14-3-3 proteins double the number of outward-rectifying K+ channels available for activation in tomato cells
1999
Booij, P.P. | Roberts, M.R. | Vogelzang, S.A. | Kraayenhof, R. | Boer, A.H. de
Outward-rectifying K(+) channels are modulated in response to environmental stimuli by a range of intracellular factors, such as cytoplasmic Ca(2+), pH, kinases and phosphatases. Here we report that voltage-dependent outward-rectifying K(+) channels in tomato cells are also targets for modulation by 14-3-3 proteins. In whole-cell patch-clamp experiments, recombinant 14-3-3 protein (tomato isoform TFT7) was introduced into tomato cell protoplasts via the patch pipette. As a result the steady-state outward K(+) current increased twofold and this increase was not dependent upon the presence of cytoplasmic ATP. A phosphorylated peptide that contained a phosphorylated 14-3-3 target-binding motif (RSTS*TP), derived from nitrate reductase, blocked the effect of 14-3-3, thus showing the specific nature of 14-3-3 action. Kinetic parameters of the conductance, like (de)activation kinetics, voltage dependence of gating and activation potential, were not significantly different between control and 14-3-3 infused cells. Analysis of single-channel activity and whole-cell noise indicated that the single-channel conductance was not affected by 14-3-3 infusion. We conclude that 14-3-3 proteins recruit 'sleepy' channels into a voltage-activatable state. The molecular mechanism underlying the 1:1 ratio of constitutively active and 14-3-3 recruited channels is discussed in the light of known functions of 14-3-3 dimers.
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