Chereau, D. et al. Actin-bound structures of Wiskott-Aldrich syndrome protein (WASP)-homology domain 2 and the implications for filament assembly. Proc. Natl Acad. Sci. USA 102, 16644-16649

Boston Biomedical Research Institute, Watertown, MA 02472, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 12/2005; 102(46):16644-9. DOI: 10.1073/pnas.0507021102
Source: PubMed


Wiskott-Aldrich syndrome protein (WASP)-homology domain 2 (WH2) is a small and widespread actin-binding motif. In the WASP family, WH2 plays a role in filament nucleation by Arp2/3 complex. Here we describe the crystal structures of complexes of actin with the WH2 domains of WASP, WASP-family verprolin homologous protein, and WASP-interacting protein. Despite low sequence identity, WH2 shares structural similarity with the N-terminal portion of the actin monomer-sequestering thymosin beta domain (Tbeta). We show that both domains inhibit nucleotide exchange by targeting the cleft between actin subdomains 1 and 3, a common binding site for many unrelated actin-binding proteins. Importantly, WH2 is significantly shorter than Tbeta but binds actin with approximately 10-fold higher affinity. WH2 lacks a C-terminal extension that in Tbeta4 becomes involved in monomer sequestration by interfering with intersubunit contacts in F-actin. Owing to their shorter length, WH2 domains connected in tandem by short linkers can coexist with intersubunit contacts in F-actin and are proposed to function in filament nucleation by lining up actin subunits along a filament strand. The WH2-central region of WASP-family proteins is proposed to function in an analogous way by forming a special class of tandem repeats whose function is to line up actin and Arp2 during Arp2/3 nucleation. The structures also suggest a mechanism for how profilin-binding Pro-rich sequences positioned N-terminal to WH2 could feed actin monomers directly to WH2, thereby playing a role in filament elongation.

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    • "The interactions of the LKKT(V) domain are for the most part electrostatic in character, with positively charged residues of the WH2 domain facing negatively charged residues on the actin surface (Chereau et al., 2005; Dominguez, 2007; Lee and Dominguez, 2010). Exportin-6 has the similar motif (LKPS) near residue 765, which corresponds to helix14A. "
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    • "Comparison with the WH2 Domain Many actin-binding proteins target the barbed-end groove occupied by helix aA of Bud6 flank (Dominguez, 2009). In particular, WH2 domains contain a helix that binds this site in a manner quite similar to Bud6 (Chereau et al., 2005). The actin monomer-sequestering protein b-thymosin also contains the WH2 motif and forms a similar interaction with actin (Dominguez, 2007). "
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    ABSTRACT: In budding yeast, the actin-binding protein Bud6 cooperates with formins Bni1 and Bnr1 to catalyze the assembly of actin filaments. The nucleation-enhancing activity of Bud6 requires both a "core" domain that binds to the formin and a "flank" domain that binds monomeric actin. Here, we describe the structure of the Bud6 flank domain in complex with actin. Two helices in Bud6(flank) interact with actin; one binds in a groove at the barbed end of the actin monomer in a manner closely resembling the helix of WH2 domains, a motif found in many actin nucleation factors. The second helix rises along the face of actin. Mutational analysis verifies the importance of these Bud6-actin contacts for nucleation-enhancing activity. The Bud6 binding site on actin overlaps with that of the formin FH2 domain and is also incompatible with inter-subunit contacts in F-actin, suggesting that Bud6 interacts only transiently with actin monomers during filament nucleation. Copyright © 2015 Elsevier Ltd. All rights reserved.
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    • "In cells actin treadmilling is enhanced by the combined nucleotide-dependent activities of ABPs (Didry et al., 1998; Renault et al., 2008). The formin family of proteins and the actin-related protein (Arp)2/3 complex machinery can catalyze the de novo assembly of actin filaments preferentially by binding to the ATP-bound actin units (Chereau et al., 2005; Ichetovkin et al., 2002; Romero et al., 2007). The disassembly of actin filaments can be enhanced by members of the ADF-H domain-containing ADF/cofilin proteins, which preferentially bind to the ADP-loaded regions of the filaments and accelerate the dissociation of actin subunits (Blanchoin and Pollard, 1999; Carlier et al., 1997; Suarez et al., 2011). "
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    ABSTRACT: Several cellular processes rely on the fine tuning of actin cytoskeleton. A central component in the regulation of this cellular machinery is the ADF-H domain proteins. Despite sharing the same domain, ADF-H domain proteins produce a diverse functional landscape in the regulation of the actin cytoskeleton. Recent findings emphasize that the functional and structural features of these proteins can differ not only between ADF-H families but even within the same family. The structural and evolutional background of this functional diversity is poorly understood. This review focuses on the specific functional characteristics of ADF-H domain proteins and how these features can be linked to structural differences in the ADF-H domain and also to different conformational transitions in actin. In the light of recent discoveries we pay special attention to the ADF/cofilin proteins to find tendencies along which the functional and structural diversification is governed through the evolution.
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