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AtFim1 is an actin filament crosslinking protein from Arabidopsis thaliana
Author(s) -
Kovar David R.,
Staiger Christopher J.,
Weaver Eric A.,
McCurdy David W.
Publication year - 2000
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.2000.00907.x
Subject(s) - profilin , treadmilling , mdia1 , actin remodeling of neurons , actin remodeling , actin binding protein , biology , actin , microbiology and biotechnology , protein filament , microfilament , cytoskeleton , actin cytoskeleton , root hair , biophysics , biochemistry , gene , cell
Summary ATFIM1 is a widely expressed gene in Arabidopsis thaliana that encodes a putative actin filament‐crosslinking protein, AtFim1, belonging to the fimbrin/plastin class of actin‐binding proteins. In this report we have used bacterially expressed AtFim1 and actin isolated from Zea mays pollen to demonstrate that AtFim1 functions as an actin filament‐crosslinking protein. AtFim1 binds pollen actin filaments (F‐actin) in a calcium‐independent manner, with an average dissociation constant ( K d ) of 0.55 ± 0.21 µM and with a stoichiometry at saturation of 1 : 4 (mol AtFim1 : mol actin monomer). AtFim1 also crosslinks pollen F‐actin by a calcium‐independent mechanism, in contrast to crosslinking of plant actin by human T‐plastin, a known calcium‐sensitive actin‐crosslinking protein. When micro‐injected at high concentration into living Tradescantia virginiana stamen hair cells, AtFim1 caused cessation of both cytoplasmic streaming and transvacuolar strand dynamics within 2–4 min. Using the ‘nuclear displacement assay’ as a measure of the integrity of the actin cytoskeleton in living stamen hair cells, we demonstrated that AtFim1 protects actin filaments in these cells from Z. mays profilin (ZmPRO5)‐induced depolymerization, in a dose‐dependent manner. The apparent ability of AtFim1 to protect actin filaments in vivo from profilin‐mediated depolymerization was confirmed by in vitro sedimentation assays. Our results indicate that AtFim1 is a calcium‐independent, actin filament‐crosslinking protein that interacts with the actin cytoskeleton in living plant cells.