@article{HeldPascaudEckertetal.2011,
  author    = {Held, Katrin and Pascaud, Francois and Eckert, Christian and Gajdanowicz, Pawel and Hashimoto, Kenji and Corratge-Faillie, Claire and Offenborn, Jan Niklas and Lacombe, Benoit and Dreyer, Ingo and Thibaud, Jean-Baptiste and Kudla, J{\"o}rg},
  title     = {Calcium-dependent modulation and plasma membrane targeting of the AKT2 potassium channel by the CBL4/CIPK6 calcium sensor/protein kinase complex},
  series = {Cell research},
  volume    = {21},
  journal   = {Cell research},
  number    = {7},
  publisher = {Nature Publ. Group},
  address   = {Shanghai},
  issn      = {1001-0602},
  doi       = {10.1038/cr.2011.50},
  pages     = {1116 -- 1130},
  year      = {2011},
  abstract  = {Potassium (K(+)) channel function is fundamental to many physiological processes. However, components and mechanisms regulating the activity of plant K(+) channels remain poorly understood. Here, we show that the calcium (Ca(2+)) sensor CBL4 together with the interacting protein kinase CIPK6 modulates the activity and plasma membrane (PM) targeting of the K(+) channel AKT2 from Arabidopsis thaliana by mediating translocation of AKT2 to the PM in plant cells and enhancing AKT2 activity in oocytes. Accordingly, akt2, cbl4 and cipk6 mutants share similar developmental and delayed flowering phenotypes. Moreover, the isolated regulatory C-terminal domain of CIPK6 is sufficient for mediating CBL4- and Ca(2+)-dependent channel translocation from the endoplasmic reticulum membrane to the PM by a novel targeting pathway that is dependent on dual lipid modifications of CBL4 by myristoylation and palmitoylation. Thus, we describe a critical mechanism of ion-channel regulation where a Ca(2+) sensor modulates K(+) channel activity by promoting a kinase interaction-dependent but phosphorylation-independent translocation of the channel to the PM.},
  language  = {en}
}
@article{JohanssonWulfetangePoreeetal.2006,
  author    = {Johansson, Ingela and Wulfetange, Klaas and Poree, Fabien and Michard, Erwan and Gajdanowicz, Pawel and Lacombe, Benoit and Sentenac, Herve and Thibaud, Jean-Baptiste and M{\"u}ller-R{\"o}ber, Bernd and Blatt, Michael R. and Dreyer, Ingo},
  title     = {External K+ modulates the activity of the Arabidopsis potassium channel SKOR via an unusual mechanism},
  issn      = {0960-7412},
  doi       = {10.1111/j.1365-313X.2006.02690.X},
  year      = {2006},
  abstract  = {Plant outward-rectifying K+ channels mediate K+ efflux from guard cells during stomatal closure and from root cells into the xylem for root-shoot allocation of potassium (K). Intriguingly, the gating of these channels depends on the extracellular K+ concentration, although the ions carrying the current are derived from inside the cell. This K+ dependence confers a sensitivity to the extracellular K+ concentration ([K+]) that ensures that the channels mediate K+ efflux only, regardless of the [K+] prevailing outside. We investigated the mechanism of K+-dependent gating of the K+ channel SKOR of Arabidopsis by site-directed mutagenesis. Mutations affecting the intrinsic K+ dependence of gating were found to cluster in the pore and within the sixth transmembrane helix (S6), identifying an 'S6 gating domain' deep within the membrane. Mapping the SKOR sequence to the crystal structure of the voltage-dependent K+ channel KvAP from Aeropyrum pernix suggested interaction between the S6 gating domain and the base of the pore helix, a prediction supported by mutations at this site. These results offer a unique insight into the molecular basis for a physiologically important K+-sensory process in plants},
  language  = {en}
}
@article{MichardLacombePoreeetal.2005,
  author    = {Michard, Erwan and Lacombe, Beno{\^i}t and Poree, Fabien and M{\"u}ller-R{\"o}ber, Bernd and Sentenac, Herv{\´e} and Thibaud, Jean-Baptiste and Dreyer, Ingo},
  title     = {A unique voltage sensor sensitizes the potassium channel AKT2 to phosphoregulation},
  year      = {2005},
  abstract  = {Among all voltage-gated K+ channels from the model plant Arabidopsis thaliana, the weakly rectifying K+ channel (K-weak channel) AKT2 displays unique gating properties. AKT2 is exceptionally regulated by phosphorylation: when nonphosphorylated AKT2 behaves as an inward-rectifying potassium channel; phosphorylation of AKT2 abolishes inward rectification by shifting its activation threshold far positive (>200 mV) so that it closes only at voltages positive of + 100 mV. In its phosphorylated form, AKT2 is thus locked in the open state in the entire physiological voltage range. To understand the molecular grounds of this unique gating behavior, we generated chimeras between AKT2 and the conventional inward-rectifying channel KAT1. The transfer of the pore from KAT1 to AKT2 altered the permeation properties of the channel. However, the gating properties were unaffected, suggesting that the pore region of AKT2 is not responsible for the unique K-weak gating. Instead, a lysine residue in S4, highly conserved among all K-weak channels but absent from other plant K+ channels, was pinpointed in a site-directed mutagenesis approach. Substitution of the lysine by serine or aspartate abolished the "open-lock" characteristic and converted AKT2 into an inward- rectifying channel. Interestingly, phosphoregulation of the mutant AKT2-K197S appeared to be similar to that of the K-in channel KAT1: as suggested by mimicking the phosphorylated and dephosphorylated states, phosphorylation induced a shift of the activation threshold of AKT2-K197S by about +50 mV. We conclude that the lysine residue K197 sensitizes AKT2 to phosphoregulation. The phosphorylation-induced reduction of the activation energy in AKT2 is similar to 6 kT larger than in the K197S mutant. It is discussed that this hypersensitive response of AKT2 to phosphorylation equips a cell with the versatility to establish a potassium gradient and to make efficient use of it},
  language  = {en}
}