Structural basis of actin sequestration by thymosin-beta4: implications for WH2 proteins.
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.
Department of Medical Biochemistry and Microbiology, Uppsala Biomedical Center, Uppsala University, Uppsala, Sweden.
Edward
E
Irobi
Adeleke H
AH
Aguda
Mårten
M
Larsson
Christophe
C
Guerin
Helen L
HL
Yin
Leslie D
LD
Burtnick
Laurent
L
Blanchoin
Robert C
RC
Robinson
D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins / Q000737:chemistry* / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D003598:Cytoskeletal Proteins / Q000737:chemistry; D003599:Cytoskeleton / Q000378:metabolism; D018260:Gelsolin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013947:Thymosin / Q000737:chemistry* / Q000378:metabolism; D000099201:Thymosin beta(4)
D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins; D003598:Cytoskeletal Proteins; D018260:Gelsolin; D011993:Recombinant Fusion Proteins; D013947:Thymosin; D000099201:Thymosin beta(4); C495926:ACTR2 protein, human; C495928:ACTR3 protein, human