The coiled-coil domain is required for HS1 to bind to F-actin and activate Arp2/3 complex.
HS1 (hematopoietic lineage cell-specific protein 1), a substrate of protein tyrosine kinases in lymphocytes, binds to F-actin, and promotes Arp2/3 complex-mediated actin polymerization. However, the mechanism for the interaction between HS1 and F-actin has not yet been fully characterized. HS1 contains 3.5 tandem repeats, a coiled-coil region, and an SH3 domain at the C terminus. Unlike cortactin, which is closely related to HS1 and requires absolutely the repeat domain for F-actin binding, an HS1 mutant with deletion of the repeat domain maintains a significant F-actin binding activity. On the other hand, deletion of the coiled-coil region abolished the ability of HS1 to bind to actin filaments and to activate the Arp2/3 complex for actin nucleation and actin branching. Furthermore, a peptide containing the coiled-coil sequence only was sufficient for F-actin binding. Within cells overexpressing green fluorescent protein-tagged HS1 proteins, wild type HS1 co-localizes with cortical F-actin at the cell leading edge, whereas mutants with deletion of either the coiled-coil region or the repeat domain diffuse in the cytoplasm. Immunoprecipitation analysis reveals that the coiled-coil deletion mutant binds poorly to F-actin, whereas the mutant without the repeat domain fails to bind to both Arp2/3 complex and F-actin. These data suggest that the HS1 coiled-coil region acts synergistically with the repeat domain in the modulation of the Arp2/3 complex-mediated actin polymerization.
Hao
Jian-Jiang
JJ
Department of Pathology, Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, 20855, USA.
Zhu
Jianwei
J
Zhou
Kang
K
Smith
Nicole
N
Zhan
Xi
X
D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing; D020816:Amino Acid Motifs; D000818:Animals; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism; D006801:Humans; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; C104759:HAX1 protein, human; D011506:Proteins