title: Four novel sequences in Drosophila melanogaster homologous to the auxiliary Para sodium channel subunit TipE.
abstract: TipE is an auxiliary subunit of the Drosophila Para sodium channel. Here we describe four sequences, TEH1-4, homologous to TipE in the Drosophila melanogaster genome, harboring all typical structures of both TipE and the beta-Subunit family of big-conductance Ca(2+)-activated potassium channels: short cytosolic N- and C-terminal stretches, two transmembrane domains, and a large extracellular loop with two disulfide bonds. Whereas TEH1 and TEH2 lack the TipE-specific extension in the extracellular loop, both TEH3 and TEH4 possess two extracellular EGF-like domains. A CNS-specific expression was found for TEH1, while TEH2-4 were more widely expressed. The genes for TEH2-4 are localized close to the tipE gene on chromosome 3L. Coexpression of TEH subunits with Para in Xenopus oocytes showed a strong (30-fold, TEH1), medium (5- to 10-fold, TEH2 and TEH3), or no (TEH4) increase in sodium current amplitude, while TipE increased the current 20-fold. In addition, steady-state inactivation and the recovery from fast inactivation were altered by coexpression of Para with TEH1. We conclude that members of the TEH-family are auxiliary subunits for Para sodium channels and possibly other ion channels.
authors.affiliation: Center for Anatomy, Charité Berlin, Philippstr. 12, 10115 Berlin, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Derst
authors.forename: Christian
authors.initials: C
authors.lastname: Walther
authors.forename: Rüdiger W
authors.initials: RW
authors.lastname: Veh
authors.forename: Dieter
authors.initials: D
authors.lastname: Wicher
authors.forename: Stefan H
authors.initials: SH
authors.lastname: Heinemann
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002874:Chromosome Mapping; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics* / Q000378:metabolism*; D015640:Ion Channel Gating / Q000502:physiology; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D015222:Sodium Channels / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; D008565:Membrane Proteins; D015222:Sodium Channels; C586324:TEH1 protein, Drosophila; C000603759:TEH4 protein, Drosophila; C095833:TipE protein, Drosophila; C469950:para protein, Drosophila