Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Comparative Study
. 2004 Nov 16;101(46):16379-84.
doi: 10.1073/pnas.0407392101. Epub 2004 Nov 8.

Activation of Arp2/3 complex-dependent actin polymerization by plant proteins distantly related to Scar/WAVE

Mary Frank  1 , Coumaran Egile, Julia Dyachok, Stevan Djakovic, Michelle Nolasco, Rong Li, Laurie G Smith
Affiliations
Comparative Study

Activation of Arp2/3 complex-dependent actin polymerization by plant proteins distantly related to Scar/WAVE

Mary Frank et al. Proc Natl Acad Sci U S A. .

Abstract

The Arp2/3 complex, a highly conserved nucleator of F-actin polymerization, plays a key role in the regulation of actin dynamics eukaryotic cells. In animal cells and yeasts, Wiskott-Aldrich Syndrome protein (WASP)/suppressor of cAMP receptor (Scar)/WASP family verprolin homologous (WAVE) family proteins activate the Arp2/3 complex in response to localized cues. Like other eukaryotes, plants have an Arp2/3 complex, which has recently been shown to play an important role in F-actin organization and cell morphogenesis. However, no activators of the Arp2/3 complex have been identified in plants, which lack obvious homologs of WASP/Scar/WAVE family proteins. Here, we identify a family of Scar/WAVE-related plant Arp2/3 activators. Like Scar/WAVE proteins, four proteins identified in Arabidopsis thaliana (AtSCAR1 to AtSCAR4) and one in maize (ZmSCAR1) have a C-terminal WASP homology 2 (WH2)/acidic (WA)-verprolin homology/cofilin homology/acidic (VCA)-like domain, which we show can activate the bovine Arp2/3 complex. At their N termini, AtSCAR1 to ATSCAR4, along with a fifth protein lacking a VCA/WA-like domain at its C terminus (At4g18600), are related to the N-terminal Scar homology domains of Scar/WAVE family proteins. Analysis of gene expression patterns suggests functional redundancy among members of the AtSCAR family. Full-length AtSCAR1 and ATSCAR3 proteins and their Scar homology domains bind in vitro to AtBRICK 1 (AtBRK1), the Arabidopsis homolog of HSPC300, a WAVE-binding protein recently identified as a component of a complex implicated in the regulation of Scar/WAVE activity. Thus, AtSCAR proteins are likely to function in association with AtBRK1, and perhaps other Arabidopsis homologs of WAVE complex components, to regulate activation of the Arp2,3 complex in vivo.

PubMed Disclaimer

Figures

Fig. 4.
Fig. 4.
Binding interactions between AtSCAR proteins and AtBRK1 in vitro. AtSCAR3 (Left) or AtSCAR1 (Right) full-length proteins (A) or SHDs (B) were cotranscribed and translated with T7-tagged AtBRK1 (lanes 1 and 2 in each panel), T7-tagged negative control protein 2 (NC2; lanes 3 and 4), or T7-tagged negative control protein 1 (NC1; lanes 5 and 6). Inputs (I, 1/10th of total sample before anti-T7 bead incubation) are loaded in lanes 1, 3, and 5; proteins bound to anti-T7 beads (P, one-half of total sample) are loaded in lanes 2, 4, and 6.
Fig. 1.
Fig. 1.
Comparison of plant and animal Scar/WAVE proteins. (A) Schematic summary of the domain organization of mammalian WAVE1 (after ref. 29) and of AtSCAR proteins. B, basic region; PPPPP, polyproline-rich region; V, verprolin homology/WH2 motif; C, cofilin homology/connector region; A, acidic region. (B) Alignment of N termini of five SHD-containing Arabidopsis proteins: AtSCAR1 (At2g34150), AtSCAR2 (At2g38440), AtSCAR3 (At1g29170), AtSCAR4 (At5g01730), and At4g18600, with N termini of Scar/WAVE proteins from D. discoideum (AAD29083), C. elegans (NP_493028), D. melanogaster (NP_609477), and Mus musculus (NP_114083). (C) Alignment of C termini of the same proteins shown in B without At4g18600, which has no VCA-like region at its C terminus, but including Zea mays SCAR1 (BM340311). In B and C, domain boundaries are shown as defined previously (29). Asterisks mark residues that are invariant in animal Scar/WAVE proteins, including several not shown here. GenBank accession numbers for sequence-verified AtSCAR full-length coding regions are AY743923-AY743927.
Fig. 2.
Fig. 2.
Effect of AtSCARWA proteins on bovine Arp2/3 complex-dependent actin filament formation. (A) Nucleation activity was assessed by monitoring polymerization kinetics by using 1.5 μM actin (10% pyrene-labeled) and 10 nM bovine Arp2/3 complex. (B) Barbed end concentrations obtained at 50% polymerization with the indicated concentrations of GST-HsScarWA, GST-ZmSCAR1WA, and GST-AtSCAR3WA. (C) Like GST-HsScarWA, GST-ZmSCAR1WA promotes the formation of branched actin filaments. Actin filaments were polymerized in the presence of Arp2/3 complex and HsScarWA or ZmSCAR1WA, stained with AlexaFluor 488 phalloidin, and visualized by fluorescence microscopy.
Fig. 3.
Fig. 3.
RT-PCR analysis of the expression of AtSCAR1 to AtSCAR4 and At4g18600. Tissues analyzed (prepared as described in Materials and Methods) were flower buds (FB), expanding tip region of roots (ER), expanding siliques (ES), expanding cotyledons (EC), mature cotyledons (MC), expanding rosette leaves (EL), and mature rosette leaves (ML). RT, reverse transcriptase.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Pollard, T. D. & Borisy, G. G. (2003) Cell 112, 453-465. - PubMed
    1. Weaver, A. M., Young, M. E., Lee, W. L. & Cooper, J. A. (2003) Curr. Opin. Cell Biol. 15, 23-30. - PubMed
    1. Welch, M. D. & Mullins, R. D. (2002) Annu. Rev. Cell Dev. Biol. 18, 247-288. - PubMed
    1. Klahre, U. & Chua, N. H. (1999) Plant Mol. Biol. 41, 65-73. - PubMed
    1. Li, S., Blanchoin, L., Yang, Z. & Lord, E. M. (2003) Plant Physiol. 132, 2034-2044. - PMC - PubMed

Publication types

MeSH terms

LinkOut - more resources