title: Probing the transmembrane topology of cyclic nucleotide-gated ion channels with a gene fusion approach.
abstract: Cyclic nucleotide-gated (CNG) cation channels contain two short sequence motifs--a residual voltage-sensor (S4) and a pore-forming (P) segment--that are reminiscent of similar segments in voltage-activated Shaker-type K+ channels. It has been tacitly assumed that CNG channels and this K+ channel subfamily share a common overall topology, characterized by a hydrophobic domain comprising six membrane-spanning segments. We have systematically investigated the topology of CNG channels from bovine rod photoreceptor and Drosophila melanogaster by a gene fusion approach using the bacterial reporter enzymes alkaline phosphatase and beta-galactosidase, which are active only in the periplasm and only in the cytoplasm, respectively. Enzymatic activity was determined after expression of fusion constructs in Escherichia coli. CNG channels were found to have six membrane-spanning segments, suggesting that CNG and Shaker-type K+ channels, albeit distant relatives within a gene superfamily of ion channels, share a common topology.
authors.affiliation: Institut für Biologische Informationsverarbeitung, Forschungszentrum Jülich, Germany.
authors.forename: D K
authors.initials: DK
authors.lastname: Henn
authors.forename: A
authors.initials: A
authors.lastname: Baumann
authors.forename: U B
authors.initials: UB
authors.lastname: Kaupp
mesh_terms: D000469:Alkaline Phosphatase / Q000235:genetics; D000818:Animals; D002417:Cattle; D003001:Cloning, Molecular; D054815:Cyclic Nucleotide-Gated Cation Channels; D018076:DNA, Complementary / Q000235:genetics; D004331:Drosophila melanogaster; D004926:Escherichia coli / Q000235:genetics; D017930:Genes, Reporter; D015640:Ion Channel Gating / Q000235:genetics; D007473:Ion Channels / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009712:Nucleotides, Cyclic / Q000378:metabolism*; D017956:Photoreceptor Cells, Invertebrate / Q000378:metabolism; D001616:beta-Galactosidase / Q000235:genetics
chemical_list: D054815:Cyclic Nucleotide-Gated Cation Channels; D018076:DNA, Complementary; D007473:Ion Channels; D009712:Nucleotides, Cyclic; D000469:Alkaline Phosphatase; D001616:beta-Galactosidase