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JXB Advance Access published online on September 12, 2006
Journal of Experimental Botany, doi:10.1093/jxb/erl104
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© The Author [2006]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org
Received February 20, 2006
Accepted June 28, 2006

RESEARCH PAPER

Phosphorylation of SPICK2, an AKT2 channel homologue from Samanea motor cells

Ling Yu 1 *, Dirk Becker 2 *, Hadas Levi 1, Menachem Moshelion 1, Rainer Hedrich 2, Ilana Lotan 3, Arie Moran 4, Uri Pick 5, Leah Naveh 1, Yael Libal 1, and Nava Moran 1 *

1 The Robert H. Smith Institute for Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, Food and Environmental Quality Sciences, the Hebrew University of Jerusalem, Rehovot 76100, Israel
2 Julius-von-Sachs-Insitute, Department of Botany I: Molecular Plant Physiology and Biophysics, University of Wuerzburg, Julius-von-Sachs-Platz 2, D-97082 Wuerzburg, Germany
3 Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel
4 Department of Physiology, Faculty of Health Sciences, Ben-Gurion University, Beer Sheva, Israel
5 Department of Biological Chemistry, Weizmann Instititute of Science, Rehovot 76100, Israel

* To whom correspondence should be addressed.
Nava Moran, E-mail: nava.moran{at}huji.ac.il


  Abstract

SPICK2, a homologue of the weakly-inward-rectifying Shaker-like Arabidopsis K channel, AKT2, is a candidate K+-influx channel participating in light- and clock-regulated leaf movements of the legume, Samanea saman. Light and the biological clock regulate the in situ K+-influx channel activity differentially in extensor and flexor halves of the pulvinus (the S. saman leaf motor organ), and also--though differently--the transcript level of SPICK2 in the pulvinus. This disparity between the in situ channel activity versus its candidate transcript, along with the sequence analysis of SPICK2, suggest an in situ regulation of the activity of SPICK2, possibly by phosphorylation and/or by interaction with cAMP. Consistent with this (i) the activity of the voltage-dependent K+-selective fraction of the inward current in extensor and flexor cells was affected differentially in whole-cell patch-clamp assays promoting phosphorylation (using the protein phosphatase inhibitor okadaic acid); (ii) several proteins in isolated plasma membrane-enriched vesicles of the motor cells underwent phosphorylation without an added kinase in conditions similar to patch-clamp; and (iii) the SPICK2 protein was phosphorylated in vitro by the catalytic subunit of the broad-range cAMP-dependent protein kinase. All of these results are consistent with the notion that SPICK2 is the K+-influx channel, and is regulated in vivo directly by phosphorylation.

Keywords: AKT2; gating; kinase; motor cells; nucleotides; phosphorylation; PKA; potassium channel; selectivity; Samanea.

*These authors contributed equally to this work.


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