Substitution of a single residue, Asp575, renders the NCKX2 K+-dependent Na+/Ca2+ exchanger independent of K+.
The Na(+)/Ca(2+)-K(+) exchanger (NCKX) is a polytopic membrane protein that uses both the inward Na(+) gradient and the outward K(+) gradient to drive Ca(2+) extrusion across the plasma membrane. NCKX1 is found in retinal rod photoreceptors, while NCKX2 is found in retinal cone photoreceptors and is also widely expressed in the brain. Here, we have identified a single residue (out of >100 tested) for which substitution removed the K(+) dependence of NCKX-mediated Ca(2+) transport. Charge-removing replacement of Asp(575) by either asparagine or cysteine rendered the mutant NCKX2 proteins independent of K(+), whereas the charge-conservative substitution of Asp(575) to glutamate resulted in a nonfunctional mutant NCKX2 protein, accentuating the critical nature of this residue. Asp(575) is conserved in the NCKX1-5 genes, while an asparagine is found in this position in the three NCX genes, coding for the K(+)-independent Na(+)/Ca(2+) exchanger.
Kang
Kyeong-Jin
KJ
Department of Physiology & Biophysics, Faculty of Medicine, Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta T2N 4N1, Canada.
Shibukawa
Yoshiyuki
Y
Szerencsei
Robert T
RT
Schnetkamp
Paul P M
PP
D019943:Amino Acid Substitution; D001216:Asparagine; D001224:Aspartic Acid; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D004594:Electrophysiology; D006801:Humans; D007700:Kinetics; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology*; D019831:Sodium-Calcium Exchanger / Q000235:genetics* / Q000502:physiology
D019831:Sodium-Calcium Exchanger; C074530:potassium-dependent sodium-calcium exchanger; D001224:Aspartic Acid; D001216:Asparagine; D011188:Potassium; D002118:Calcium