Structural basis of actin sequestration by thymosin-beta4: implications for WH2 proteins

EMBO J. 2004 Sep 15;23(18):3599-608. doi: 10.1038/sj.emboj.7600372. Epub 2004 Aug 26.


The WH2 (Wiscott-Aldridge syndrome protein homology domain 2) repeat is an actin interacting motif found in monomer sequestering and filament assembly proteins. We have stabilized the prototypical WH2 family member, thymosin-beta4 (Tbeta4), with respect to actin, by creating a hybrid between gelsolin domain 1 and the C-terminal half of Tbeta4 (G1-Tbeta4). This hybrid protein sequesters actin monomers, severs actin filaments and acts as a leaky barbed end cap. Here, we present the structure of the G1-Tbeta4:actin complex at 2 A resolution. The structure reveals that Tbeta4 sequesters by capping both ends of the actin monomer, and that exchange of actin between Tbeta4 and profilin is mediated by a minor overlap in binding sites. The structure implies that multiple WH2 motif-containing proteins will associate longitudinally with actin filaments. Finally, we discuss the role of the WH2 motif in arp2/3 activation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin-Related Protein 2
  • Actin-Related Protein 3
  • Actins / chemistry*
  • Actins / metabolism
  • Amino Acid Motifs
  • Amino Acid Sequence
  • Crystallography, X-Ray
  • Cytoskeletal Proteins / chemistry
  • Cytoskeleton / metabolism
  • Gelsolin / chemistry
  • Gelsolin / genetics
  • Gelsolin / metabolism
  • Humans
  • Molecular Sequence Data
  • Protein Binding
  • Protein Conformation
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism
  • Sequence Homology, Amino Acid
  • Thymosin / chemistry*
  • Thymosin / metabolism


  • ACTR2 protein, human
  • ACTR3 protein, human
  • Actin-Related Protein 2
  • Actin-Related Protein 3
  • Actins
  • Cytoskeletal Proteins
  • Gelsolin
  • Recombinant Fusion Proteins
  • thymosin beta(4)
  • Thymosin

Associated data

  • PDB/1T44