K+ transport characteristics of the plasma membrane tandem‐pore channel TPK4 and pore chimeras with its vacuolar homologs

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Abstract
Vacuolar tandem‐pore channels could not be analysed in Xenopus oocytes so far, due to misguided translocation. Owing to the conservation of their pore regions, we were able to prepare functional pore‐chimeras between the plasma membrane localised TPK4 and vacuolar TPKs. Thereby, we found evidence that TPK2, TPK3 and TPK5, just like TPK4, form potassium‐selective channels with instantaneous current kinetics. Homology modelling and mutational analyses identified a pore‐located aspartate residue (Asp110), which is involved in potassium permeation as well as in inward rectification of TPK4. Furthermore, dominant‐negative mutations in the selectivity filter of either pore one or two (Asp86, Asp200) rendered TPK4 non‐functional. This observation supports the notion that the functional TPK4 channel complex is formed by two subunits.

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