title: Molecular cloning of a fourth member of the potassium-dependent sodium-calcium exchanger gene family, NCKX4.
abstract: We report here the identification and characterization of a fourth member of the potassium-dependent sodium-calcium exchanger gene family, NCKX4 (gene SLC24A4), which mapped to the chromosomal region 14q32. Human NCKX4 encoded a protein of 605 amino acids that displayed a high level of sequence identity to previously described family members, rod NCKX1 (gene SLC24A1), cone/neuronal NCKX2 (gene SLC24A2), and ubiquitous NCKX3 (gene SLC24A3), in the hydrophobic regions surrounding the alpha-repeat sequences thought to form the ion-binding pocket used for transport. The protein product of the NCKX4 gene shared the highest level of amino acid identity, as well as an almost identical arrangement of exon boundaries, with NCKX3, indicating that these two genes have arisen from a recent duplication event. NCKX4 transcripts were abundantly expressed in all brain regions, aorta, lung, and thymus, as well as at a lower level in many other tissues. The NCKX4 protein demonstrated potassium-dependent sodium calcium exchanger activity when assayed in transfected HEK293 cells using digital imaging of fura-2 fluorescence. The discovery of NCKX4, as far as can be ascertained from the current version of the human genome sequence, completes the mammalian potassium-dependent sodium-calcium exchanger gene family.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Calgary, Alberta T2N 4N1, Canada.
authors.forename: Xiao-Fang
authors.initials: XF
authors.lastname: Li
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Kraev
authors.forename: Jonathan
authors.initials: J
authors.lastname: Lytton
mesh_terms: D000595:Amino Acid Sequence; D017920:Antiporters / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D002460:Cell Line; D002874:Chromosome Mapping; D002883:Chromosomes, Human, Pair 14; D003001:Cloning, Molecular; D018076:DNA, Complementary; D050612:Fatty Acid Transport Proteins; D006801:Humans; D008969:Molecular Sequence Data; D011188:Potassium / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D017920:Antiporters; D018076:DNA, Complementary; D050612:Fatty Acid Transport Proteins; D012333:RNA, Messenger; C470570:SLC24A4 protein, human; C493572:Slc27a4 protein, mouse; D011188:Potassium