Details

Autor(en) / Beteiligte

• Balzer, Connor J.
• Wagner, Andrew R.
• Helgeson, Luke A.
• Nolen, Brad J.

Titel

Dip1 Co-opts Features of Branching Nucleation to Create Linear Actin Filaments that Activate WASP-Bound Arp2/3 Complex

Ist Teil von

• Current biology, 2018-12, Vol.28 (23), p.3886-3891.e4

Ort / Verlag

England: Elsevier Ltd

Erscheinungsjahr

2018

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• When activated by Wiskott-Aldrich syndrome proteins (WASP), Arp2/3 complex nucleates branched actin filaments important for processes like cellular motility and endocytosis [1]. WASP-mediated activation of Arp2/3 complex requires a preformed actin filament, ensuring that activation by WASP creates branched instead of linear filaments. However, this biochemical requirement also means that assembly of branched actin networks must be primed with an initial seed filament [2–4]. We recently described a class of activators called WISH/DIP/SPIN90 (WDS) proteins, which, unlike WASP, activate Arp2/3 complex without a preformed filament [4]. Although this property may allow WDS proteins to serve as seed filament generators, it is unknown whether actin filaments nucleated by WDS-activated Arp2/3 complex can activate WASP-bound Arp2/3 complex. Further, despite their potential importance as branched actin network initiators, little is known about how WDS proteins turn on Arp2/3 complex. Here, we use two-color single-molecule total internal reflection fluorescence (TIRF) microscopy to show that Dip1, the S. pombe WDS protein [5], co-opts features of branching nucleation to activate Arp2/3 complex. Specifically, it activates Arp2/3 complex to nucleate linear filaments analogous to the branch created by WASP-mediated activation. The barbed ends of Dip1-Arp2/3 nucleated filaments are free to elongate, and their pointed ends remain anchored to Dip1-bound Arp2/3 complex. The linear filaments nucleated by Dip1-bound Arp2/3 complex activate WASP-bound Arp2/3 complex as potently as spontaneously nucleated or branched actin filaments. These observations provide important insights into the regulation of Arp2/3 complex by its activators and the molecular basis for initiation of branched actin networks. •Dip1 co-opts aspects of branching nucleation to activate Arp2/3 complex•Dip1 binds the pointed ends of actin filaments indirectly through Arp2/3 complex•Actin filaments nucleated by Dip1-Arp2/3 complex activate WASP-bound Arp2/3 complex Balzer et al. use multi-color single-molecule TIRF microscopy to show actin filaments nucleated by Dip1-bound Arp2/3 complex stimulate branching nucleation by another Arp2/3 complex activator, WASP. Their data support a model in which Dip1 provides the first actin filaments to kickstart assembly of branched actin networks.