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<p>Branched actin networks nucleated by the Arp2/3 complex have critical roles in various cellular processes, from cell migration to intracellular transport. However, when activated by WISH/DIP/SPIN90-family proteins, Arp2/3 nucleates linear actin filaments. Here we found that human SPIN90 is a dimer that can nucleate bidirectional actin filaments. To understand the basis for this, we determined a 3-Å-resolution structure of human SPIN90–Arp2/3 complex nucleating actin filaments. Our structure shows that SPIN90 dimerizes through a three-helix bundle and interacts with two Arp2/3 complexes. Each SPIN90 molecule binds both Arp2/3 complexes to promote their activation. Our analysis demonstrates that single-filament nucleation by Arp2/3 is mechanistically more like branch formation than previously appreciated. The dimerization domain in SPIN90 orthologs is conserved in metazoans, suggesting that this mode of bidirectional nucleation is a common strategy to generate antiparallel actin filaments.</p>

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Arp2/3-mediated bidirectional actin assembly by SPIN90 dimers

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年9月15日

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  • Tianyang Liu,
  • Luyan Cao,
  • Miroslav Mladenov,
  • Guillaume Romet-Lemonne,
  • Michael Way,
  • Carolyn A. Moores

摘要

Branched actin networks nucleated by the Arp2/3 complex have critical roles in various cellular processes, from cell migration to intracellular transport. However, when activated by WISH/DIP/SPIN90-family proteins, Arp2/3 nucleates linear actin filaments. Here we found that human SPIN90 is a dimer that can nucleate bidirectional actin filaments. To understand the basis for this, we determined a 3-Å-resolution structure of human SPIN90–Arp2/3 complex nucleating actin filaments. Our structure shows that SPIN90 dimerizes through a three-helix bundle and interacts with two Arp2/3 complexes. Each SPIN90 molecule binds both Arp2/3 complexes to promote their activation. Our analysis demonstrates that single-filament nucleation by Arp2/3 is mechanistically more like branch formation than previously appreciated. The dimerization domain in SPIN90 orthologs is conserved in metazoans, suggesting that this mode of bidirectional nucleation is a common strategy to generate antiparallel actin filaments.