Na(+)-2K+ exchange mode.
Zhao
J
J
Max-Planck Institut für Biophysik, Frankfurt/Main, Germany.
Vasilets
L A
LA
Yoshimura
S H
SH
Gu
Q
Q
Ishii
T
T
Takeyasu
K
K
Schwarz
W
W
D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D002645:Chickens; D005260:Female; D007700:Kinetics; D008564:Membrane Potentials; D009865:Oocytes / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D014982:Xenopus laevis
D002147:Calmodulin; D011993:Recombinant Fusion Proteins; D010042:Ouabain; D012964:Sodium; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D002118:Calcium