AtFim1 is an actin filament crosslinking protein from Arabidopsis thaliana

Plant J. 2000 Dec;24(5):625-36. doi: 10.1046/j.1365-313x.2000.00907.x.


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 (Kd) of 0.55+/-0.21 microM 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Actins / metabolism
  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins*
  • Binding, Competitive
  • Calcium / pharmacology
  • Cross-Linking Reagents
  • DNA, Recombinant
  • Microfilament Proteins / metabolism*
  • Plant Cells
  • Plant Proteins / genetics
  • Plant Proteins / metabolism*
  • Plant Proteins / pharmacology
  • Plants / drug effects
  • Plants / metabolism
  • Pollen / chemistry
  • Protein Binding / drug effects


  • ATFIM1 protein, Arabidopsis
  • Actins
  • Arabidopsis Proteins
  • Cross-Linking Reagents
  • DNA, Recombinant
  • Microfilament Proteins
  • Plant Proteins
  • Calcium