@article{PoreeWulfetangeNasoetal.2005,
  author    = {Poree, Fabien and Wulfetange, K. and Naso, A. and Carpaneto, Armando and Roller, A. and Natura, G. and Bertl, Adam and Sentenac, H. and Thibaud, Jean-Baptiste and Dreyer, Ingo},
  title     = {Plant K-in and K-out channels : Approaching the trait of opposite rectification by analyzing more than 250 KAT1- SKOR chimeras},
  issn      = {0006-291X},
  year      = {2005},
  abstract  = {Members of the Shaker-like plant K+ channel family share a common structure, but are highly diverse in their function: they behave as either hyperpolarization-activated inward-rectifying (K-in) channels, or leak-like (K-weak) channels, or depolarization-activated outward-rectifying (K-out) channels. Here we created 256 chimeras between the K-in channel KAT1 and the K-out channel SKOR. The chimeras were screened in a potassium-uptake deficient yeast strain to identify those, which mediate potassium inward currents, i.e., which are functionally equivalent to KAT1. This strategy allowed Lis to identify three chimeras which differ from KAT1 in three parts of the polypeptide: the cytosolic N- terminus, the cytosolic C-terminus, and the putative voltage-sensor S4. Additionally, mutations in the K-out Channel SKOR were generated in order to localize molecular entities underlying its depolarization activation. The triple mutant SKOR-D312N-M313L-1314G, carrying amino-acid changes in the S6 segment, was identified as a channel which did not display any rectification in the tested voltage-range. (C) 2005 Elsevier Inc. All rights reserved},
  language  = {en}
}
@article{BihlerEingHebeisenetal.2005,
  author    = {Bihler, Hermann and Eing, C. and Hebeisen, S. and Roller, A. and Czempinski, Katrin and Bertl, Adam},
  title     = {TPK1 is a vacuolar ion channel different from the slow-vacuolar cation channel},
  year      = {2005},
  abstract  = {TPK1 ( formerly KCO1) is the founding member of the family of two-pore domain K 1 channels in Arabidopsis ( Arabidopsis thaliana), which originally was described following expression in Sf9 insect cells as a Ca2(+)- and voltage- dependent outwardly rectifying plasma membrane K 1 channel. In plants, this channel has been shown by green fluorescent protein fusion to localize to the vacuolar membrane, which led to speculations that the TPK1 gene product would be a component of the nonselective, Ca2+ and voltage- dependent slow-vacuolar (SV) cation channel found in many plants species. Using yeast ( Saccharomyces cerevisiae) as an expression system for TPK1, we show functional expression of the channel in the vacuolar membrane. In isolated vacuoles of yeast yvc1 disruption mutants, the TPK1 gene product shows ion channel activity with some characteristics very similar to the SV-type channel. The open channel conductance of TPK1 in symmetrically 100mM KCl is slightly asymmetric with roughly 40 pS at positive membrane voltages and 75 pS at negative voltages. Similar to the SV-type channel, TPK1 is activated by cytosolic Ca2+, requiring micromolar concentration for activation. However, in contrast to the SV- type channel, TPK1 exhibits strong selectivity for K+ over Na+, and its activity turned out to be independent of the membrane voltage over the range of +/- 80mV. Our data clearly demonstrate that TPK1 is a voltage- independent, Ca2+- activated, K+- selective ion channel in the vacuolar membrane that does not mediate SV- type ionic currents},
  language  = {en}
}
@article{DreyerPoreeSchneideretal.2004,
  author    = {Dreyer, Ingo and Poree, Fabien and Schneider, A. and Mittelstadt, J. and Bertl, Adam and Sentenac, H. and Thibaud, Jean-Baptiste and M{\"u}ller-R{\"o}ber, Bernd},
  title     = {Assembly of plant Shaker-like K-out channels requires two distinct sites of the channel alpha-subunit},
  issn      = {0006-3495},
  year      = {2004},
  abstract  = {SKOR and GORK are outward-rectifying plant potassium channels from Arabidopsis thaliana. They belong to the Shaker superfamily of voltage-dependent K+ channels. Channels of this class are composed of four alpha-subunits and subunit assembly is a prerequisite for channel function. In this study the assembly mechanism of SKOR was investigated using the yeast two-hybrid system and functional assays in Xenopus oocytes and in yeast. We demonstrate that SKOR and GORK physically interact and assemble into heteromeric K-out channels. Deletion mutants and chimeric proteins generated from SKOR and the K-in channel alpha-subunit KAT1 revealed that the cytoplasmic C-terminus of SKOR determines channel assembly. Two domains thatchannel a-subunit KAT1 revealed that the cytoplasmic C-terminus of SKOR determines channel assembly. Two domains that are crucial for channel assembly were identified: i), a proximal interacting region comprising a putative cyclic nucleotide-binding domain together with 33 amino acids just upstream of this domain, and ii), a distal interacting region showing some resemblance to the K-T domain of KAT1. Both regions contributed differently to channel assembly. Whereas the proximal interacting region was found to be active on its own, the distal interacting region required an intact proximal interacting region to be active. K-out alpha-subunits did not assemble with K-in alpha-subunits because of the absence of interaction between their assembly sites},
  language  = {en}
}
@article{BeckerGeigerDunkeletal.2004,
  author    = {Becker, Dirk and Geiger, D. and Dunkel, M. and Roller, A. and Bertl, Adam and Latz, A. and Carpaneto, Armando and Dietrich, Peter and Roelfsema, M. R. G. and Voelker, C. and Schmidt, D. and M{\"u}ller-R{\"o}ber, Bernd and Czempinski, Katrin and Hedrich, R.},
  title     = {AtTPK4, an Arabidopsis tandem-pore K+ channel, poised to control the pollen membrane voltage in a pH- and Ca2+- dependent manner},
  issn      = {0027-8424},
  year      = {2004},
  abstract  = {The Arabidopsis tandem-pore K+ (TPK) channels displaying four transmembrane domains and two pore regions share structural homologies with their animal counterparts of the KCNK family. In contrast to the Shaker-like Arabidopsis channels (six transmembrane domains/one pore region), the functional properties and the biological role of plant TPK channels have not been elucidated yet. Here, we show that AtTPK4 (KCO4) localizes to the plasma membrane and is predominantly expressed in pollen. AtTPK4 (KCO4) resembles the electrical properties of a voltage-independent K+ channel after expression in Xenopus oocytes and yeast. Hyperpolarizing as well as depolarizing membrane voltages elicited instantaneous K+ currents, which were blocked by extracellular calcium and cytoplasmic protons. Functional complementation assays using a K+ transport-deficient yeast confirmed the biophysical and pharmacological properties of the AtTPK4 channel. The features of AtTPK4 point toward a role in potassium homeostasis and membrane voltage control of the growing pollen tube. Thus, AtTPK4 represents a member of plant tandem-pore-K+ channels, resembling the characteristics of its animal counterparts as well as plant-specific features with respect to modulation of channel activity by acidosis and calcium},
  language  = {en}
}