Abstract
Fimbrins/plastins have been implicated in the generation of distinct actin structures, which are linked to different cellular processes. Historically, fimbrins/plastins were mainly considered as generating tight actin bundles. Here, we demonstrate that different members of the fimbrin/plastin family have diverged biochemically during evolution to generate either tight actin bundles or loose networks with distinct biochemical and biophysical properties. Using the phylogenetically and functionally distinct Arabidopsis fimbrins FIM4 and FIM5 we found that FIM4 generates both actin bundles and cross-linked actin filaments, whereas FIM5 only generates actin bundles. The distinct functions of FIM4 and FIM5 are clearly observed at single-filament resolution. Domain swapping experiments showed that cooperation between the conformationally plastic calponin-homology domain 2 (CH2) and the N-terminal headpiece determines the function of the full-length protein. Our study suggests that the structural plasticity of fimbrins/plastins has biologically meaningful consequences, and provides novel insights into the structure-function relationship of fimbrins/plastins as well as shedding light on how cells generate distinct actin structures.
Highlights
The actin cytoskeleton has been implicated in numerous fundamental physiological cellular processes, including cell migration, cell division, cytokinesis, intracellular trafficking, and so on [1, 2]
We found that the ability of recombinant FIMs (Fig. 1A) to generate higher-order actin structures mostly correlates with their phylogenetic grouping, as judged by the results of both low speed filamentous actin (F-actin) cosedimentation assays (Fig. 1B and supplemental Fig. S1B) and fluorescence light microscopy (Fig. 1C)
We demonstrate that fimbrins/plastins are able to generate loose actin networks besides their expected role in generating tight actin bundles
Summary
The actin cytoskeleton has been implicated in numerous fundamental physiological cellular processes, including cell migration, cell division, cytokinesis, intracellular trafficking, and so on [1, 2]. Initial observations showed that two Arabidopsis fimbrins, FIM1 and FIM5, are able to generate higher-order actin structures that probably have distinct morphology [27, 40], no side-by-side comparison was performed.
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