Distinct roles of the last transmembrane domain in controlling Arabidopsis K super(+) channel activity

* times The family of voltage-gated potassium channels in plants presumably evolved from a common ancestor and includes both inward-rectifying (K sub(in)) channels that allow plant cells to accumulate K super(+) and outward-rectifying (K sub(out)) channels that mediate K super(+) efflux. Despite their close structural similarities, the activity of K sub(in) channels is largely independent of K super(+) and depends only on the transmembrane voltage, whereas that of K sub(out) channels responds to the membrane voltage and the prevailing extracellular K super(+) concentration. Gating of potassium channels is achieved by structural rearrangements within the last transmembrane domain (S6). * times Here we investigated the functional equivalence of the S6 helices of the K sub(in) channel KAT1 and the K sub(out) channel SKOR by domain-swapping and site-directed mutagenesis. Channel mutants and chimeras were analyzed after expression in Xenopus oocytes. * times We identified two discrete regions that influence gating differently in both channels, demonstrating a lack of functional complementarity between KAT1 and SKOR. Our findings are supported by molecular models of KAT1 and SKOR in the open and closed states. * times The role of the S6 segment in gating evolved differently during specialization of the two channel subclasses, posing an obstacle for the transfer of the K super(+)-sensor from K sub(out) to K sub(in) channels.