Biochem Biophys Res Commun 2006 Jan 20;3393:939-48. doi: 10.1016/j.bbrc.2005.11.096.

Four novel sequences in Drosophila melanogaster homologous to the auxiliary Para sodium channel subunit TipE.

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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.

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Species referenced: Xenopus
Genes referenced: egf