Targeting of Vacuolar Membrane Localized Members of the TPK Channel Family
a Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute, University of Würzburg, Julius-von-Sachs-Platz 2, 97082 Würzburg, Germany
b Heidelberger Institut für Pflanzenwissenschaften (HIP), University of Heidelberg, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany (K.S.)
c Present address: Physiological Ecology of Plants, University of Tübingen, Auf der Morgenstelle 1, 72076 Tübingen, Germany
1 To whom correspondence should be addressed at the Department of Molecular Plant Physiology and Biophysics. E-mail hedrich{at}botanik.uni-wuerzburg.de, fax +49 (0)931/888-6157, tel. +49 (0)931/888-6100.
Four members of the tandem-pore potassium channel family of Arabidopsis thaliana (TPK1, 2, 3, and 5) reside in the vacuolar membrane, whereas TPK4 is a plasma membrane K+-channel. By constructing chimeras between TPK1 and TPK4, we attempted to identify channel domains involved in the trafficking process and found that the TPK1 cytoplasmic C-terminal domain (CT) is critical for the ER- as well as Golgi-sorting steps. Following site-directed mutagenesis, we identified a diacidic motif (DLE) required for ER-export of TPK1. However, this diacidic motif in the C-terminus is not conserved among other members of the TPK family, and TPK3 sorting is independent of its CT. Moreover, the 14-3-3 binding site of TPK1, essential for channel activation, is not involved in channel sorting.