TY - JOUR A1 - Fischer, Florian A1 - Räder, Andy A1 - Wewetzer, Gudrun A1 - Hempel, Luisa A1 - Sack, Beate A1 - Schwill, Andreas A1 - Surrey, Heike A1 - Claussen, Martin A1 - Klein, Oliver A1 - Czempinski, Katrin A1 - Küchmeister, Heike A1 - González, Antonio Martínez A1 - Pecher, Klaus A1 - Resch-Esser, Ursula A1 - Gommert, Natalie T1 - Portal = Unbekanntes Terrain: Die EU-Erweiterung birgt neue Möglichkeiten BT - Die Potsdamer Universitätszeitung N2 - Aus dem Inhalt: - Unbekanntes Terrain: Die EU-Erweiterung birgt neue Möglichkeiten - Zehn Jahre MenschenRechtsZentrum - Wassermangel im Nahen Osten - Karl-Scheel-Preis für Turbulenzforschung T3 - Portal: Das Potsdamer Universitätsmagazin - 06-08/2004 Y1 - 2004 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-439806 SN - 1618-6893 IS - 06-08/2004 ER - TY - JOUR A1 - Becker, Dirk A1 - Geiger, D. A1 - Dunkel, M. A1 - Roller, A. A1 - Bertl, Adam A1 - Latz, A. A1 - Carpaneto, Armando A1 - Dietrich, Peter A1 - Roelfsema, M. R. G. A1 - Voelker, C. A1 - Schmidt, D. A1 - Müller-Röber, Bernd A1 - Czempinski, Katrin A1 - Hedrich, R. T1 - AtTPK4, an Arabidopsis tandem-pore K+ channel, poised to control the pollen membrane voltage in a pH- and Ca2+- dependent manner N2 - 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 Y1 - 2004 SN - 0027-8424 ER - TY - JOUR A1 - Bihler, Hermann A1 - Eing, C. A1 - Hebeisen, S. A1 - Roller, A. A1 - Czempinski, Katrin A1 - Bertl, Adam T1 - TPK1 is a vacuolar ion channel different from the slow-vacuolar cation channel N2 - 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 Y1 - 2005 ER - TY - JOUR A1 - Voelker, Camilla A1 - Gomez-Porras, Judith Lucia A1 - Becker, Dirk A1 - Hamamoto, Shin A1 - Uozumi, Nobuyuki A1 - Gambale, Franco A1 - Müller-Röber, Bernd A1 - Czempinski, Katrin A1 - Dreyer, Ingo T1 - Roles of tandem-pore K plus channels in plants : a puzzle still to be solved N2 - The group of voltage-independent K+ channels in Arabidopsis thaliana consists of six members, five tandem-pore channels (TPK1-TPK5) and a single K-ir-like channel (KCO3). All TPK/KCO channels are located at the vacuolar membrane except for TPK4, which was shown to be a plasma membrane channel in pollen. The vacuolar channels interact with 14-3-3 proteins (also called General Regulating Factors, GRFs), indicating regulation at the level of protein-protein interactions. Here we review current knowledge about these ion channels and their genes, and highlight open questions that need to be urgently addressed in future studies to fully appreciate the physiological functions of these ion channels. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=1435-8603 U6 - https://doi.org/10.1111/j.1438-8677.2010.00353.x SN - 1435-8603 ER - TY - JOUR A1 - Maitrejean, Marie A1 - Wudick, Michael M. A1 - Völker, Camilla A1 - Prinsi, Bhakti A1 - Müller-Röber, Bernd A1 - Czempinski, Katrin A1 - Pedrazzini, Emanuela A1 - Vitale, Alessandro T1 - Assembly and sorting of the tonoplast potassium channel AtTPK1 and its turnover by internalization into the Vacuole JF - Plant physiology : an international journal devoted to physiology, biochemistry, cellular and molecular biology, biophysics and environmental biology of plants N2 - The assembly, sorting signals, and turnover of the tonoplast potassium channel AtTPK1 of Arabidopsis (Arabidopsis thaliana) were studied. We used transgenic Arabidopsis expressing a TPK1-green fluorescent protein (GFP) fusion or protoplasts transiently transformed with chimeric constructs based on domain exchange between TPK1 and TPK4, the only TPK family member not located at the tonoplast. The results show that TPK1-GFP is a dimer and that the newly synthesized polypeptides transiently interact with a thus-far unidentified 20-kD polypeptide. A subset of the TPK1-TPK4 chimeras were unable to assemble correctly and these remained located in the endoplasmic reticulum where they interacted with the binding protein chaperone. Therefore, TPK1 must assemble correctly to pass endoplasmic reticulum quality control. Substitution of the cytosolic C terminus of TPK4 with the corresponding domain of TPK1 was sufficient to allow tonoplast delivery, indicating that this domain contains tonoplast sorting information. Pulse-chase labeling indicated that TPK1-GFP has a half-life of at least 24 h. Turnover of the fusion protein involves internalization into the vacuole where the GFP domain is released. This indicates a possible mechanism for the turnover of tonoplast proteins. Y1 - 2011 U6 - https://doi.org/10.1104/pp.111.177816 SN - 0032-0889 VL - 156 IS - 4 SP - 1783 EP - 1796 PB - American Society of Plant Physiologists CY - Rockville ER - TY - JOUR A1 - Rocchetti, Alessandra A1 - Sharma, Tripti A1 - Wulfetange, Camilla A1 - Scholz-Starke, Joachim A1 - Grippa, Alexandra A1 - Carpaneto, Armando A1 - Dreyer, Ingo A1 - Vitale, Alessandro A1 - Czempinski, Katrin A1 - Pedrazzini, Emanuela T1 - The putative K+ channel subunit AtKCO3 forms stable dimers in arabidopsis JF - Frontiers in plant science N2 - The permeation pore of K+ channels is formed by four copies of the pore domain. AtKCO3 is the only putative voltage-independent K+ channel subunit of Arabidopsis thaliana with a single pore domain. KCO3-like proteins recently emerged in evolution and, to date, have been found only in the genus Arabidopsis (A. thaliana and A. lyrata). We show that the absence of KCO3 does not cause marked changes in growth under various conditions. Only under osmotic stress we observed reduced root growth of the kco3-1 null-allele line. This phenotype was complemented by expressing a KCO3 mutant with an inactive pore, indicating that the function of KCO3 under osmotic stress does not depend on its direct ability to transport ions. Constitutively overexpressed AtKCO3 or AtKCO3::G FP are efficiently sorted to the tonoplast indicating that the protein is approved by the endoplasmic reticulum quality control. However, vacuoles isolated from transgenic plants do not have significant alterations in current density. Consistently, both AtKCO3 and AtKCO3::GFP are detected as homodimers upon velocity gradient centrifugation, an assembly state that would not allow for activity. We conclude that if AtKCO3 ever functions as a K+ channel, active tetramers are held by particularly weak interactions, are formed only in unknown specific conditions and may require partner proteins. KW - Arabidopsis KW - membrane proteins KW - potassium channels KW - protein assembly KW - tonoplast Y1 - 2012 U6 - https://doi.org/10.3389/fpls.2012.00251 SN - 1664-462X VL - 3 PB - Frontiers Research Foundation CY - Lausanne ER -