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Molecular and Cellular Biology, March 2007, p. 2144-2154, Vol. 27, No. 6
0270-7306/07/$08.00+0 doi:10.1128/MCB.02347-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
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Department of Plant Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel,1 Department of Field and Vegetable Crops, Agricultural Research Organization, Newe Ya'ar Reseach Center, P.O. Box 1021, Ramat Yishay 30095, Israel2
Received 17 December 2006/ Accepted 1 January 2007
ROPs
or RACs are plant Rho-related GTPases implicated in the regulation of
a multitude of signaling pathways that function at the
plasma membrane by virtue of posttranslational lipid modifications. The
relationship between ROP activation status and membrane localization
has not been established. Here we demonstrate that endogenous ROPs, as
well as a transgenic His6-green fluorescent protein
(GFP)-AtROP6 fusion protein, were partitioned between Triton
X-100-soluble and -insoluble membranes. In contrast, an activated
His6-GFP-Atrop6CA mutant protein accumulated
exclusively in detergent-resistant membranes. GDP induced accumulation
of ROPs in Triton-soluble membranes, whereas GTP
S induced
accumulation of ROPs in detergent-resistant membranes. Recombinant
wild-type and constitutively active AtROP6 isoforms were purified from
Arabidopsis plants, and their lipids were cleaved and analyzed
by gas chromatography-coupled mass spectrometry. In Triton-soluble
membranes, wild-type AtROP6 was only prenylated, primarily by
geranylgeranyl. The activated AtROP6 that accumulated in
detergent-resistant membranes was modified by prenyl and acyl lipids.
The acyl lipids were identified as palmitic and stearic acids. In
agreement, activated
His6-GFP-Atrop6CAmS156 in which
cysteine156 was mutated into serine accumulated in
Triton-soluble membranes. These findings show that upon GTP binding and
activation, AtROP6 and possibly other ROPs are transiently S acylated,
which induces their partitioning into detergent-resistant
membranes.
Published ahead of print on 22 January 2007.
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http://mcb.asm.org/.
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