Key result
Human SPIN90 forms a dimer that activates two Arp2/3 complexes to nucleate bidirectional actin filaments, revealing a conserved mechanism for generating anti-parallel actin networks in metazoans.
Why the study?
To understand the basis for how human SPIN90 dimers nucleate bidirectional actin filaments through the Arp2/3 complex.
Answers are grounded in this paper and cite their sources.
The study reveals the structural basis for bidirectional actin filament nucleation by SPIN90 dimers and Arp2/3 complexes, suggesting a conserved mechanism in metazoans.
Branched actin networks nucleated by the Arp2/3 complex play 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. Unexpectedly, 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 dimerises via a 3-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 dimerisation domain in SPIN90 orthologues is conserved in metazoans, suggesting that this mode of bidirectional nucleation is a common strategy to generate anti-parallel actin filaments.
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Liu et al. (2025) studied this question. SPIN90 was evaluated on Structural determination of SPIN90-Arp2/3 complex and actin filament nucleation. Human SPIN90 forms a dimer that activates two Arp2/3 complexes to nucleate bidirectional actin filaments, revealing a conserved mechanism for generating anti-parallel actin networks in metazoans.
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