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Plant Cell. 2017 Oct;29(10):2570-2580. doi: 10.1105/tpc.17.00375. Epub 2017 Sep 29.

Fusicoccin Activates KAT1 Channels by Stabilizing Their Interaction with 14-3-3 Proteins.

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Department of Biosciences, University of Milan, 20133 Milan, Italy.
Plant Membrane Biophysics, Technical University Darmstadt, 64287 Darmstadt, Germany.
Department of Biosciences, University of Milan, 20133 Milan, Italy
Institute for Biophysics-Milan, Consiglio Nazionale delle Ricerche, 20133 Milan, Italy.


Plants acquire potassium (K+) ions for cell growth and movement via regulated diffusion through K+ channels. Here, we present crystallographic and functional data showing that the K+ inward rectifier KAT1 (K+Arabidopsis thaliana 1) channel is regulated by 14-3-3 proteins and further modulated by the phytotoxin fusicoccin, in analogy to the H+-ATPase. We identified a 14-3-3 mode III binding site at the very C terminus of KAT1 and cocrystallized it with tobacco (Nicotiana tabacum) 14-3-3 proteins to describe the protein complex at atomic detail. Validation of this interaction by electrophysiology shows that 14-3-3 binding augments KAT1 conductance by increasing the maximal current and by positively shifting the voltage dependency of gating. Fusicoccin potentiates the 14-3-3 effect on KAT1 activity by stabilizing their interaction. Crystal structure of the ternary complex reveals a noncanonical binding site for the toxin that adopts a novel conformation. The structural insights underscore the adaptability of fusicoccin, predicting more potential targets than so far anticipated. The data further advocate a common mechanism of regulation of the proton pump and a potassium channel, two essential elements in K+ uptake in plant cells.

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